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Radiotracer study of some aspects of the role of mosses in the biogeochemical cycle Otchere-Boateng, Jacob 1972

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tV A RADIOTRACER STUDY OF SOME ASPECTS OF THE ROLE OF MOSSES IN THE BIOGEOCHEMICAL CYCLE by JACOB OTCHERE-BOATENG . / B.S.F., University of British Columbia, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of FORESTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1972 In presenting this thesis in partial fulfilment of the require-ments for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Depart-ment or by his representative. It is understood that copying or publi-cation of this thesis for financial gain shall not be allowed without my written permission. J. Otchere-Boateng Department of Forestry University of British Columbia Vancouver 8, Canada October 6, 1972. ABSTRACT Some aspects of the role of mosses in the biogeochemical cycle of a coastal forest ecosystem in British Columbia were studied using 137 radioisotopes. The average concentration of Cs from atmospheric 2 fallout in ground-dwelling mosses was 36.7 pCi/g or 6025 pCi/m . Concen-trations increased with precipitation, with the highest concentrations being found in Plagiothecium undulatum (Hedw.) B.S.G. and Sphagnum squar-85 134 rosum Crome. Experiments involving a dual labelling with Sr and Cs indicated that nutrients which are leached from stem tissues of host plants, and those in the crown washings of the overs torey trees are sources of nutrients for epiphytic mosses. Epiphytic mosses were e f f i -cient in f i l t e r i n g radioisotopes from solution, the activity of through-f a l l and stemflow being reduced after passage through epiphytic mosses 85 134 by up to 70%. Sr and Cs concentrations in ground-dwelling mosses under western hemlock trees (Tsuga heterophylla (Rafn.) Sarg.) followed the distribution pattern of throughfall nutrients which decreased from close to the stem towards the crown edge. i i TABLE OF CONTENTS Page ABSTRACT . . . . . . . . . . . i i TABLE OF CONTENTS i i i LIST OF TABLES . . . . . . . . . vi LIST OF FIGURES . . . . . . . . v i i ACKNOWLEDGMENT . . ix CHAPTER 1. INTRODUCTION 1 CHAPTER 2. LITERATURE REVIEW . . . . . . . . . 3 2.1. Concept of ecosystem and biogeochemical cycle . 3 2.2. Importance of mosses in the forest ecosystem . . 4 2.2.1. Productivity of mosses 4 2.2.2. Mosses and tree nutrition 6 2.3. Epiphytic adaptation 6 2.3.1. Factors controlling (moss) epiphytism. . 8 2.3.2. Sources of nutrients for epiphytic mosses 10 2.4. Leaching phenomenon 11 2.4.1. Patterns of distribution and the dynamics of tree leachates on the forest floor. . 12 2.5. Mosses as concentrators of toxic substances. . . 15 2.6. Fission product isotopes: their mode of contaminating vegetation 16 1 ?4 85 2.7. Biological cycle of 1 -Cs. and ° 3Sr 17 i i i i v Page CHAPTER 3. THE RESEARCH AREA AND THE EXPERIMENTAL PLOTS 23 3.1. The research area 23 3.2. Description of the experimental plots 23 CHAPTER 4. METHODS 31 4.1. Radiotracer technique 31 4.2. Inoculation of trees on the experimental plots . 32 4.2.1. The inoculation procedure 33 4.3. Experimental design and sampling 34 4.3.1. Study of natural radioactivity of mosses 34 4.3.2. Some nutrient sources for epiphytic mosses 34 Leachate from stem tissues as a source of nutrients . . . . 34 Throughfall as a source of nutrients . 36 4.3.3. Patterns of distribution of throughfall leachates on the forest floor 38 4.3.4. Concentration of radionuclides by various ground mosses 38 4.3.5. Penetration of radioisotopes into the soil . . . . 41 4.3.6. Sampling of the inoculated trees . . . . 41 4.4. Laboratory work 41 4.4.1. The sc i n t i l l a t i o n counter 43 CHAPTER 5. RESULTS AND DISCUSSION 44 137 5.1. Cs fallout activity levels of mosses . . . . 44 5.2. Primary nutrient sources for epiphytic mosses. . 52 5.2.1. Epiphytic mosses as f i l t e r s of crown-washed nutrients 52 V Page 5.2.2. Leachates from the stem as a source of nutrients for epiphytes . 54 Leaching of 8 5 S r and 1 3 4 C s from vine maple stems . . . . 54 Contamination of epiphytic mosses by stem leachates (85 S r and 134 C s) 61 5.3. Nutrients and epiphytic adaptation 61 5.4. Interspecific translocation of mineral elements 63 5.5. Nutrients in throughfall and forest floor nutrient dynamics 64 5.5.1. 8 5 S r and 1 3 4 C s activity levels in the inoculated hemlock tree needles and twigs 64 5.5.2. The removal of 1 3 4 C s and 8 5 S r from the tree crowns in throughfall precipitation 67 85 5.5.3. The pattern of throughfall input of Sr and '3^Cs to the forest floor 69 5.5.4. Nutrient distribution on the forest floor , 73 1 OA OC 5.5.5. Differential leaching of Cs and Sr in the forest floor 74 CHAPTER 6. CONCLUSIONS . . 75 REFERENCES . . 77 APPENDIX . . . . . . . . . 92 LIST OF TABLES Table Page 1 Biomass of bryophytes in nine ecosystems 5 2 Ecosystematic units and t h e i r d i s t r i b u t i o n in the research s i t e 27 1 ^7 3 Cs f a l l o u t a c t i v i t y of mosses i n the UBC Research Forest and Endownment Lands 45 4 Comparison of f a l l o u t a c t i v i t y levels of three mosses 47 5 Comparison of amounts of f a l l o u t a c t i v i t y in 5 locations 48 137 6 Values of Cs natural f a l l o u t a c t i v i t y in mosses from other sources 51 7 Efficiency of epiphytic mosses in f i l t e r i n g radio-nuclides in throughfall and stemflow waters 53 8 8 5 S r and 1 3 4 C s in stemflow waters of inoculated vine maple trees . . 55 oc 1OA 9 Sr and Cs concentration in tissues of labelled maple trees 59 OC 1 OA A 10 Sr and Cs concentrations (uCi/10 per gm) in epiphytic mosses and a vine maple tree at various distances (cm) from the point of inoculation . . . . . 60 11 Radioactivity (pCi/g) of epiphytic mosses on inoculated vine maple trees . . 62 12 Volumes and chemical properties of throughfall water (under a single western hemlock tree) with respect to distance from the tree stem . . . . . . . . . . . . . 70 13 D i f f e r e n t i a l leaching of Sr and , J X s in the forest f l o o r 74 vi LIST OF FIGURES Fi gure Page 1 Monthly mean temperatures during the experimental period (July 1971-July 1972) . 24 2 Monthly precipitation during the experimental period (July 1971-July 1972) 24 3 Location of the radioisotope experimental plots . . . . 25 137 4 Sampling sites for Cs fallout study . . . 35 5 Plot #4 showing the inoculated vine maple trees and the stemflow collecting systems 37 6 Layout of the 15 throughfall collectors on Plot #3 . . . 39 7 Plot #3 showing the inoculated hemlock trees and some of the throughfall collectors 40 8 A close view of a throughfall (or stemflow) collector . 40 85 9 Changes in activity of Sr in twigs and needles of inoculated hemlock trees 66 134 10 Changes in activity of Cs in twigs and needles of inoculated hemlock trees 66 85 11 Distribution patterns of Sr in throughfall under inoculated hemlock tree canopy 68 134 12 Distribution patterns of Cs in throughfall under inoculated hemlock tree canopy . 68 13 Patterns of throughfall water distribution under hemlock tree canopy . . . . . . . . 68 14 Patterns of K and Ca distribution under hemlock tree canopy . . 71 15 Volume of throughfall under hemlock tree canopy . . . . 71 vi i Changes of pH in throughfall water of hemlock tree canopy 85 134 Changes in the activities of Sr and Cs in twigs and needles of individual inoculated hemlock trees . . . . ACKNOWLEDGMENT I wish to acknowledge my gratitude to Dr. J. P. Kimmins of UBC Faculty of Forestry for his valuable suggestions and guidance during the course of this study. Thanks are expressed also to the other members of my committee, Dr. J. Worrall, Faculty of Forestry, Dr. T. M. Ballard, Department of Soil Science and Faculty of Forestry, and Dr. W. B. Scho-f i e l d , Department of Botany for their advice and constructive criticisms. I am grateful to my fellow students, M. Feller and M. Fraker, and Mr. D. Moon (laboratory assistant), for their help in both the f i e l d and laboratory work; to the Director and staff of the UBC research forest for their services; to Dr. A. Kozak and his assistants for help with the s t a t i s t i c a l analyses; to the staff of McMillan Forestry/Agriculture Library; to Miss Piovesan who typed the final copy of the thesis and to many friends who in diverse ways made my stay here possible. The study was financially supported by the Canadian Inter-national Development Agency and the UBC Faculty of Forestry. ix CHAPTER 1 INTRODUCTION The biological cycling of chemical elements is one of the main functional processes controlling ecosystem productivity. Its study fur-nishes us with information on the precise amount of elements involved in the l i f e cycle of plants and animals and their subsequent fate until return to the soil or water. This is important for practical recommen-dations in forestry and in agriculture; for example, in f e r t i l i z a t i o n programmes. Because of the importance of biological cycling of chemical elements, i t has been widely studied in many forest ecosystems, and reviews and summaries of results have been published (eg. Rodin and Bazilevic 1967, Ovington 1968) for many forest types. Some aspects of the cycle in tropical areas have been studied by Richards (1952), Bartho-lomew et al_. (1953), Greenland and Kowal (I960), Eyre (1963), Klinge and Ohle (1964), MacArthur and Connell (1966) and Odum (1970). Duvigneaud and Denaeyer-de-Smet (1967, 1970) and Ovington (1962, 1965) have summarized the dynamics of mineral cycling in the temperate deciduous forests. Various aspects of mineral cycling within Douglas-fir (Pseudotsuga men- zies i i Franco) ecosystems in Washington have been studied by Gessel et al_. (1961), Heilman and Gessel (1963), Cole and Gessel (1965), Gessel and Cole (1965), Riekerk and Gessel (1965), Cole et al_. (1967) and Riekerk (1967, 1971). 1 2 None of these studies dealt exp l i c i t l y with the role of mosses in cycling in spite of the importance of mosses in many forest regions. This is a particularly serious omission in areas such as the Pacific northwest where mosses occur extensively as carpets on the forest floor, on decaying wood, or as epiphytes. This lack of information led to the present study on the role of mosses in some aspects of the biogeochemical cycle in the west coast forest ecosystems of British Columbia. The study is in three parts. F i r s t l y , the ability of different species of mosses to concentrate environmental pollutants, and therefore their potential as indicators of environmental pollution is examined. Secondly, the possible primary nutrient sources of epiphytic mosses is investigated. The purpose here is to test, qualitatively, the hypothesis that plant bark tissues contribute nutrients to stem-flow water and at the same time demonstrate that epiphytic mosses obtain some nutrients from their hosts through leachates from the stem tissues. It also attempts to assess the contribution of throughfall leachates to the nutrition of epi-phytic mosses. Thirdly, a study of patterns of distribution of leachates o c i on (radionuclides Sr, Cs) in throughfall, the interception of leachates by ground-dwelling mosses, and the movement of these leachates in the forest floor (with ground cover and without ground cover) is reported. i CHAPTER 2 LITERATURE REVIEW 2.1 Concept of ecosystem and biogeochemical cycle The term "ecosystem," meaning the total assemblage of organisms and their environment was introduced by Tansley in 1935. Ecosystem is largely synonymous with "biogeocoenose" conceived by the Russian scien-t i s t , Sukachev in 1944 (Hills 1960). The importance of the ecosystem concept in relation to forest research has been stated by Ovington (1962) as follows: Whilst the ecosystem concept has value in relation to a number of forestry problems, its greatest contribution to improving forestry practice probably will be. that i t provides a sound foundation for investigations designed to elucidate the func-tional processes of woodlands and to show the bearing of these processes on forest productivity on a long-term basis. Linde-man (1942) believed the concept of ecosystem to be of funda-mental importance in interpreting the data of dynamic ecology. If forest research is to be fully effective, i t needs to be orientated towards obtaining a better appreciation of eco-system dynamics; particularly in relation to quantitative studies of the biological and physical processes affecting productivity and the accumulation, transformation and flow of energy and materials (water, mineral elements, etc.) through different woodland ecosystems. Under this concept a l l the components of the ecosystem (soils, living organisms and environmental factors) are integrated and each has a role to play. Even the smallest component present may be very important in the functioning of the system. It may have a high turnover rate, 3 4 form part of a c r i t i c a l pathway, or play a role in spatial or temporal distribution in the system. Hence, to arrive at a complete understanding of the functioning of ecosystems a l l components must be investigated. The investigations may involve three main aspects; namely, energy, water and nutrient dynamics (Ovington 1968). The biogeochemical cycle (involving nutrient and other elemental dynamics) is a more or less cyclic movement of chemical elements in the biosphere. Two major routes are recognized; namely, the biological cycle and geo-chemical cycle. The former involves the uptake or absorption of elements from the s o i l , the retention of the elements in the biomass and the return of elements to the soil via stemflow, leafwash, l i t t e r f a l l or death of organisms. The latter involves the input and output of chemical elements to and from the ecosystem. The inputs include: pre-cipitation, minerals from blown dust, weathering of parent rock. The outputs include losses through drainage (surface runoff or downward move-ment in groundwater). 