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Carbon and nitrogen transformations in some forest floors Lacelle, Larry E. H. 1971

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CARBON AND NITROGEN TRANSFORMATIONS IN SOME FOREST FLOORS by Larry E. H. Lacelle B.S.F., The University of B r i t i s h Columbia, 1969 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department °f S o i l Science We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July, 1971 i i . In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it 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 Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of tS^Lyr A^X&visVsZ. The University of British Columbia Vancouver 8, Canada Date tf^ + T,? fr/. ABSTRACT An incubation technique was used to examine carbon mi n e r a l i z a t i o n and inorganic nitrogen accumulation i n samples of Douglas-fir and alder forest f l o o r s developed over s o i l s derived from g r a n i t i c , u l t r a b a s i c and limestone parent materials i n western B r i t i s h Columbia and Washington. Samples included L, F, and H or Hi horizons of Douglas-fir mor, raw moder, mu l l - l i k e moder and mull forest f l o o r s and alder t y p i c a l moder forest f l o o r s . Carbon dioxide production by the forest f l o o r materials provided an estimate of gross carbon mi n e r a l i z a t i o n and an approximate i n d i c a t i o n of gross nitrogen m i n e r a l i z a t i o n . Comparison of inorganic nitrogen accumulated and gross carbon mineralized indicated that a large f r a c t i o n of the mineralized inorganic nitrogen i s immobilized by the microbial population and (or) l o s t to d e n i t r i f i c a t i o n . The Hi horizons (organic horizons containing considerable incorporated mineral matter) accumulated more inorganic nitrogen than did the L and F horizons. Alder forest f l o o r s accumulated more inorganic nitrogen than did Douglas-fir forest f l o o r materials. Alder L horizons tended to accumulate ammonium nitrogen while the F and H i horizons accumulated n i t r a t e nitrogen. Douglas-fir mor forest f l o o r s were distinguished from t h e i r mull and moder counterparts by slower decomposition and less inorganic nitrogen accumulation, and by la r g e l y accumulating ammonium nitrogen i n a l l horizons. Irregular nitrogen accumulation curves, for some samples of Douglas-f i r L and F horizons were probably due to d e n i t r i f i c a t i o n losses. Incubation conditions favoring n i t r i f i c a t i o n , with no plant sinks to remove accumulated inorganic nitrogen, may have favored d e n i t r i f i c a t i o n losses. i v . ACKNOWLEDGEMENTS This study was made possible by grants from the University of B r i t i s h Columbia and the National Research Council. Special acknow-ledgement i s offered to Dr. T. M. Ba l l a r d for suggesting the nature of the research and for h i s assistance and advice. The author also wishes to thank Dr. C. A. Rowles and Dr. J . P. Kimmins for t h e i r advice and c r i t i c a l review of the manuscript. V . TABLE OF CONTENTS INTRODUCTION LITERATURE REVIEW STUDY OBJECTIVES LOCATION AND DESCRIPTION OF SITES MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS LITERATURE CITED APPENDIX I: Cumulative carbon mineralized APPENDIX I I : Rate of carbon mineralization APPENDIX I I I : Nitrate nitrogen accumulated APPENDIX IV. Ammonium nitrogen accumulated APPENDIX V: Inorganic nitrogen accumulated APPENDIX VI: Outline of the c l a s s i f i c a t i o n used characterizing horizons and forest Page I 2 4, •5 10 13-39 41 43 46 49; 52 55 in 58 floors v i . TABLES Table Page 1 Location and description of si t e s 7 2 Elemental composition of the forest floor materials 14 3 Summary of results of analysis of variance and Duncan's 17 New Multiple Range Test applied to the three-week means of carbon mineralized and inorganic nitrogen accumulated for tree species, forest floor types, horizons and parent materials 4 Mean values for carbon mineralized and inorganic 22 nitrogen accumulated for horizons and tree species 5 Summary of carbon mineralized and n i t r a t e , ammonium 24 and inorganic nitrogen accumulated for a l l samples 6 Summary of results of analysis of variance and Duncan's 30 New Multiple Range Test applied to the three-week means of ni t r a t e nitrogen, ammonium nitrogen and inorganic nitrogen accumulated for a l l Douglas-fir samples 7 Summary of results of analysis of variance and Duncan's 32 New Multiple Range Test applied to the three-week means of rate of carbon mineralization for a l l samples 8 Summary of correlation coefficients r e l a t i n g