2.2 Importance of mosses in the forest ecosystem 2.2.1. Productivity of Mosses. Bryophytes contribute greatly to the plant biomass in many tundra, coniferous* temperate rainforest, and tropical rainforest ecosystems. Forman (1969) gives the bryophyte biomass for nine different ecosystems (Table 1). Wojcik (1970) found the biomass of mosses in a dry pine forest in Poland to be 1580 kg/ha. This value was estimated to be seven times greater than the biomass of the herb layer; 5 TABLE 1 Biomass of bryophytes in nine ecosystems (after Forman 1969) ,s Ecosystems kg/ha Alpine 1695 2384 471 581 612 Krummholz Coni ferous 2 3 4 5 Coniferous deciduous 6 7 252 84 ecotone Northern hardwoods Oak woods 8 9 31 22 The annual biomass increase of the mosses in this forest was estimated to be one third of the total biomass (527 kg/ha), and three times the annual production of the herb layer. Weetman and Timmer (1967) found in a black spruce forest of the Boreal forest region in eastern Canada that the annual productivity of mosses was one third to one half that of the spruce canopy and boles. According to their data the amount of nutrients in the moss layer represented 9 percent to 40 percent of the total nutrients contained in the above-ground part of the trees. Annual uptake of nitrogen, phosphorus, potassium and magnesium by moss was estimated to be 23% to 53% of the uptake of these elements by trees. Rodin and Bazilevich (1967) have stated that l i t t e r accumulation in forests with a well developed moss layer is greater than forests with poorly developed moss cover. 6 2.2.2. Mosses and tree nutrition. Mosses growing in a forest are thought to receive their chemical elements from dust or from substances leached from the overstorey canopy by rain (Tamm 1953, 1964; Weetman and Timmer 1967). Most of these chemical elements are retained until the mosses decompose. According to Weetman and Timmer's (1967) estimate, the dead feather.moss (Calliergon schreberi (Brid.) Grout) segments may take from five to twelve years to decompose to the point where they are not readily distinguishable. During decomposition, nitrogen is mineralised more rapidly than from decomposing spruce needles. Hence, in a forest stand where available nitrogen is deficient in the s o i l , the decomposition of the moss layer may be a primary source of nitrogen to the trees (Weet-man 1967, Weetman and Timmer 1967), and a rapid means of entry of nitrogen contained in rainfall into the nitrogen cycle of the stand (Weetman and Timmer 1967). The raw humus formed by mosses favours optimum mycorrhizal development in pines (Melin 1930) and spruce (Melin T930, Weetman and Timmer 1967), probably as the result of the availability of this source of nitrogen. 2.3. Epiphytic adaptation The term "epiphytic" (derived from the Greek words epi, "upon" and phyton, "plant") refers to a plant which grows upon another plant merely for support and which obtains no sustenance from its host. This definition is sometimes extended to cover plants which are fastened on non-living objects like rocks, buildings or telegraph wire (Silverberg 7 1967). However, for the purpose of this thesis the use of the term epiphyte will be limited to those plants which grow above ground level on trees (trunks, branches or leaves). Those epiphytes which in later stage of development grow nearer the ground and extend air roots to the soil ( i . e . , the hemiepiphytes of Ford-Robertson 1971) are not considered in this study as true epiphytes. The epiphytic adaptation is found among several great divisions of the plant kingdom and forms an important vegetative category of the forest ecosystem. In the temperate regions such as British Columbia only the lower plants such as the algae, lichens, liverworts, mosses and some ferns have developed this adaptation. It is estimated (Schofield, personal comm. 1972) that about 68 species of mosses and 35 liverwort species frequently grow as epiphytes in the province. An additional 40 species of mosses and 23 species of li v e r -worts are occasionally seen as epiphytes. The following l i s t shows the genera of mosses and liverworts whose members are most frequently found as epiphytes in the province. Mosses Alsia Mohr Antitrichia Brid Claopodium (Lesq. & James) Neckera Hedw. Orthotrichum Hedw. Pterigynandrum Hedw. Pylais i e l l a Kindb Scleropodium B.S.G. biota Mohr Zygodon Hook & Taylor Ren. & Card. Dendroalsia B r i t t Homalia (Brid). B.S.G. Homalothecium B.S.G. Isotheciurn Hedw. Liverworts Cololejeunea (Spruce) Schiffn Metzgeria Raddi Porella L. Douinia Buch Frullania  Lophocolea Dumort Ptilidium Nees Radula Dumort Scapania Dumort 8 Epiphytic adaptation in the tropics includes many flowering plants in addition to those types of plants found growing epiphytically in the temperate region. Craighead (1963) noted that bromeliads (called "airplants" or in some species "wild pines"), orchids (also called "air-plants") , Pej?pjyiQmm sppj.3,, f v g s a n d mi.sjtTetoe'cac^us--a re-epiphytic on trees in the Everglades National Park in Florida. For the family Orchidaceae (Orchids).alone, Sanford (1969) found that of the total of 400 species identified in West Africa, 239 species in 34 genera are always or often epiphytic on shrubs or trees. 2.3.1. Factors controlling (moss) epiphytism. The question is raised whether or not epiphytes associate^themselves specifically with some particular "host" species. Evidence from R'oltturn" (1964) in Malaya and Sanford (1969) in Nigeria indicates that epiphytic orchids do not grow on specific plant hosts, but rather, they are found associated with some characteristic features of the "host." These features include rough1 bark, large horizontal branches, and exposure, which is controlled by leaf f a l l and leaf shading (Sanford 1969). The importance of these characteristics, according to Sanford, is pronounced when some factors in the environment are limiting. Thus, on favourable sites both smooth and rough barks may carry epiphytes while in less favourable conditions only rough barked hosts w i l l . Hosokawa and associates (Hosokawa et al_. 1964) have suggested that the distribution of corticolous mosses and lichens on their hosts is controlled by microclimatic factors such as light intensity, atmospheric 9 relative humidity and evaporation. They stated that the degree of shade tolerance of the epiphytic plant species is responsible for the lower limit while the degree of drought tolerance determines the upper limit of distribution on trees. Brodo (1961) showed that the chemical composition of the bark may influence the distribution of epiphytic plants. It was demonstrated that the bark exudates of Quercus species could be injurious to some 1ichens. Grubb ejt al_. (1968) included competition as an important factor in determining habitat preference of epiphytes. Grubb and co-workers found that with more favourable water relations, but less intensive shade, an hierarchy of competition takes place. For example, on an extending branch, Ulota crispa (Hedw.) Brid. (and other early invaders) could be suppressed by a later invader such as Hypnum cupressiforme Hedw. which in turn is suppressed by Dicranum scoparium Hedw. As with other plant species, nutrient availability is also a very important factor controlling the distribution of epiphytic plants. Carlisle et al_. (1967) stated that in addition to microclimate, bark texture, and bark composition, the chemical composition of stemflow waters could contribute greatly to the natural selection of epiphytic lichens and bryophytes. Selection may be influenced by it s nutrient composition, pH, and transport of harmful substances to and from the epiphytes. 10 2.3.2. Sources of nutrients ,for epiphytic mosses. Attempts have been made to find the possible source of nutrients for epiphytes. Tamm (1953) has studied the growth and nutrition of Hylocomium splendens in Sweden. He attributed the sources of mineral supply for the ground dwelling mosses as well as the epiphytic mosses to leachates from the tree crowns, including f o l i a r leachate, leachate of animal excrement, l i t t e r , salt spray, and atmospheric dust. According to Tamm (1953), the importance of dust in the nutrition of epiphytic plants has long been recognized (Dixon 1881, Sernander 1912, Rietz 1932* and Waldheim 1944). The data related to this question have been published by Persin (1925) and Wherry and Cooper (1928). The atmospheric dust may be washed down With rain, deposited on the mosses directly, or be deposited on the tree crown and later washed down by rain. It was. suggested by Tamm (1953, 1964) that mosses obtain their nitrogen by direct fixation from the atmosphere. This nitrogen source may be supplemented by ammonia and nitrate in rain and perhaps the nitro-genous substances coming down from the trees. Grubb et al^ (1968) stated that the nitrogen supply may come from nitrogenous compounds produced by nitrogen-fixing bacteria on leaves and bark of trees. Grubb et a]_. (1968) have discussed the type of soil which forms under large epiphytic species of mosses on large branches and trunks. This soil is developed mainly from bark fragments, animal detritus, dust and remains of various mosses and lichens. This, they said, may provide nutrients to the epiphytic mosses. After analysing the bark tissue of 80-year old oak trees, Carlisle et a l . (1967) suggested that the bark tissues contribute nutrients to the stemflow water which in turn provide nutrients to the epiphytic mosses. This is true with calcium which comes down in these waters in appreciable quantities. 2.4. Leaching phenomenon The phenomenon of leaching (defined by Tukey (1970a) as loss of inorganic and organic metabolites from above-ground plant parts by the action of aqueous solutions, including rain, mist, and dew), was recognized in about 1804 by Saussure (Tukey e_t al_. 1958, Mina 1965) and experimentally demonstrated independently in 1883 by Buchenan and von Homeyer (Tukey ejt al_. 1958). Detailed study of the phenomenon in forest trees was not undertaken until about two decades ago, however, when Tamm showed that the precipitation collected beneath the canopies of six deciduous species and two conifers in Sweden contained greater amounts of chemical elements than the precipitation of the open area for the same sampling periods (Tamm 1951, 1953). This fact has been confirmed by some workers in other parts of the world (Mes 1954, Will 1955, 1959, Stenlid, 1958, Madgwick and Ovington 1959, Sviridova 1960, Nye 1961, Greenland and Nye 1964, Carlisle 1965, Egunjobi 1971). Much of this work f a i l s to quantify the phenomenon precisely, however, since aerosols and extraneous substances deposited on the vegetation contribute to the increase of nutrients i n the precipitation collected under the forest canopy. Thus, observed differences in the chemistry of incident and net precipitation are not necessarily due to 12 leaching of nutrients from the plant tissues. Tukey and co-workers cl a r i f i e d this by demonstrating conclusively using radio-isotopes that the above-ground plant parts are susceptible to leaching of their mineral nutrients, carbohydrates, amino-acids, organic acids, and growth-regulating substances (Long ejt al_. 1958, Tukey e_t al_. 1958, Tukey and Tukey 1962, Tukey and Morgan 1962, Tukey et al_. 1965, Meckleburg et al_. 1966, Tukey 1970a, 1970b). The factors controlling leaching from leaves include: the intensity, velocity, and periodicity of rain (Tukey and Tukey 1959, Voigt 1960a); the age of the leaves, with susceptibility to leaching increasing with age (Tukey ejt al_. 1958, Tukey and Tukey 1959); type and nature of plant; rate of replenishment of leached materials, and the relative Teachability of the substance concerned (Tukey et al_. 1958). The importance of leaching in crop management, especially in high rain f a l l areas, has been stated by Tukey (1970a). It has influence on yie l d , quality, and nutritive value of crops, the susceptibility of plants to diseases, the propagation and nutrition of plants and plant ecosystem development. It should also be mentioned specifically that these leachates have some influence on soil properties (Franklin et a l . 1967) and nutrition of epiphytes and some understorey vegetation. Tamm (1953) demonstrated that Hylocomium splendens (Hedw.) B.S.G. obtains its nutrients from leachates from overstorey crowns. 2.4.1. Patterns of distribution and the dynamics of tree  leachates on forest floor. The cycling of leachates coming down in rain 13 from the aerial parts of plants to the ground is an important aspect of biogeochemical cycle studies. Leachates may get to the floor either in throughfall or in stemflow. Throughfall as defined by Helvey and Patric (1965) is that portion of the gross rainfall which reaches the forest floor through spaces in the vegetative canopy as drip from leaves, twigs and stems. That portion of the gross rainfall which is caught on the canopy and reaches the l i t t e r or mineral soil by running down the stems is termed stemflow (Helvey and Patric 1965). Voigt (1960a) and Mina (1965) have demonstrated that stemflow water contains greater concentration of chemical constituents than throughfall. Voigt (1960a) found an average concentration of twice as much nitrogen and phosphorus and more than three times as much potassium and calcium in stemflow than in canopy drips, while Mina (1965) observed an average of five times as much N, K, and Mg and about twelvesttmes as much Ca in stemflow as in throughfall. According to Mina (1965), the contribution of precipitation in stemflow is associated with the total amount of precipitation, the bark charac-t e r i s t i c s , the architecture of the crown and its leaf formation, as well as the density of the stand and the wind regime during the precipitation peri od. Franklin e_t al_. (1967) and Gersper (1970) have shown that fallout radioisotopes in a forest soil are distributed in radially sym-metrical patterns with respect to the tree trunks. The quantities of radionuclides varied with distance from the stems (usually decreasing). Tamm (1953) also reported a steady increase in amounts of different substances in rainwater from the opening towards the centre of the tree 14 crown. A similar systematic distribution pattern for rainfall was found by Voigt (1960b). According to Voigt (1960b) a large portion of the precipitation impacting the canopies of red pine (Pinus resinosa A/it), eastern hemlock (Tsuga canadensis (L) Carr.) and American beech (Fagus  grandifolia Ehrh) was distributed to the soil in a relatively narrow band around the base of the trees. Zinke (1962) has reported that soil properties under single forest trees generally exhibit radial symmetry with respect to the tree. He attributed this symmetric pattern of soil properties to the effects of bark l i t t e r , leaf l i t t e r , and to adjacent openings or neighbouring trees. It is well documented that understorey vegetation, especially mosses and litter,} are able to intercept part of the elemental content of rain. Thus the movement of these elements into the mineral soil layer is delayed until decomposition and mineralization of this vege-137 tation or l i t t e r occur. Rickard (1967) showed that Cs present in the forest was concentrated either in the moss carpet or in the l i t t e r . 137 However, the highest concentrations cof Cs were associated with mosses rather than l i t t e r ((:Ri:cka\rdi 1!97T.)-. When mosses were lacking, l i t t e r had a higher radionuclide content than either the mineral soil or under-storey shrubs such as snowberry (Symphoricarpos albus (L.) Blake), mountain huckleberry (Vaccinium membranaceum Torr.), and salal (Gautheria shall on Pursh). Rickard (1967) also explained that the abi l i t y of mosses to concentrate more radionuclides than l i t t e r , soil or foliage is probably due to the intricately branched nature of the moss carpet that contributes large surface area per gram of dry weight. Litter refers to the decomposing vegetative materials of the forest floor. 2.5. Mosses as concentrators of toxic substances 15 It has been shown that mosses and lichens (especially the epiphytic types) are able to absorb and tenaciously retain greater levels of elemental substances such as lead (Ruhling and Tyler 1965) and radio-active fallout substances from the atmosphere than are other plants. Shacklette (1965) found that large amounts of elements which are generally toxic to plants did not,produce toxicity symptoms in the bryophytes that contained these elements. The efficiency of mosses as concentrators of radioactive airborne debris has been demonstrated by Gorham (1959), Svensson and Liden (1965a, 1965b), Svensson (1966), Rickard (1966, 1967, 1971), Osburn (1967), Bovard and Grauby (1966) and Odum (1970). Bovard and Grauby's studies indicated that mosses absorb radionuclides directly from the atmosphere. This is supported by the finding that bryophytes concentrate the rare earth elements in their tissues even when growing on substrates in which these elements are not detected (Shacklette 1965). The adsorbed elements show l i t t l e ( i f any) leaching from the plants (Svensson 1966, Osburn 1967). Osburn (1967) also found a reliable estimate of regional fallout by means of Sphagnum moss cores, and Shacklette (1965) stated that: bryophytes may be useful in regional geochemical evaluation because of their pronounced abi l i t y to concentrate the rare elements that may not be detected in other sampling media. This sensitivity to, and a b i l i t y to concentrate elemental substances from the atmosphere is very important in a world characterized by in-dustrialization, rapid development of atomic energy for military and peaceful purposes, and the spread of potentially dangerous material into the environment. 16 2.6. Fission product isotopes: their mode of contaminating vegetation 90 137 Of about 200 fission product isotopes, only Sr and Cs play an important long term role in contaminating man's food and body (Miettinen 1967); they become a part of mineral nutrition in plants and animals. Miettinen (1967) explained that their harmful effect is due to their high yield in fission products (5-6 atom percent), their long physical 90 137 half-lives ( Sr = 28 years, Cs = 29 years) and their effective absorp-tion by living organisms because of their chemically close similarity to important bioelements (Sr to Ca, Cs to K). High levels of activities of these two radioactive elements have been recognized in vegetation in the arctic regions of Finland and Alaska (Salo and Miettinen 1964, Watson et a]_. 1964), and their transfer into herbivores and human beings has been established (Russel 1966, Hanson 1966, Aberg and Hungate 1966). The two radionuclides are mainly produced (as the result of atmospheric bomb tests) in a monoatomic state in the stratosphere (the almost weatherless part of the atmosphere). They are transferred from the atmosphere to the earth's surface either by rain or by gravitational settling. Those radioactive particles having a diameter of more than 1 urn come down to the surface mainly by collision with f a l l i n g raindrops (Green-f i e l d 1957). Greenfield, (ilt957.);sahdivan dercoWesthuijze'h (1-969)• have dis-cussed ra 1 mode iii sfiop a -.relationship .between" tfaili],out .'deposition; air-concen-triatirQnland r a i n f a l l . 90 According to Pavlotskaya e_t al_. (1966), Sr comes to the 137 surface of the earth mainly in water-soluble compounds while Cs is 17 received in almost water-insoluble forms (68-93%). Contamination of vegetation by these radionuclides may be direct or indirect (Russel 1966a, 1966b; Comar and Langemann 1966, Aakrog 1969). Direct conta-mination occurs when the aerial parts of the vegetation (eg. the foliage) absorb the radionuclide through rain, gravitational settling, or gaseous or Brownian diffusion to the surface (Chadwick and Chamberlain 1970). Adsorption is often followed by absorption into the tissues. This mode of contamination is described as "rate dependant" since the amount deposited varies with the'rate at which fallout settles. The fallout deposited on the aerial, parts of plants may be lost through radioactive decay, activity removal in particulate form from plant surfaces (eg. by atmospheric precipitation, wind, and gravitational forces), translocation to the roots, volatilization (eg. radio-iodine in hot climates), l i t t e r f a l l (eg. leaves, needles, branches) and dying back or weathering of leaves or their surface layers (cf. Chamberlain 1970, Aleksakhin ejt al_. 1970). Indirect contamination of vegetation involves direct deposition of the radioactive aerosols into the soil where they are absorbed by plants through their root system. This type of contamination is controlled by the total amount of radionuclides present in s o i l : hence i t is regarded as "cumulative dependent." The detailed c r i t i c a l pathways of fission products in terms of human health have been treated by Comar and Langemann (1966) and Russel (1966b). 2.7. Biological cycle of 1 3 4 C s and 8 5 S r 134 Cs, an alkali metal element, is commonly used as a tracer in biological investigations because of i t s convenient h a l f - l i f e (2.07 18 12g years), availability (manufactured readily from stable cesium, or Ba) and easily measurable radiation (Davis 1963). Most other alkali metals have half-lives which are either too long or too short for use in f i e l d studies. A knowledge of radio-cesium cycling is of practical importance since i t provides information on the transfer of stable and radioisotopes of cesium and related alkali metal elements in natural environments (Dodd and Van Amburg 1970). It is physically and chemically similar to potassium and behaves somewhat like i t in physiological process (Davis 1963), but according to Moon and Kimmins (unpublished manuscript) there are very few cases that cesium will be a physiological mimic for potassium. The •I o^l OC results of their experiment indicate that Cs and Rb are close mimics 42 of each other but that they are not biologically equivalent to K and therefore do not provide adequate mimics of potassium in biological systems. It was further indicated in the study that results which suggest a simi-lar i t y between Cs or Rb and K may be due to saturation of:the membrane transport mechanism(s) which govern selection. When radiocesium is inoculated into the stem of plants, i t is rapidly transferred to the foliage (Olson 1968), and downwards to the roots (Stenlid 1958, Waller and Olson 1964, Witkamp and Frank 1964, Olson 1965, Waller and Olson 1967) and hence to the mineral soil and associated organic matter (Witherspoon 1964, Waller and Olson 1967). In the s o i l , cesium is strongly absorbed and bound-to i t (Amphlett and MacDonald 1956, Klechkovsky and Tselischeva 1957, Evans 1958, Nishita et al^. 1958). The sorption of cesium is by ion exchange absorption, and part of the cesium absorbed is fixed in non-exchangeable form making 19 i t almost unavailable to plants (Klechkovskii and Gulyakin 1957). De-sorption of cesium is brought about by cations of neutral salts (Gulyakin and Yudintseva 1958). Almost a l l cesium adsorped is bound in the organic matter and the upper few centimetres of the mineral soil (Low and Edverson 1959, Walton 1963, Franklin et a]_. 1967, Ritchie et al_, 1967, Ritchie et al_. 1970, Jordon 1970, Kline et al_. 