C/N ratios 35 and pH to carbon mineralized and inorganic nitrogen accumulated for a l l samples FIGURES v i i . Figure 1 Site locations 2 Carbon mineralized and inorganic nitrogen accumulated for Douglas-fir samples, s i t e number 8 Page 6 18 Carbon mineralized and inorganic nitrogen accumulated for alder samples, s i t e number 13 Carbon mineralized and inorganic nitrogen accumulated for mor, moder and mull forest floors Inorganic nitrogen, n i t r a t e nitrogen and ammonium nitrogen accumulated for alder samples, s i t e number 15 19 20 27 Inorganic nitrogen, nitr a t e nitrogen and ammonium nitrogen accumulated for Douglas-fir samples, s i t e number 3 28 Rate of carbon mineralization for Douglas-fir samples, s i t e number 8, and alder samples, s i t e number 14 31 10 Inorganic nitrogen accumulated for Douglas-fir samples, s i t e number 5 Carbon mineralized, plotted against pH for a l l samples Inorganic nitrogen accumulated, plotted against C/N r a t i o for a l l samples 33 36 37 1. INTRODUCTION In many of the forested areas of the world nitrogen deficiencies are a common tree n u t r i t i o n a l problem. As a f i r s t step i n solving such problems, the pathways, rates and quantities of organic and mineral nitrogen accumulation must be understood. Because a large proportion of the inroganic nitrogen content of forest floor materials i s often immobilized, i t i s d i f f i c u l t to gain an estimate of gross nitrogen mineralized. However, this can be achieved i n d i r e c t l y by using the quantity of carbon mineralized over a given period of time as an indicator of gross nitrogen mineralization. Carbon mineralization is r e l a t i v e l y easy to measure and as organic carbon makes up a r e l a t i v e l y large portion of the forest floor material (30-507,) i t s mineralization gives a s a t i s -factory representation of gross organic matter decomposition. Two common methods of analyzing the rates and patterns of carbon and nitrogen mineralization are: analysis of changes under natural f i e l d conditions using periodic destructive sampling or lysimetry, and laboratory incubation of s o i l samples. The former method, while y i e l d i n g results more comparable to those found in nature, has the disadvantages of high cost and d i f f i c u l t y of standardizing experimental conditions. Incubation results represent mineralization under a r t i f i c i a l conditions, but i n spite of this are valuable as indicators of a s o i l ' s mineralization potential. Reviews of incubation technique and application of incubation results to a g r i c u l t u r a l situations are contained i n a r t i c l e s by Harmsen and Van Schreven (1955) and Bremner (I960). Attempts to apply incubation techniques to forest floor material have met with varying success as the forest floor materials are variable in state of decomposition, and being partly humified, are often resistant to decomposition. Therefore, long incubations are required. In addition, in forestry work the r e l a t i v e importance of the various forest floor horizons must be assessed as these organic horizons vary i n rate of decomposition. In view of these considerations, the incubation technique used in this study involved three-month incubations of L, F and H or Hi horizon materials coupled with periodic analysis for carbon and n i t r o -gen transformations. (Distinction of horizons i s outlined in Appendix VI). LITERATURE REVIEW Few studies dealing with rates and quantities of carbon and nitrogen mineralized i n forest floors are available. In Germany, ZtJttl (1960) has studied rates of carbon dioxide production as an indicator of gross nitrogen mineralization for duff mull, mull and mor forest f l o o r s . In incubation studies he found no correlation between C/N r a t i o and accumulation of mineral nitrogen for different forest floor types. He attributed this to differences i n decomposability. However, for mor and duff mull forest floors he found a positive correlation;; between i n i t i a l nitrogen content and accumulation of mineral nitrogen. For a Scots pine mor forest f l o o r , Zb'ttl observed that both C0 2 production and mineral nitrogen accumulation were greatest in the L horizons, lower in the F and least i n the H horizons. Results for a Norway spruce stand were si m i l a r . In Norway, Mork (1939) studied the effects of water content and incubation temperature on CO2 production and mineral nitrogen accumulation for three types of forest floor material. He showed that 40 to 55 volume percent of water represented optimum moisture conditions for n i t r i f i c a t i o n and that ammonium nitrogen could accumulate at water contents as high as 3. 75 volume percent. For mor forest floor material, 20°C represented the optimum temperature for n i t r a t e nitrogen accumulation. He found that when temperature was increased over the range of 10 to 30°C, production was more rapid i n i t i a l l y , but less rapid subsequently. At high water contents, such as 75 volume percent, production was inhibited. In general, Mork found that, for the range of temperatures and water contents studied, nitrogen mineralization was less affected by water content than by temperature. He recommended use of a 20°C temperature and 55 volume percent water content (about 2/3 of f u l l saturation) as standard conditions to be used i n incubation studies of forest floor materials. Cole (1963) and B a l c i (1963) used lysimetry to study quantities of several elements leached from different Washington forest floors and s o i l s . B a l c i showed that for alder forest floors approximately 0.74% of the t o t a l nitrogen was released over an eight month period. S i m i l a r l y , for Douglas-fir, Cole observed release of 1.8 to 2.2% df the t o t a l forest floor nitrogen over one year. In an incubation test with F and A-Q horizon material from a Douglas-f i r , hemlock and Sitka spruce stand, Bollen et a l . (1963) determined the amounts of t o t a l nitrogen mineralized to n i t r i t e , nitrate and ammonium nitrogen. The conifer F horizons had greater accumulations of both n i t r a t e and ammonium nitrogen (0.8% and 0.9% of the t o t a l nitrogen) but in the A-Q horizon the conifers accumulated less n i t r a t e nitrogen (0.5%). Alder F horizons accumulated s l i g h t l y less n i t r a t e and ammonium nitrogen (0.3 and 0.8%) than did conifer F horizons but alder A-Q horizons had much greater accumulations of ni t r a t e and ammonium nitrogen (1.4 and 2.2% of the t o t a l nitrogen). STUDY OBJECTIVES The main objective of th i s study was to examine carbon and nitrogen m i n e r a l i z a t i o n i n the many types and horizons of Douglas-fir and alder forest f l o o r materials. In add i t i o n , i t was desired to evaluate the r e l a t i v e e f f e c t s of limestone, u l t r a b a s i c and g r a n i t i c parent materials on min e r a l i z a t i o n . D i f f e r e n t forest f l o o r types and t h e i r respective horizons were studied i n order to evaluate differences i n quantities of min e r a l i -zation that might be rel a t e d to morphological features of forest f l o o r s . M i n e r a l i z a t i o n i n Douglas-fir forest f l o o r material was studied because inorganic nitrogen d e f i c i e n c i e s are a common tree n u t r i t i o n a l problem for t h i s species; Alder forest f l o o r material was studied i n order to compare the r e l a t i v e quantities of inorganic nitrogen accumulated under this symbiotic nitrogen f i x e r with quantities accumulated under Douglas-fir. G r a n i t i c , u l t r a b a s i c and limestone parent materials were examined i n order to evaluate the e f f e c t s of these materials on fo r e s t f l o o r c h a r a c t e r i s t i c s and on rates and quantities of min e r a l i z a t i o n . The rates and quantities of carbon mineralized were measured i n order to estimate the decomposability of the various forest f l o o r horizons and to estimate gross nitrogen m i n e r a l i z a t i o n . Patterns and quantities of i n -organic nitrogen accumulated as n i t r a t e and ammonium nitrogen were examined i n order to evaluate the r e l a t i v e quantities of each nitrogen form accumulated i n the L, F and H or Hi horizons of the d i f f e r e n t forest f l o o r types. LOCATION AND DESCRIPTION OF SITES Douglas-fir and alder stands were sampled in western B r i t i s h Columbia and Washington (Figure 1) on g r a n i t i c , u l t r a b a s i c and limestone parent materials. Samples were c o l l e c t e d from as great a v a r i e t y of s i t e s as possible i n order to study carbon and nitrogen m i n e r a l i z a t i o n under a range of conditions. Mor, moder (duff mull) and mull forest f l o o r s (Appendix VI) were sampled by horizon for each tree species and each parent, material (Table 1). Table 1. Location and description of sites Site and Location Elevation Forest Floor Horizon Nature of S o i l Tree Species and Horizon f t Description Thickness Parent Material Approx. Age cm and Bedrock Mors 1 Lj F H 2 L F •H Hollyburn 2,000 Mtn., B.C. Twin Sisters 3,400 Mtn., Wash. thick granular mor thick granular mor .2 6.1 10.2 .4 6.9 6.4 sandy g l a c i a l t i l l over g r a n i t i c rock ultrabasic rock outcrop WH, WRC, PSF,* 