1970). Absorption of cesium by plants is inhibited by the strong sorptive forces between the cesium ion and soil particles and only a small proportion of the adsorbed cesium is available to plants (Davis 1963). According to Barber (1964), uptake of cesium by plants is controlled by the cation exchange capacity of the soil organic matter. Calcium and magnesium concentrations have been found to influence uptake (Shanks and DeSelm 1963). Menzel (1954) found that cesium uptake is inversely proportional to the quantities of available potassium for the plant. Thus, i t has been demonstrated that increase in exchangeable potassium and the clay fraction of the soil (Squire and Middleton 1966), increase in available potassium, addition of calcium carbonate (Evans and Dekker 1966), and additional potassium chloride (Walker et al_. 1961), al l decrease uptake of cesium by plants. 8^Sr has a h a l f - l i f e of 64 days, is not so hazardous as ^ S r ( h a l f - l i f e of 28 years), and hence is more convenient to use in experi-mental work than 9 0 S r . 8 5 S r is a member of the alkaline earth group and is similar to calcium in its behaviour in soils (Shultz 1965), plants (Collander 1941, Klechkovskii and Gulyakin 1958), and ecosystems (Alexahin and Ravikovich 1966). Its distribution in s o i l s , however, does not always correlate with that of stable strontium or calcium distribution since 20 radioactive strontium is more soluble. Sorption of strontium is increased with the rise of the pH; Juo and Barber (1970) found an increase in strontium sorption between the pH range 4-8. Under certain conditions strontium may form insoluble compounds (Juo and Barber 1969). Like cesium, the bulk of strontium released to the mineral soil tends to accumulate in the upper part of the soil profile (Walton 1963, Kwaratskhelia et a l . 1966, Polyakov et_ al_. 1966, Tyuryukanova ejt a]_. 1966, Gorham 1970, Jordon 1970). The bonding of strontium in the top horizons is attributed to their s i l i c a t e clays. Polyakov et al_. (1966) also found that the i l l u v i a l horizons 90 are very efficient in accumulating Sr. Accumulation in the i l l u v i a l horizons results from the changes in the reaction of soil solution moving from the upper to deeper horizons, the considerable storage of highly dispersed clay materials and sesquioxides acting as non-isotopic carriers, and the presence of loams which lense out into the soil mass and thus form a geochemical barrier to stop strontium from moving into the deeper horizons (Polyakov et aj_. 1966). Radiostrontium enters plants from the soil in relatively larger quantities than cesium (Romney et a l . 1957, Krieger et aJL 1966, Alek-sakhin ejt a.]. 1970). The factors controlling mobility of strontium in soils (eg. the intensity of precipitation, r e l i e f and the humus content of the soil) also influence plants' uptake of strontium. In greenhouse experiments, Kwaratskhelia e_t al_. (1966) found that nitrogen f e r t i l i z e r s (in the form of ammonium sulphate), rotted manure, and liming lead to decreasing strontium uptake from s o i l s . Strontium uptake is also less intensive when Ca content of the soil or nutrient solution is higher 21 (Friederiksson et al_ 1959, Romney et al_ 1959, Fowler and Christienson 1959, Balcaretal_. 1969). Russel and MiIbourn (1957) and Comar et al_. (1957) however, found Ca to have no influence on Sr uptake. Compared with cesium, strontium is relatively immobile in plants. A considerable amount of cesium is rapidly transferred to the wood, cortex and roots between two to four weeks after tagging (Olson 1965). However, sixteen months after inoculation of loblolly pines (Pinus taeda L.), Dayton (1970) found that radiostrontium concentrations below the inoculated areas were relatively low, and in large roots were barely detectable. Similar slow basipetal-transfer rates have been reported in other plants by Bukovac and W.i!ttwerS(il>957) According to Hand-ley et al_. (1967) and Handley and Babcock (1970), 8 5 S r tends to move acropetally into contiguous new growth and basipetally into untreated old growth in about the same amounts from the site of f o l i a r contamination. Handley and Babcock (1970) demonstrated also that cesium moves predomi-nantly into new growth. Alexahin and Ravikovich (1966), however, found acropetal distribution of strontium and calcium in above parts of trees. Thus the concentration of strontium and calcium in the lower parts of trees (leaves, branches and bark) is greater than in the upper ones. The reverse is true for the root system: the roots in the top horizons contain more strontium and calcium than those from lower layers. Olson and Crossley (1963) have demonstrated that radiostrontium leaches more slowly than radiocesium from leaf l i t t e r . But Jordan (1970), 85 working with tropical s o i l , showed that 33 percent of Sr and 27 percent 134 of Cs that were applied to the rainforest plots moved out of l i t t e r after six months. This discrepancy is probably due to the differences in the rate of decomposition and mineralization of the l i t t e r studied. In the same study, Jordon found that 0.57% and 0.32% of the total 8 5 S r 134 and Cs, respectively, had moved through the five-inch depth in the s o i l . CHAPTER 3 THE RESEARCH AREA AND THE EXPERIMENTAL PLOTS 3.1. The research area The study area is located on the University of British Columbia (UBC) Research Forest, approximately 6 kilometres (km) north of Haney (Maple Ridge Municipality) and 60 km east of Vancouver. The geology, so i l s , topography, drainage, vegetation and climate of the forest have been described by Keser (1960). The area is characterized as equable (marine) mesothermal humid to rainy climate (Krajina 1969). January, with a mean monthly temperature of 1.1°C, is the coldest month, while July and August (the hottest months) have a mean of 16.6°C. The total annual precipitation is about 2280 mm. Most of the precipitation occurs in November, December and January. The driest months are June, July and August. The weather recorded (at the D.O.T. Station nearest to the experimental plots) during the study period is shown below (Figure 1 and Figure 2). 3.2. Description of the experimental plots Four experimental plots were selected in the south portion of the UBC Research Forest (Figure 3) in a 40-year old secondary forest characterized by a co-dominance of Coastal Western Hemlock and Western Red Cedar. Klinka (personnal communication 1972) has designated the 23 Figure 1. Monthly mean temperatures during the experimental period (July 1971-July 1972). Figure 2. Monthly precipitation during the experimental period (July 1971-July 1972). Figure 3. Location of the radioisotope experimental plots, Legend:L Plot #1 2, Plot #2 3, Plot #3 4 , Plot #4 OT-) Orthic Polystichum BfiBlechnum-Rubus \T Vacci ni um-Lysi chi turn 2 o m 26 area as belonging to the Orthic Polystichum ecosystem type, although some portions of the Degraded Polystichum type may be found. The characteris-tics of these ecosystem types are summarized below (Table 2). The f i r s t three plots were selected and fenced in the summer of 1970. A wooden cat-walk was constructed on each plot to reduce tramping of the forest floor during sampling. These plots were l e f t until the summer of 1971 to allow the forest floor to recover from any damage incurred during fencing and the construction of the cat-walks. The fourth plot was located and fenced during the summer of 1971. The f i r s t plot (hereinafter referred to as Plot 1) was about 161 square metres in area. The tree layer consisted mainly of western hemlock (Tsuga heterophylla (Rafn.) (Sarg.), western red cedar (Thuja  plicata Donn), clusters of vine maple (Acer circinatum Pursh) and paper birch (Betula papyrifera Marsh.). The ground was not completely covered vegetatively. The ground vegetation consisted Of western sword-fern (Polystichum muni turn (Kaulf. Presl.)) and mosses (Dicranum scoparium) Hedw., PIagiomnium insigne (Mitt.) Koponen, Rhytridiadelphus 1oreus (Hedw.) Warnst., Leucolepsis menziesii (Hook.) Steere, Hylocomium splendens (Hedw.) B.S.G.) which grow mainly on decaying logs. Neckera douglasii Hook., Isotheciurn stoloniferum (Hook.) Brid and Scapania bolanderi Aust. are epiphytic on the vine maple trees. Plot 1 was selected because of the abundance of the epiphytic mosses on the stems of the vine maple trees which were growing underneath a dominant western hemlock overstorey. The main objective on this plot was to study whether the epiphytic mosses receive nutrients from throughfall precipitation coming from the hemlock tree crown. 27 TABLE 2 E cosy sterna t i c units and their distribution in the research site (after Klinka's preliminary draft 1972) Eocystem Type Characteristi cs Orthic Polystichum Degraded Polystichum Blechnum Rubus Vaccinium Lysichitum Subzone Dry More or less both dry and wet Land Type Glacial Drift General Grouping Hygrophytic species combination, concave r e l i e f . Presence of seepage, deep s o i l s . High productivity. Spring water, swamp for-mation, out-wash terraces Land Form Lower slope. Outwash terraces 130-365 m. Seep-age permanent and moving depending upon slope, fast on slopes. Lower slopes 140-530 m Seepage temporary Lower slopes terraces, valley bottoms seepage slow Depressions gently slop-ing. Seep-age at soil surface 48-305 m. Soil Series 1 Capilano (CP), Bose (BO), Boosey (BY) Boosey (BY) Jackman (JM) Judson (JN) Continued 28 TABLE 2 - Continued Characteristics of the soil series: CP: Parent material - Glaciofluvial (outwash and ice contact); Texture - Gravelly loamy sand, well s t r a t i f i e d ; Classification - Orthic Humo-ferric Podzol; Drainage - well; Slope - 5 to 20%; Coarse fragments - 0 to 5% BO: Parent material - Glaciofluvial <150 cm over glaciomarine; Classification - Mini Humo-ferric Podzol; Drainage - well to moderately well; Slope - 5 to 20%. BY: Parent material - Glaciofluvial <150 cm over glaciomarine; Classification - Gleyed Mini Humo-ferric Podzol; Drainage - imperfect; Slope - 0 to 20. JN: Parent material - organic; Classification - Terric Mesisol; Drainage - very poor; Slope - 0 to 2% JM:- Parent material - Glaciofluvial <150 cm over glaciomarine; Classification - Rego Humic Gleysol; Drainage - Poor; Slope - 0 to 5%. 29 The second plot (Plot 2) had an area of about 79 square metres. The vegetative cover was similar to that of Plot 1 except that paper birch was lacking and salal (Gaultheria shallon Pursh) was present. There was also a relatively large carpet of Hy1ocomiurn splendens under one of the hemlock trees. The selection of this site was based upon its similarity to Plot 1, for which i t represents a replicate. Plot 3 was situated in an opening and had an area of about 116 square metres. The ground was covered almost completely with mosses. The moss species identified were PIagiomnium insigne (occupying the;greatest portion of the forest floor area), Hylocomium splendens (mainly around the base of trees), Eurynchium oreganum (Sull.) Jaeg. & Sauerb., Leucolepsis mengte^i&can^ Maikeiethe':ro.ther-rp'tots ;al:l'-the mosses seemed to grow on decaying wood. There were also some sword fern, deer fern (Blechnum spicant (L.) Roth.) and s a l a l . The tree layer consisted mainly of western hemlock and some paper birch. On this plot the aim of the study was to find the probable distribution of nutrients in through-f a l l precipitation on the forest floor, the concentration of radionuclides by various ground mosses, and the penetration of radioisotopes into the soil beneath various species of moss and in the absence of moss. Plot 4 was situated immediately adjacent to Plot 3. The ground was not completely vegetated, being occupied in part by mosses and ferns. The tree layer was again, western red cedar, western hemlock, paper birch and thickets of prostrate vine maples which were hosting the epiphyte, Isothecium stoloniferum. This plot was selected on the basis of the prostrate vine maples in order to bute nutrients to stemflow waters nutrients from this source. 30 study whether the bark tissues contri-and also whether the epiphytes obtain CHAPTER 4 METHODS 4.1. Radiotracer technique 134 A tracer technique, involving a double labelling with Cs QC and Sr, was used in the study. The radioisotope tracer technqiue has been used as an aid in finding solutions to d i f f i c u l t and complex problems in ecosystem studies. Applications of this technique in the plant and soil sciences and in several aspects of forestry research have been reviewed by Spikes (1963) and Fraser and Gaertner (1966), respectively. In investigations involving biogeochemical cycles, known quantities of an isotope (or isotopes) are introduced into one part (or compartment) of an ecosystem and subsequent sampling provides an estimate of d i s t r i -bution and accumulation within the various compartments of the total ecosystem. For this study, the isotopes were introduced into the eco-system through the stem of trees. Tagging of plants can be accomplished by a variety of techniques which have been reviewed by Fraser (1956, 1958), Sudia and Li nek (1963) and Olson (1968). Radionuclides in solution can be introduced into the aerial portions of a plant by one of the following methods: liquid drop applications, spray application, leaf flap methods, stem-well methods, stem injections and wick methods. Radionuclides may also be applied 31: 32 to plants through the root system (Sudia and Linck 1963). For a f u l l -size tree, inoculation can be achieved by methods involving d r i l l i n g of holes into the wood,.foliar spraying, wrapping of gauze around branches of trees, or the stem-well technique. In this study a technique involving stem-drilling and the use of transfusion bottles was adopted. The technique was f i r s t used by Petty and Williams (1965) and later modified by Dayton (1970); some modifications have also been made in this study. 4.2. Inoculation of trees on the experimental plots On J u % 16, 1971, two dominant western hemlock trees (one each 85 on Plots 1 and 2) were each inoculated with 8 millicuries (mc) of SrClg (in 0.5 N HCl) and 4 millicuries (mc) of 1 3 4 C s C l (in 0.5 N HC1) diluted in 300 m i l l i l i t r e s (ml) of water. The radiometric purity of each isotope 85 134 was 99+ percent while the specific activities of Sr and Cs were 10.0 m'c/mg and 49.0 nic/mg, respectively. The tagged tree on Plot 1 measured 25.65 centimetres (cm) in diameter breast height (dbh) and about 26.5 metres (m) in height. The tree on Plot 2 was 27.7 cm dbh and about 28 m t a l l . Two hemlock trees of similar size (24.5 cm dbh and about 26 m in height) on Plot 3 were each inoculated on July 22, 1971 with the same amounts of isotopes as used for the trees on Plots 1 and 2. Labelling of five prostrate vine maple stems (with diameters ranging from 4.6-6.9 cm) on Plot 4 was done on July 30, 1971. Two of them, which were single 85 134 stems, were each inoculated with 1.0 mc Sr and 0.3 mc Cs dissolved in 75 ml H^ O. The remaining three were in a group which was labelled with a single application of 3.0 mc Sr and 0.9 mc Cs in 225 ml FLO. 33 4.2.1. The inoculation procedure. Plexiglas spouts were constructed consisting of 7.5 cm square plates of 0.25 cm thickness which bent to conform to the diameter of the tree being labelled and which had a 1.5 cm (outside diameter) plexiglas pipe angled upwards at about 45°. Four spouts were used on each hemlock tree, one on each cardinal direction at a height of about 2.5 m. The bark was smoothed and the spout made secure with Dow Corning silicone sealant and screws. The tube was f i l l e d with water and a hole of 8 cm in depth was made (through the tube) into the sapwood of the tree by means of a long-bit power d r i l l . The hole was flushed with water to remove chippings. The four spouts were connected by small bore plastic tubing to a 500 ml transfusion (saline) bottle which was suspended 1 m above the spouts. The entire system was set up free of a i r bubbles, and after checking for leaks and satisfactory uptake of water, the transfusion bottle was exchanged for one containing the isotope in 300 ml of water. q The isotopes were introduced into the transfusion bottles in breakseal ampules enclosed in plastic gauze bags, the ampules were broken with a steel rod and the water added. All glass fragments were retained by the plastic gauze bags. This method was found to be rapid, safe and resulted in minimum external contamination. All handling of ampules were performed using long-handled tongs and the use of lead and water shielding. After complete uptake of the radionuclide solution, the inoculation bottle was removed, rinsed with 500 ml of water and returned to its position on the tree for further uptake. 34 A similar technique was used for the inoculation of the vine maple trees on Plot 4 except that each stem was inoculated only on one side. The inoculation bottles were rinsed with 100 ml of H20 per 1.3 mc 85 134 activity of Sr and Cs used for the inoculation. Uptake of the isotopes by the hemlock trees was very fast, occurring in less than 12 hours. On the other hand, the movement of the isotopes into the vine maple trees was slow, ranging from about four days to approximately one week. 4.3. Experimental Design and Sampling 4.3.1. Study of natural radioactivity of mosses. One-quarter metre square quadrats of mosses were taken between trees in different areas at the UBC Research Forest and the UBC Endownment Lands (Figure 4) in August 1971. Each quadrat of moss collected was put into a plastic bag and taken to the radioisotope laboratory (at UBC Faculty of Forestry, 137 Vancouver) for radioassay of Cs. 4.3.2. Somer,nutrient sources forsepiphytic mosses Leachate from stem tissues as a source of nutrient. This study was conducted on Plot 4. A spiral flow gauge was f i t t e d , before inoculation, to each of the five inoculated prostrate vine maple stems and one other unlabelled stem (30 cm from the group of the three labelled stems) by a method similar to that of Cole and Gessel (1968). A piece of weather stripping was attached to a smoothed portion of each stem by using rubber cement. The lower end of the stripping was directed Figure 4. Sampling sites for Cs fallout study. Legend: 1.) UBC Endownment Lands 2) Y-Camp 3) Kimmins study area (also research area for the main study, cf. Figure 3) 4) Mark Wier 5) Blaney Lake 6) Eunice Lake 36 into a plastic container which led into an ion exchange resin column to collect radionuclides in the stemflow water (Figure 5). The exchange columns were specially designed to f i t the standard test tubes (25 mm diameter x 150 mm length) used in the s c i n t i l l a t i o n counter. They could also be cleaned with 2 M HC1 after sampling and re-used. Each collector was set up so that the part of the stem below i t received neither stemflow or throughfall from the upper part of the inoculated trees. In May 1972, the stemflow collecting systems on three of the inoculated stems were modified to collect leached radioisotopes and total volume of stemflow waters from specific surface areas of the stems. Samples of epiphytic mosses were taken from the areas below the stemflow collars and away from the zones of inoculation from September through November 1971 and in July 1972. Resin columns were collected and replaced in October and November 1971 and in March and July of 1972. Throughfall as a source of nutrients. Mosses were sampled on the stems of the vine maple trees growing under the canopy of the inoculated hemlock trees on Plots 1 and 2 between September and November 1971. Three vine maple stems on Plot 1 were selected in May 1972. All the epiphytic mosses on each stem were removed except those growing on a length of about 30 cm (in the lower half of the stem). A stemflow collector was constructed below each zone of the remaining epi-phytic mosses to collect the total volume of water and radioisotopes after passing through the mosses. The moss portions on the stems were harvested 85 134 in June 1972 to assay for Sr and Cs activity. At the same time the resin columns were replaced with another set, and the volume of water Figure 5. P l o t #4 showing the i n o c u l a t e d vine mapfte trees and stemflow c o l l e c t i n g systems. 37 38 collected was measured. Another collection of resin columns and water were made in July 1972 to measure the concentrations of the radionuclides per unit volume (in absence of the mosses). 4.3.3. Patterns of distribution of throughfall leachates on the forest floor. The experiments reported here were carried out in Plot 85 134 3. To determine the patterns of distribution of Sr and Cs leachates in throughfall, fifteen collectors were installed prior to the tagging of trees under and at the margins of the canopies of the two inoculated western hemlock trees in the patterns shown in Figure 6. Each collector consisted of a 12.5 cm diameter plastic funnel (with a nylon-wool f i l t e r ) connected to an ion-exchange resin column. The collector was held one metre above the ground level by means of a metal support (Figures 7 and 8). Monthly samples were taken from September to November 1971 and in March 1972. No samples were taken between December and February because of the low winter temperatures. The low temperatures made the r e l i a b i l i t y of March samples questionable since the resin columns were frozen. In late April 1972, the resin columns were replaced with plastic containers to measure the throughfall volumes. This was done to test the relationship between total leached activity in throughfall and the volumes of through-f a l l at the same sampling spots. Throughfall volumes were measured for four individual storm fronts from May to July 1972. 4.3.4J Concentration of radionuclides by various ground mosses. The understorey vegetation (mainly mosses) on Plot 3 was sampled at the same time as the resin columns. Samples were taken very close to the positions of the resin-column collectors so that comparisons could be Figure 6. Layout of the 15 throughfall collectors on Plot #3. Legend: Inoculated hemlock trees © Positions for collectors • 39 Figure 7. P l o t #3-showing the i n o c u l a t e d hemlock trees and some of the t h r o u g h f a l l c o l l e c t o r s . Figure 8. A t h r o u g h f a l l (or stemflow) c o l l e c t o r . made between the amounts of radionuclides intercepted by the vegetation and the total activities in the throughfall. 4.3.5. Penetration of radioisotopes into the s o i l . Prior to 2 the inoculation of the treesj 0.06 m quadrats of ground-dwelling mosses were taken from Plot 3 and counted to give a measure of pre-inoculation background activity. In April 1972, soil cores (5 cm in diameter and 15 cm in depth) were taken at specific distances from the trunk of the inoculated trees on the plot to study the distribution of radionuclides in the undisturbed condition and in the absence of mosses. 4.3.6. Sampling of the inoculated trees. Small branches from the inoculated hemlock trees were sampled periodically (using a r i f l e ) in the middle crown areas. Stem cores were taken from the inocu-lated vine maples on Plot 4. 4.4. Laboratory Work The samples of epiphytic mosses and the understorey vegetation were air-dried in the laboratory and carefully separated from l i t t e r , soil and other extraneous substances. This was not easy in some moss species. For example, in PIagiomnium insigne, i t was not possible to separate the "root system" completely from humus. The needles of the small branches from the hemlock trees were detached by air-drying in plastic bags for about a week or by oven-drying in paper bags for a few hours. The twigs were separated from the needles and cut into small pieces. Samples of twigs and needles were taken from each lot. The stem cores from the vine maple stems were air-dried. 