200 yrs. DF, WH, WRC 294 yrs. Raw Moders 3 L F Hi 4 L F Hi Coquitlam 650 Watershed, B.C. Fulford 100 Harbor, B.C. raw moder raw moder i.l 3.1 1.3 .4 1.9 1.3 sandy loam, g l a c i o - f l u v i a l deposits over g r a n i t i c rock g r a n i t i c rock outcrop DF, WH, wr.c, 70 yrs. Df, a, go, 86 yrs. 5 L F Hi Boston Bar B.C. 2,500 raw moder .2 3.5 3.2 ultrabasic talus DF, 420 yrs. slope 6 L F Hi Texada Island, 600 B.C. calcareous raw moder .2 5.7 6.4 limestone rock DF, WRC, outcrop 96 yrs. Table 1 continued. Location and description of sites Site and Location Elevation Horizon f t Forest Floor Description Horizon Thickness cm Nature of S o i l Parent Material and Bedrock Tree Species and Approx. Age 7 L.-: F Hi 19 Mile Creek, B.C. 3,000 calcareous raw moder .2 4.9 1.9 limestone rock outcrop DF, wrc, * 465 yrs. 8 L F Hi Limestone Junction, Wash. 1,800 calcareous raw moder .3 3.2 3.2 sandy loam over limestone rock DF, GF, bm, be, 60 yrs. Mul l - l i k e Moders and Mulls 9 L F Seymour River, 1,000 B.C. mul1-1ike moder .1 2.5 sandy alluvium DF, ra , wh, over g r a n i t i c rk. psf, ss, 348 yrs. 10 L F Twin Sisters 2,300 Mtn., Wash. mul1-1 ike moder .1 .6 sandy loam over ultrabasic rock DF, WRC, 56 yrs. 11 L F Quadra Island, B.C. 200 mul1-1ike moder 7.6 limestone rock outcrop DF, WRC, wh, 56 yrs. 12 L • V F Cathedral Grove, B.C. 900 coarse mull .2 4.1 s i l t y clay loam over ba s a l t i c rock DF, WRC, wh, 600 yrs. 13 L F Hi Capilano Lake, B.C. 650 Typical Moders typical moder .1 1.9 1.3 sandy loam, g l a c i o - f l u v i a l deposits over gr a n i t i c rock RA, 30 yrs, oo Table 1 continued. Location and description of sites Site and Location Elevation Forest Floor Horizon Nature of S o i l Tree Species and Horizon f t Description Thickness Parent Material Approx. Age cm and Bedrock 14 L Twin Sisters 2,000 typical moder .1 sandy loam RA,* 25 yrs. F Mtn., Wash. 1.9 over ultrabasic Hi 1.3 rock 15 L Popkum, B.C. 500 typ i c a l moder .1 loam over RA, bm, be, F .9 limestone rock 25 yrs. Hi 5.4 * DF - Douglas-fir, WRC - western red cedar, WH - western hemlock, GF - grand f i r , PSF - P a c i f i c s i l v e r f i r , SS - Sitka spruce, A - arbutus, BC - b i t t e r cherry, GO - Garry oak, BM - bigleaf maple, RA - red alder. Small l e t t e r s designate minor stand components. MATERIALS AND METHODS On each s i t e F and H horizons were sampled at the four corners of a 12 m square. Because of i t s r e l a t i v e scarcity (Table 1) fresh L horizon material was collected at as many points as required i n order to obtain s u f f i c i e n t sample for incubation and analysis. In order to disrupt the normal mineralization processes as l i t t l e as possible, samples were collected, composited, transported and stored in the minimum amount of time possible. Replicate horizon samples were composited and stored i n a i r - t i g h t p l a s t i c bags i n a portable cooler u n t i l transported to the laboratory for r e f r i g e r a t i o n at 3°C. Samples were roughly sorted through a 0.6 cm screen in order to remove wood, roots and other large debris. Alder L and F material was chopped in a Waring commerical blender i n order to reduce i t to a size able to pass through the screen. In the laboratory, forest floor samples were placed i n cylinders with wire screen bases and wetted u n t i l a free water f i l m was evident at the sample surface. The water content of this sample, after overnight drainage with r e s t r i c t e d evaporation, was assumed to represent the maximum water holding capacity. Samples to be incubated were adjusted to 60% of t h i s water content. For each horizon, two 10-g (oven dry weight equivalent) samples for C O 2 analysis and two 15-g (oven dry weight equivalent) samples for nitrogen analysis were placed i n a Percival growth chamber (Model PGC-78) and incubated at 18°C and 98 to 99% r e l a t i v e humidity for 12 weeks. The high humidity was maintained by using 2 or 3 Sovereign humidifiers (model 707) adjusted to operate continuously. Water contents were checked per i o d i c a l l y and samples were rewetted with d i s t i l l e d water i f they showed evidence of drying. The 18°C temperature used i n th i s study approximates mean summer temperature near the surface of the mineral s o i l for coastal B r i t i s h Columbia better than do the commonly used incubation temperatures of 20 to 35°C (Brook, 1965; McMinn, 1957). For CO2 analysis, measurements were made using a Beckman Infrared Analyzer (model 215A). A i r of known CQ2 content was passed over the samples at a constant flow rate and when a steady state had been attained the output CO2 concentration