42 Each soil core was analysed as follows: Moss (where applicable) LF - mixture of freshly-fallen l i t t e r layer and the fermentation layer H - humus substance layer Mineral soil layer (top 3 cm) For the, humus and the mineral soil layers, samples were taken at every centimetre of depth. Mean values were then calculated to represent either the humus or the mineral soil layer. All the above samples were counted in special vials with a s c i n t i l l a t i o n counter (described below) 85 134 for Sr and Cs using the appropriate window settings. Samples from the soil cores were counted for 90 minutes with 60-minutes background counts while the vegetative samples were counted for 60-minutes with 30-minutes background counts. After counting, the height of the sample in each vial was measured. Samples were then over-dried (105°C) for 24 hours and weighed. The moss quadrats sampled for studying natural radioactivity were oven-dried for about 72 hours after removal of extraneous material. They were ground to a homogeneous powder and counted in standard test 137 tubes (25 x 150 cm) for Cs for 90 minutes with a 60-minute background count. The weight and the level of each sample in the test tube were measured. The heights and weights were used for geometry and weight correction respectively. The counts for the samples were also corrected for radioactive decay, background counts and machine efficiency. Activity .43 of the soil and the vegetative samples were expressed as microcuries per gram. 4.4.1. The Scintillation Counter. The s c i n t i l l a t i o n counter used was a Picker Nuclear Autowell II (with an automatic 100 capacity sample changer) with a Twinscaler II (Model 644-125). The detector was 3D x 3 in (7.62D x 7.62 cm) Nal(Tl) crystal with 1 1/8D x 2 in. (2.86D x 5.08 cm) well, with a 3-inch lead shield. Since autowell has a 2-channel analyser i t can simultaneously measure two radioisotopes in a single sample. CHAPTER 5 RESULTS AND DISCUSSIONS 137 5.1. Cs fallout activity levels of mosses 137 The biomass and Cs activity levels of mosses at the UBC Re-search Forest and the UBC Endownment Lands presented in Table 3 show high biomass values (dry wt/0.06m ) for Sphagnum squarrosum Crome and Rhyti- diadelphus loreus, and the highest activities (pCi/g dry wt) in practically a l l cases, for Plagiothecium undulatum. Activity levels of the three mosses (Mnium glabrescens, P. undulatum and j*. loreus) which were present in a l l five of the locations were analysed using Analysis of Variance and Duncan's New Multiple Range Test. On a per graiiin basis, there were no significant differences in the levels of activity of the mosses in the four locations at the research forest. The activity levels in each of the research forest locations were, however, significantly different (at the 5% level) from those of the Endownment Lands. Differences in 137 the mean concentration of Cs for a l l sites between P_. undulatum and M, glabrescens were insignificant (at the 5% level) but the mean of either M. glabrescens or P. undulatum differed significantly (at the 5% level) from that for JR. loreus. These results are presented on Tables 137 2 4 and 5. The amount of Cs deposited per unit area (m ) of moss was less than that which was deposited in each of the areas of the research forest (Table 3 and 5), though, the biomass values of mosses per unit area were higher at the Endownment Lands than at the research forest (Table 3). 44 TABLE 3 1 37 Cs fallout activity of mosses in the UBC Research Forest and Endownment Lands (based on 2 single quadrats for each moss). Sampling date: August 1970. Location Y Camp Alt i tude (m) 46 Mark Wier 152 Kimmins 1Study Area 168 Estimated mean annual precipitation (mm) 2110 2286 2286 Moss species £. oreganum I_. stoloniferum M. glabrescens P. undulatum JR. loreus E. oreganum H_. splendens I. stoloniferum M. glabrescens P_. undulatum R. loreus S_. squarrosum £. oreganum H_. splendens M. glabrescens P_. undulatum R. loreus Biomass^ q/0.06m^  1 37 0 7Cs activity level  pCi/g pCi/m^ 8.5 + ^.3f 19 + 0.7 2576 7.9 + 0.1 38 + 8.5 4832 8.6 + 1.6 40 + 3.2 5440 6.0 + 1.7 58 + 1.8 5552 14.5 T 0.8 27 + 1.1 6240 6.7 + 0.6 36 + 6.0 3808 7.0 T 0.3 28 + 4.6 3088 6.4 + 1.4 21 + 2.1 2160 4.3 T 0.8 59 + 4.6 4048 8.9 + 1.9 26 + 5.0 3696 9.1 + 1.0 22 + 1.8 3120 8.5 + 1.4 10 + 0.7 1360 10.1 + 0.6 33 + 2.8 5328 9.7 T 0.8 27 + 0.7 4192 9.0 T 0.2 43 -T 1.1 6080 9.9 + 0.1 61 + 0.4 9536 14.7 + 0.5 43 + 8.5 10112 continued TABLE 3 - continued Estimated Location Altitude (m) mean annual precipi tation (mm) Moss species Biomass? q/0.06m 1 "37 Cs activity level pCi/g pCi/m2 Blaney 343 2670 H. splendens 9.3 + 0.9 28 + 0.4 4166 Lake M. glabrescens NA 38 + 0.4 NA P. undulatum^ 4.3 86 5917 R. loreusl 9.4 31 4662 *S. bolanderi -j 10.1 + 1.0 33 + 3.5 5333 S. squarrosum 30.0 62 29760 Eunice 482 3050 H. splendens NA 24 +.1.1 NA Lake I. stoloniferum NA 32 + 4.6 NA M. glabrescens 9.8 + 0.7 43 + 0.4 6742 P. undulatum 7.3 + 2.0 75 + 0.7 8760 R. loreus 9.0 + 1.3 26+1.8 3744 S. squarrosum 17.6 + 2.3 54+1.8 15206 Endownment 30 1475 M. glabrescens 8.0 + 1.3 15 + 1.4 1920 Lands P. undulatum 9.2 + 1.0 19+1.8 2797 R. loreus 17.8 + 0.5 16 + 1.4 4557 Average activity (all locations) 36.7 6025 single sample *liverwort NA - not available f - standard error TABLE 4 Comparison of fallout activity levels of three mosses (mean of 5 locations) 137 Moss P_. undulatum M. gl abrescens R. loreus Average activity Biomass?  g/0.06m 8.2 + 0.3^ 7.9 + 0.3 13.0 + 0.4 Cs activity level pCi/g dry wt pCi/m 48 +.2* 6298 40 + 2* 5056 27+1 5616 38.3 5657 f - Standard error * - Homogeneous samples according to Duncan/s New Multiple Range Test 48 TABLE 5 Comparison of amounts of fallout activity in 5 locations (mean of P_. undulatum, NL gl abrescens and R. loreusT Location UBC Endownment Lands Y Camp Mark Wier Kimmins' Study Area Eunice Lake Average activity Biomass?  g/0.06iT) 11.6 + 0.8^ 9.7 + 0.7 7.4 + 0.5 Estimated mean annual precipi tation (mm)  1475 2110 2286 137 11.2+0.5 2286 8.7 + 0.4 3050 Cs activity level pCi/g dry wt pCi/m^ 17 + 0 41+2 i 35 +.3 i 49 + 2 i 48 + 4 38.0 ** ** ** 3155 6363 4144 8781 6682 5825 f - standard error ** - Homogenous samples according to Duncan's New Multiple Range Test 49 Precipitation has more influence on radionuclide fallout de-position (van der Westhuizen 1969, Ritchie et aK 1970) than any other factor, though precipitation, latitude and elevation, being correlated, interact to control the amount of fallout radionuclide that is deposited in an area. The concentration of fallout radionuclides in plants, however, depends on species and the growth habits of plants (Gorham 1959, Kline 1970)&and is said to show a general decrease with decreasing latitude (Lockhart et al_. 1965, Kline and Odum 1970), elevation (Kline and Odum 1970, Ritchie et al_. 1970) and amount of rainfa l l (Pelletier et al_. 1965, 137 Roser and Cullen 1965, Kline and Odum, 1970). Comparison of activity 2 levels (uCi/g and yCi/m ) of the 3 moss species from the study areas (Table 3 and 5) supports the existing evidence in the literature that 137 precipitation is an important factor controlling the amount of Cs deposited. Since the annual precipitation of the research forest where samples were taken was greater than that of the Endownment Lands (table 3), 137 the lower levels of Cs activity of the Endownment Lands samples are expected. The unexpected non-significant differences between the sample means of the locations within the research forest may be due to the small number of samples taken relative to the great variability of input of chemicals to the forest floor in throughfall precipitation (Kimmins, unpublished manuscript). 137 The Cs concentration values reported by Kline and Odum (1970) in Puerto Rico (Table 6) are greater than those obtained in the present study due possibly to differences in precipitation and the growth habit of the moss species involved (Tables 3 and 6). Kline and Odum (1970) 50 sampled epiphytic mosses (filamentous hanging mosses) which are known to have a much greater abi l i t y to absorb radionuclides than ground dwelling species (Odum ejt aj_. 1970, Kline and Odum 1970) which were the subject of the sampling in the present study. We should, therefore, expect higher levels of activity with epiphytic mosses in British Columbia than those reported in Tables 3, 4 and 5 for the ground-dwelling mosses. The values for the ground dwelling species of the present study (36.7 pCi/g dry wt) are similar to those (35.8 +3.7 pCi/g dry wt) obtained for ground-dwelling mosses (mostly Hylocomiurn spp. and Rhytidiopsis spp.) of a cedar-hemlock stand in Washington (Rickard 1971, Table 6), although Rickard had earlier (1966) reported a mean value of about 60 pCi/g dry wt for mosses (mainly Rhytidiopsis robusta) in the same vicinity. From this data, i t could be inferred that Rhytidiopsis sp. intercept more fallout than Hylocomium sp. Lower levels of activity found in Hylocomiurn sp. (24-28 pCi/g dry wt) in this study are probably due to rapid loss of the intercepted radionuclides from the decomposing older segments of the moss. These older segments have higher concentrations of a l l elements except K as compared with the younger segments (Tamm 1953, Riihling and Tyler 1970). This probably indicates rapid K loss from these segments through leaching and or translocation into the new segments. Since Cs or K leaches out of plants more rapidly than most elements and even more so in older tissues, leaching would probably be the cause of the low Cs or K concentrations in the older moss segments. i TABLE 6 137 . . Values of Cs natural fallout activity in mosses from other sources Location Effin Forest (Puerto Rico) Cascade Mountain of Washington Packwood vicinity La Wis Wis Summit Creek Ogotoruk Creek Valley, Alaska Lati tude 18°N 48°N 48°N 48°N 68°N Elevation _JlD) 914 457 454 600 Precipitation (mm)  5080 1472 1472 1472 203 Acti vi ty  Moss type (pCi/g dry wt) 61.7 - 210 Epiphytic mosses Mainly Rhytidiopsis robusta 60 Mainly Hylo- 35.8 + 3.7 comiurn spp. and Rhytidiop- sis spp. Mainly Hylo- 33.7 + 2.8 comi urn spp. and Rhytidiop- sis spp. Sphagnum spp. 19.1 +4.1 Source Kline and Odum (1970) Rickard (1966) Ri ckard (1971) Rickard (1971) Rickard et a l . 7J965) 52 5.2. Primary nutrient sources for epiphytes 5.2.1. Epiphytic mosses as f i l t e r s of crown-washed nutrients. The results obtained from the experiment conducted to show that epiphytic mosses are efficient at sorbing chemicals from throughfall are shown in Table 7. It is apparent from these results that mosses are indeed highly efficient concentrators of leachate chemicals. But whether these nutrients enter into the tissues of the epiphytic mosses or are merely adsorbed on their surfaces is another question. Leaching studies made with Spanish moss (Tillandsia usneoides L.),^ an epiphyte, by Elder and Moore (1965) showed that various degrees of washings with water or 0.5 137 N KC1 did not remove Cs and other radionuclides from this plant. They concluded that Spanish moss actively binds and incorporates into its tissue the elements i t adsorbs on i t s surface. Riihling and Tyler (1970) have demonstrated with Hylocomium splendens that elements which are sorbed by i t are retained in its tissue. From this evidence we may assume that the nutrients which the epiphytes f i l t e r from throughfall or stemflow are retained and utilized by them. Tamm (1953, 1964) has claimed that some ground-dwelling mosses and a l l epiphytes depend for their nutrients on substances that are leached out of tree crowns. However, observations have shown that some epiphytes can thrive without the influence of tree canopies. According to Benzing and Renfrew (1971) dwarf cypress trees (Taxodium distichum (L.) Rich.) supporting large colonies of twisted a i r plant (Tillandsia ^Spanish moss is an epiphyte, not a true moss. It is a flowering plant belonging to the family Bromeliaceae. TABLE 7 Efficiency of epiphytic mosses in f i l t e r i n g radionuclides in through-f a l l and stemflow waters Biomass of moss (g) Calculated surface area occupied by moss (sq cm) Total activity washed through moss (pCi/10 5) 85 Sr 134 Cs Total activity picked by moss (yCi/105) 85 Sr 134 Cs Expected activity picked by 1 sq cm of moss (uCi/10 5) 85 Sr 134 Cs Filtering e f f i ci ency of moss [%) 134 85 Sr Cs Tree 1 moss 5.42 1020 11100 699 7308 369 7.17 0.36 66.4 52.8 Tree 2 moss 7.03 1530 14732 880 7892 110 5.16 0.07 53.6 12.5 Tree 3 moss 4.50 962 22560 2214 16680 1574 17.34 1.64 73.9 71.1 cn CO 54 circinata Schlecht.) in Florida have very sparse foliage which are present only in the growing season, and that there are many epiphytes in the forest which have no living branches above them at a l l . This contradicts the idea that tree crowns are the main source of nutrients for a l l epiphytes. 85 Reference to Table 7 shows that Sr was sorbed by the epiphytes 134 involved in the present study in relatively larger quantities than Cs. This is in agreement with Bell's (1959) finding that living Sphagnum moss shows preferential absorption of ions of higher valencies from solutions resembling natural waters in composition. According to Bell (1959), and Ruhling and Tyler (1970), different species of Sphagnum have been demonstrated (by Williams and Thompson (1936), Anschutz and Gessner (1954) and Puustjarvi (1955)) to act as ion exchangers. The manner in which the epiphytic mosses sorb elements from water is probably similar to that of Sphagnum moss. 5.2.2. Leachates from the stem as a source of nutrients for  epiphytes oc I on Leaching of Sr and Cs from vine maple stems. Carlisle e_t al_. (1967) have provided data for the quantities of nutrients which are added to stemflow waters of a sessile oak (Quercus patraea (Mattuschka) Liebl.) woodland. The amounts of Ca and K added annually to these waters were stated to be 1.90 kg/ha and 1.46 kg/ha respectively. The origin of the nutrients is doubtful, although i t was said that leaching of elements from the bark tissue could possibly account for some of the nutrients in these waters. Table 8 presents the results of the experiment TABLE 8 8 5 S r and 1 3 4 C s in stemflow waters of inoculated vine maple trees Tree #, Sampling date Activity, yCj'/HO k5 85 Sr 134 Cs 8 5 S r / 1 3 4 C s (1:1 inoculum) assumed) Volume of ;S temf 1 ow water (ml) Activity/ml uCi/105 85 Sr 134 Cs Stemfl ow collection area ( Expected activity 1 sq cm of sterrir surface (yCi/ltr) 85 Sr 134 Cs October 26, 1971 #2 #4 #5 43 67 134 68 169 262 0.19 0.12 0.16 NA November 29. 1971 #2 #4 #5 290 19 2143 288 22 2142 0.31 0.26 0.30 NA March 3, 1972 #2 #4 #5 513 190 2472 128 22 1285 0.22 2.62* 0.58 NA July 5, 1972 #2 #4 #5 3172 821 19774 426 93 2857 2.26 2.68 2.10 275 935 1000 11.6 0.9 19.8 1.5 0.1 2.9 160 320 520 21.2 2.6 38.0 2.7 0.3 5.5 Continued TABLE 8 - Continued Tree #, Sampling date Activity, yCi'/WO 55 85 Sr 134 Cs 8 5 S r / 1 3 4 C s (1:1 inoculum assumed) Volume of stemflow water (ml) Acti vi ty/ml yCi/10*5 8 5 S r 1 3 4 C s Stemflow collection area (sq cm) Expected activity 1 sq cm of steirir surface (yCi/10 ) 85 Sr 134 Cs July 15, 1972 #2 #4 #5 1223 828 26928 214 137 5653 1.73 1.82 1.44 1300 1500 4000 0.9 0.6 6.7 0.2 0.1 1.4 160 320 520 7.6 2.6 51.8 1.3 0.4 10.9 NA = not available * = the relatively high ratio i s , probably, due to machine error cn 57 performed to test the hypothesis that the bark tissue contributes nut-85 134 rients to the stemflow waters. Both Sr and Cs were detected in the stemflow waters which were collected from the inoculated vine maple stems, suggesting that for vine maples of the particular age under study, leaching of the stem may constitute a significant source of nutrient loss. 85 I n i t i a l l y , Sr was leached out in relatively smaller quan-134 t i t i e s than Cs. This trend was reversed during the latter part of the study, however, due probably to the different rates of mobility and susceptibility to leaching of the two elements. Cs (or K) is said to move more "freely" in the plant than Sr or Ca (Levi 1968) since Cs (or K) is not strongly bound to exchange sites in the xylem as is Sr (or Ca). Sr (or Ca) movement in the xylem is therefore restricted because other bound cations are more readily replaced (Bell and Biddulph 1963). According to Tukey et al_. (1965) and Mecklenburg et al_. (1966), cations such as K, Rb, Sr, and Ca are leached from the plant by a process of ion exchange and diffusion involving exchange sites. Leaching of cations from foliage (and probably, the stem) is primarily a passive process, although some metabolites may be deposited upon plant surfaces through active process. Carbonic acid is f i r s t formed from CC^ from air and water on the plant's surface. Dissociation of the acid takes place and the released hydrogen ions exchange with cations on the cuticle (or bark) and cell wall exchange sites to form alkaline carbonates. The alkaline carbonates are either precipitated onto the surface of the plant or remain in the leaching solution and are washed off the surface by precipitation. 58 Ca has been demonstrated to be immobilized in the phloem as oxalate crystals (Fraser 1958) after its transfer from the xylem (Fraser 1958, Zimmermann 1960, Thomas 1967a). Samples of bark, wood, twigs, leaves and mosses were taken in July of 1972 from the vine maple stems to study the distribution of the radioisotopes therein. The purpose was to determine the concentration of radionuclides in the bark tissue in order to establish the relationship between bark concentrations and 134 bark leaching. The results, which are given on Table 9 show that Cs 85 was present in a l l the components studied while Sr was present only in the leaves and some of the moss and twig samples. The detection of 8^Sr in stemflow waters (which were sampled at the same time as the above vegetative samples) and i t s absence from the bark led to a further investigation. Samples were taken at various distances from the point of inoculation along one of the labelled vine maple stems to study the 85 134 distribution of Sr and Cs in the plant. Table 10 presents the 134 results. Whereas Cs was again detected in every stem component, the presence of 8^Sr was irregular. Two samples taken at adjacent points 85 85 may or may not contain Sr, which indicates that Sr was very unevenly distributed in the plant. o r The reason for the observed patchy distribution of Sr in stem components is not known. It may be suggested, however, that this was 85 due to l i t t l e tangential translocation of Sr from the ascent pathway. Tree 1 Tree 2 Tree 3 Tree 4 Tree 5 Tree 59 TABLE 9 oc 1OA Sr and Cs concentration in tissues of labelled vine maple trees (sampling date July 5, 1972) -4 Activity per gram (uCi x 10 /g) 8 5 S r 1 3 4 C s 1 Moss 9145 5475 Moss 29483 7083 Moss U 2292 Moss 2482 1218' Xylem U 209 Bark U 640 Moss 263 71 Moss U 28 Xylem U 101 Bark U 524 Foliage 121 166 Twi gs 4 T Moss 56 39 Moss 9 35 Xylem U 295 Bark U 837 Foliage 541 1088 Twig U 5 Moss 745 165 Moss 276 469 Xylem U 660 Bark U 2386 Foliage 2525 1824 Twi g 1354 487 * 6 . Moss 35 6 Moss U 40 Xylem U 1 Bark U 3 Foliage 19 12 Twi g U T U = undetected T = trace TABLE 10 Sr and Cs concentrations (yCi/10 per gm) in epiphytic mosses and a vine maple tree at various distances (cm) from the point of inoculation. (Sampling date: August 22, 1972.) ** 10 * 10 30 * 60 * 100* 1000* * 1150 100*UN 85 c Sr 1 3 4CS 8 5 S r 134 85 S r 1 3 4 C s 85 S r 1 3 4 C s 85 S r 1 3 4 C s 8 5 S r 1 3 4Cs 8 5 S r 1 3 4 C s 8 5 S r 1 3 4 C s Xyl en| 106 27 3720 994 971 347 1235 255 357 187 9 3 U 1268 1105 511 903 332 426 115 12 5 Bark^ 767 451 8030 3578 762 2300 3083 1258 1529 689 26 13 1158 424 U 5476 7463 2319 4302 1396 1950 730 U 16 Moss 52 1366 U 2008 U 757 190 195 U 42 Living r 2 1 U 3 twigs 11 1 11 2 Dead5' 1 1 twi gs 1 1 2 Old foliage 13 14 * ** = cm distance above point of inoculation = cm distance below point of inoculation U = undetected UN = unlabelled stem f = duplicate samples o 61 Contamination of. epiphytic mosses by stem  leachates ( 8 5 S r and 1 3 4 C s ) . Nutrients leached from stems may be a major source of nutrients for stem dwelling epiphytes. Table 11 shows that the epiphytes taken from the incoculated vine maple stems were contaminated by the radionuclides, and there was a general increase of radioactivity pr-O f mosses from September of 1971 to July 1972. Sr levels were i n i t i a l l y very low or undetected in the mosses but increased over the course of 134 the experiment. Cs, on the other hand, was detected from the f i r s t sampling date and increased steadily throughout the study. The general increase in the moss activity indicates that there was a continuous supply of radionuclides to the mosses and can be interpreted as indicating that the mosses were able to retain the radionuclides e f f i c i e n t l y . Losses of radionuclides from the mosses by leaching were not determined but the literature would suggest that such losses were probably small (Elder and Moore 1965, Svensson 1966). 5.3. Nutrients and epiphytic adaptation From a consideration of the data presented in the previous sections, i t may be said that epiphytic mosses and probably other epi-phytes u t i l i z e nutrients leached from the bark tissue of the "host" plant. Rain, f o l i a r leachates or dust will provide an additional source of nutrients for these plants. The relative importance of each nutrient source to the epiphytes will depend upon the morphology of the epiphytes and the availability of the nutrient source which is influenced by con-ditions such as the nature and the presence of overstorey trees, and the TABLE 11 Radioactivity (pCi/g) of epiphytic mosses on inoculated vine maple trees Sept. 16, 1971 Oct. 26, 1971 ..Nov. 29, 1971^* Jan. 28, 1972 July 5, 1972^ 85 S r 1 3 4 C s 85 S r 1 3 4 C s 8 5 S r : 1 3 4 C s 85c Sr 1 3 4Cs 85 c Sr 1 3 4 C s Tree # mosses 1 113 235 U 1289 119 U 3633 116687 15691 71805 914478 2948270 547548 708327 Tree # mosses 2 24 259 307 1992 369 2 4101 2335 39560 20062 248169 U 121757 229199 Tree # mosses 3 U 1755 U 2096 959 U 4907 1085784 9097 26932 26304 U 7101 2817 Tree # mosses 4 U 418 18 1055 338 U 305 98731 2406 2260 5598 892 3855 3517 Tree # mosses 5 32 226 U 2712 274 U 861 91592 1732 23509 27625 .74492 46852 16499 Tree # ** 6 62 118 124 361 480 703 1273 171 U 3504 1246 599 ** U = undetected = unlabelled stem f = two samples taken from different portions of the stem = tree was found to be dead on this date; increased in activity attributed to death of stem tissues. 63 susceptibility of the host to leaching. Epiphytes such as mosses which form mats close to the stem may u t i l i z e nutrients leached from the stem tissues as their primary source of nutrition. In terms of the nutrient cycle, epiphytes may play an important role by holding up nutrients obtained from the host (and other sources), at least temporarily. Thus nutrients which may be lost to other compart-ments of the ecosystem through leaching from the host tissue are retained in direct contact to the host by the epiphyte. For green stems (such as those of vine maple in this study) there is a possibility that these nut-rients would be reabsorbed through the bark of the host after release 85 134 by the epiphyte. Absorption of Sr and Cs through the green vine maple stems was not determined, but Riekerk (1967) reported a study by Kiseler using radio-phosphorus which showed that elements are absorbed through the bark, and Tukey et al_. (1958) have claimed that any part of the plant which can lose nutrients can also absorb nutrients. Thus, there may be a mutual nutrient exchange between the green stem tissue and the epiphytes, with the rate of the cycle depending upon the rates of elemental leaching and absorption by the host and the epiphytes. 5.4. Interspecific translocation of elements From Tables 9 and 11 we may deduce that the uninoculated stem in the clump of inoculated vine maples received some radionuclides from the inoculated trees. This is in agreement with the findings of Woods 45 and Brock (1964) and Woods (1970) which showed transfers of Ca and 32 P from red maple (Acer rubrum L.) donors (Woods and Brock 1964) and 64 3 2P, 4 5Ca, 8 6Rb and 3 5S from sand hickory (Carya pallida (Ashe) Engl. & Graebn.) and blackjack oak (Quercus mari1andica Muenchh.) donors (Woods 1970) to other species. Transfer was said to be achieved through exu-dation from the donor and absorption by the receptor species, through mutually shared mycorrhizal fungi, or through root grafts (Woods and Brock 1964). 85 134 The transfer of Sr and Cs to the uninoculated stem and the presence of these isotopes in samples taken 10 cm below the inoculation point (Table 11) indicate that the isotopes can move basipetally. However the activities below and above the inoculation zone show that downward translocation was comparatively slower than upward movement. Table 11 also shows that there was a general decrease of activity levels with distance from the inoculation point. 5.5. Nutrients in throughfall and forest floor nutrient dynamics 85 134 5.5.1. Sr and Cs activity levels in the inoculated hemlock 85 1^ 4 -4 tree needles.and twigs. The Sr and Cs activity per gram (pCix 10 /g) of the needles and twigs from the inoculated hemlock trees are illustrated 134 in Figures 9 and 10 respectively. The scale used on the Cs axis is pc pc double that of Sr for convenience in comparing the activities of Sr 134 134 and Cs, since the amount of Cs used for the inoculation was half that of 8 5 S r . 134 The peak activity of Cs in both needles and twigs occurred between January and March 1972 (241 days after inoculation) and dropped 65 t i l l the last sampling date (July 15, 1972). The rates of radiocesium movement have been studied by Witherspoon (1963, 1964), Auerbach et a l . (1964) and Kimmins (1970) in white oak (Quercus alba L.), yellow poplar (Liriodendron tulipifera L.) and red pine (Pinus resinosa A i t ) , respec-tively. In a l l these studies peak Cs activity in foliage was obtained within 40 days from the time of inoculation but the samples taken a month after inoculation in the present study showed low a c t i v i t i e s . Since no samples were taken between the middle of August 1971 and January 28, 1972, i t is possible that the peak activity may actually have occurred during this period, si Dargen''amounts1'of = Cs'were-leached in-through f a l l in October 6fuT.97T. thanotniea'nycoth^ictfllJec'tiJo'n >p6i9iwd (-Figure'oVl^'f-^HoweVer high total throughfall activity over a period of several weeks may not necessarily 134 reflect peak Cs activity in foliage since throughfall leaching is not solely dependent upon f o l i a r concentration. The duration and frequency of rain storms is of greater significance than total precipitation for the period. We should also not over rule the fact that the l i f e span of the foliage can affect the time for f o l i a r peak activity. The leaves of the tulip trees and the white oaks, respectively used by Auerbach et aj_. (1964) and Witherspoon (1964), being deciduous, have a shorter l i f e span and hence accumulate nutrients and gain weight early in spring whereas non-deciduous leaves achieve these throughout most of their f i r s t year of growth. For example, whereas Thomas (1967b) found 73% + 6 of 45 the total Ca inoculated into dogwood trees (Cornus florida L.) in the foliage of the trees one month after inoculation, Dayton (1970) did not detect the peak f o l i a r activity of radiostrontium (an analog of Ca) in loblolly pines (Pinus taeda L.) until 13 months after inoculation. Figure 9. Changes in activity of Sr in twigs and needles of inoculated hemlock trees (mean of 3 trees). Figure 10. Changes in activity of Cs in twigs and needles of inoculated hemlock trees (mean of 3 trees). 67 QC The highest Sr activity in the twigs was observed in July p c 1 OA 1972. There were decreases in Sr (and Cs) activities of the foliage and twig samples in May 1972 from the values obtained in April 1972. These may be attributed to heavy leaching of the radionuclides from the crowns by the high rainf a l l in May of 1972, or as Kimmins (1972) suggested, to the dilution effect of shoot and needle expansion. Kimmins 134 (1970) also found that greater quantities of Cs accrued in twigs than in the needles of red pine due, probably, to the greater susceptibility of leaves to leaching. While the samples of August 1971 and July 1972 85 had more Sr in the twigs than in the leaves, the opposite was true for the other sampling periods (January 28-Apri<l> 18, 1972). It would appear pc that Sr moves from the twigs to the needles during the f i r s t part of the growing season and with the loss of the older needles and possibly through leaching, the activity of the foliage drops. 134 85 5.5.2. The removal of Cs and Sr from.the tree crowns in  throughfall precipitation. The data for the removal of the radioisotopes in throughfall from the time of inoculation to the end of November 1971 are presented graphically in Figures 11 and 12. During this period about 134 85 0.6% of Cs and 0.025% of Sr used for the inoculation were removed to the forest floor by fo l i a r leaching. These figures are lower than 134 those reported by Witherspoon (1964) and Kimmins (1970) for Cs, and 89 that by Dayton (1970) for Sr. The lower values of the present study may be due to differences in duration of sampling or may be an evidence for resistance to leaching by trees in areas of high rainfall since the rainfall in the study area is higher than those areas of Witherspoon (1964), Kimmins (1970) and Dayton (1970). Figure 11. Distribution patterns of Sr in throughfall under inoculated hemlock tree canopy. Figure 12. Distribution patterns of Cs in throughfall under inoculated hemlock tree canopy. Figure 13. Patterns of throughfall water distribution under hemlock tree canopy. 69 O C "I OA 5.5.3. The pattern of throughfall input of Sr and Cs pc "i 04 to the forest floor. The distribution of throughfall Sr and Cs collected in relation to distances from the tree stem is presented in pc "I Figures 11 and 12. Both Sr and Cs show the same pattern. The radio-nuclide activities increased from about 0.25m from the stem to a peak at about 0.05m and then dropped with further distance from the stem. The depressions in the curves at 1.25m are due to the relatively open nature of the crown above the sample location for this distance. The mean throughfall volumes collected at the sampling spots are presented in Figure 13. In general, the throughfall volumes increase with distance away from the stem, although the small number of samples results in considerable variance. The pattern of throughfall nutrient distribution was further investigated in August 1972 by collecting throughfall water at equal intervals along two radii out from the stem under a 50-year old hemlock tree, similar in crown form to the labelled trees. The throughfall water samples were analysed for Ca, K, Na and Mg by means of atomic absorption spectrophotometry. The results of these analyses given in Table 13 and Figures 14 to 16 show that the spatial distribution of each of the elements 85 134 was similar to that of Sr and Cs, and that the pH, conductivity and throughfall volume increased with distance from the stem. The spatial pattern of the throughfall nutrients observed in this study is similar to that reported by Zinke (1962) for chemical elements in surface mineral s o i l . These results are consistent with the throughfall distribution inferred from soil moisture data by Voigt(1960b). TABLE 12 Volumes and chemical properties of throughfall water (under a single western hemlock tree) with respect to distance from the tree stem. Na K Mg Ca Distance from Conductivity, : : the tree stem Volume pH mmho/cm total total total total (m) (ml)- (25°C) . ppm mg ppm mg ppm mg ppm mg 0.5 98 4.1 1075 3.08 0.30 42.0 4.12 5.90 0.58 27.8 2.72 1.5 270 4.0 584 1.65 0.45 17.0 4.59 2.50 0.68 11.8 3.19 2.0 365 4.2 360 0.96 0.35 8.2 2.99 1.26 0.46 4.7 1.72 2.5 360 4.7 236 0.64 0.23 8.6 3.10 1.29 0.46 4.0 1.44 3.0 440 5.7 133 0.36 0.16 5.6 2.46 1.06 0.46 2.1 0.92 3.5 520 5.6 107 0.32 0.17 3.4 1.77 0.78 0.41 1.6 0.83 Figure 14. Patterns of K and Ca distribution under hemlock tree canopy. Figure 15. Throughfall water distribution under hemlock tree canopy. Figure 16. Changes of pH in throughfall water of hemlock tree canopy. 71 Distance from tree stem(m) 2 | 60*3} o u 8. 400J 4) E o > |20QJ 3 O 1 1 2 3 Disiance from tree stem(m) 72 Zinke (1962) attributed the pattern mainly to the differences between the effects of bark l i t t e r and the absence of l i t t e r in the opening between trees. According to Zinke (1962), the bark l i t t e r is usually very acid, low in bases, nitrogen and carbon, while the opposite is true with leaf l i t t e r . As a result, the soil close to the tree stem is lower in pH, lower in bases and nitrogen than the soil under leaf l i t t e r farther away from the stem, while in adjacent openings, without leaf l i t t e r , the soil is lower in exchangeable bases and nitrogen. Gersper et al_. (1967), Gersper (1970) and Gersper and Holowaychuk (1971), however, related the differences in pattern of fallout radionuclide distribution under single trees to the magnitude of the stemflow. Only throughfall distribution patterns were investigated in the present study, but the similarity of the results to the published work on soil properties indicates some important influence of throughfall on soils under the canopy of trees. A further explanation is therefore needed for the variability of nutrients on the forest floor. For any given rainstorm, the concen-tration of throughfall will be a function of the biomass of branches and foliage contacted by the descending water. The structure of the crowns of the trees used to obtain the data in Table 12, and Figures 11, 12 and 14 was such that the vertical column of crown biomass decreased towards the crown edge. However, redistribution of throughfall to stemflow and canopy-edge drip resulted in a very low throughfall volume at 0.5m (Table 12 and Figure 15) from the stem. The combination of the two patterns of volume and concentration resulted in the observed patterns of total throughfall chemistry. The low pH close to the stem indicates the higher acidity of the bark tissues of the larger branches. 73 5.5.4. Nutrient distribution on the forest floor. The return of nutrients from the aerial portions of trees to the forest floor in-fluences the chemical properties of s o i l s . The variability of chemical properties may be attributed to factors such as the throughfall quantity, throughfall chemical composition, and distribution patterns of crown washings and l i t t e r , as well as the rate of soil leaching. Tamm (1953, 1964) observed that the annual yield of Hylocomium as well as the nutrient concentration in the li v i n g moss vary inversely with light intensity under the tree canopy, and that outside the canopy, the moss yield de-creases regularly with distance until the moss is replaced by other species. It may be inferred from these findings that the growth of these mosses (and probably other ground flora) depends on the tree canopy and that the productivity of these plants is proportional to the amounts of nutrients released by the crown; In the present study, the radionuclide activities in the mosses growing under the inoculated trees followed the patterns of the nutrient input to the forest floor, so that mosses which were growing in areas receiving the greatest input of radionuclides contained greater radio-nuclide concentrations than those growing in areas receiving lesser inputs of radionuclides. It was therefore not possible in this study to differen-tiate the relative interception a b i l i t i e s of the different species of moss. Such comparisons could only be made by spraying the various species of mosses with equivalent amounts of radionuclides. We may suppose, however, that since mosses are said to depend on nutrients leached from the crown canopy (Tamm 1953, 1964), the observed Cs and Sr activities 74 of the mosses relative to the total isotope inputs indicate their nutrient requirements or their dependence on crown leachates. H_. splendens and L. menziesii which were growing close to the stems of the inoculated hemlock trees were found to exhibit high activities. TABLE 13 . pc 1 on Differential leaching of Sr and Cs in the forest floor (based on 8 single samples for each layer) 8 5 S r / 1 3 4 C s (data corrected to equal 1:1 8 5 S r and 134cs inoculation) Layers Soil core with moss Soil core without moss Moss .54 LF .86 1.20 H .55 1.97 Mineral soil (top 3 cm) 2 .23 3.63 5 . 5 . 5 . Differential leaching of Cs and Sr in the forest floor. 8 5 S r / 1 3 4 C s ratios in the forest floor components are presented in Table 13 . The increase of the ratios from the top layers to the 85 mineral soil layer indicates that Sr leaches more rapidly into the 1 ^ 4 deeper layers than Cs. This is similar to what was reported by Jordan ( 1 9 7 0 ) . CHAPTER 6 CONCLUSIONS The findings of this study (in relation to the main objectives) are that: 137 1. Cs fallout deposition in mosses is related to the mean annual 137 rainfall and that Cs concentration differs from species to species. Of the ground-dwelling mosses studied, Plagiothecium undulatum and Sphagnum squarrosum showed the highest activity levels. Since epiphytes are better interceptors of air-borne materials than ground-dwelling plants, i t is suggested that studies be made with epiphytic mosses (such as Neckera douglasii and Isothecium stoloniferum) to find the best indicator of 137 fallout materials. The activity of Cs in the mosses show that mosses can obtain nutrients from the air. 2. The amount of nutrients removed from the crown to the forest floor increases outwards from the stem to a peak value a short distance out from the stem and then drops steadily towards the crown edge. As a result, 134 ground-dwelling mosses close to the stem were found to have higher Cs 85 and Sr activities than at any other point beneath the crown. The mosses (eg. hL splendens and J^. menziesii) which were found to accumulate the 134 85 greatest quantities of Cs and Sr may be assumed to depend on crown leachates as their major source of nutrients. 75 76 3. Epiphytic mosses may obtain their nutrients from the stem tissues (of the host) or from the enriched rainwater from the overstorey crowns. It was found that about 70% of the nutrients from the overstorey canopy could be filtered by the epiphytic mosses and that these epiphytes showed 85 134 a preferential absorption of Sr over Cs. 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