was measured. Samples were maintained at 18°C during C 0 2 analysis by immersion i n a water bath. The rate of C 0 2 production was measured da i l y at f i r s t , then less frequently as the rate of carbon mineralization approached a steady state. Mass of carbon mineralized was calculated from volumetric CO2 concentration using the conversion 0.5 g carbon equals 1 l i t r e CO2 at c a l i b r a t i o n and analysis conditions of 22°C and 1 atmosphere. Five g (wet weight) of each sample being incubated for nitrogen analysis was removed every three weeks and analyzed for nitra t e and ammonium nitrogen by extracting the inorganic nitrogen with a 1% KAl(SO^) solution. This extract was used i n the ammonium nitrogen determination using a micro-difusion technique, Nesslerization and colorimetry at 431 ration, a Bausch and Lomb Spectronic 20 spectrophotometer. Quantities of nitra t e nitrogen were evaluated using a xylenol-colorimetric technique These two methods of inorganic nitrogen analysis are. described by Zb"ttl (1960) and were selected as they proved to be r e l i a b l e i n detection of the small amounts of inorganic nitrogen generally present i n forest floor material. Analysis was not made for n i t r i t e nitrogen, as for P a c i f i c Northwest conditions quantities of this nitrogen from are generally much smaller than amounts of ammonium and nit r a t e nitrogen (Bollen et a l . , 1963). Considering the scope of th i s project and the amount of time available for analysis, i t was not considered p r a c t i c a l to evaluate losses due to d e n i t r i f i c a t i o n during incubation. Total nitrogen was estimated by using a standard micro-Kjeldahl technique (Black, 1965). A Caro's acid digest was prepared for the determination of K, P, Mg and Ca (Lindner and Harley, 1942) the quantities of these elements being determined using a Perkin-Elmer Atomic Adsorption Spectrophotometer (Model 303). Total phosphorus was determined using a wet ashing technique and analysis by the vanadomolybdophosphoric yellow color test (Jackson, 1958). Total carbon was determined by volumetric CO2 analysis after oxidation of a 0.1-g sample with iron and t i n acceler-ators in a Leco Induction furnace (Model 507-100). A l l pH measurements were made on an Instrument Laboratories Portomatic pH Meter using a glass electrode and a 7/1 r a t i o of water to forest floor material. In the following sections, quantities of carbon mineralized are expressed as percentages of i n i t i a l t o t a l carbon. Rates of carbon minera-l i z a t i o n are expressed as a percentage of the i n i t i a l t o t a l carbon mineralized in one day. Quantities of nitrate nitrogen, ammonium nitrogen and inorganic nitrogen (the sum of ammonium and ni t r a t e nitrogen) accumulated are expressed in terms of percentages of i n i t i a l t o t a l nitrogen. RESULTS AND DISCUSSION Concentrations of N, P, K, Mg, Ca and C i n a l l samples tested are given i n Table 2. High concentrations of Ca are evident in samples from limestone areas. However, high Mg concentrations are not evident i n samples c o l l e c t e d i n areas of u l t r a b a s i c parent materials. In most forest f l o o r samples Mg concentration increases with depth while K concentration decreases with depth. Carbon concentration generally decreases i n the order L, F and H or Hi horizons, while t o t a l nitrogen concentration i s generally highest i n the F, followed by the H or Hi and the L horizons. Alder L horizons are an exception, often having a higher concentration of t o t a l nitrogen than the F or Hi. When alder t y p i c a l moders are compared with Douglas-fir mors, raw moders and mulls i t appears that alder Hi horizons are r e l a t i v e l y d e f i c i e n t i n Ca unless the parent material is limestone.- Alder L and F horizons generally appear to have greater concentrations of K and N than do corres-ponding Douglas-fir horizons. Due to the high nitrogen content of alder l i t t e r , the c/N r a t i o i n alder forest f l o o r material does not s i g n i f i c a n t l y decrease with depth as i t does in Douglas-fir L, F and H or Hi horizons. Forest f l o o r s from limestone and u l t r a b a s i c areas generally are less a c i d than forest f l o o r samples from g r a n i t i c areas. However, there are many exceptions, due to the fact that pH was measured i n highly organic forest f l o o r materials that do not necessarily r e f l e c t the a c i d i t y of the mineral s o i l or parent material. Total percentages of carbon mineralized and inorganic nitrogen accumulated for each sample were grouped according to tree species, horizon, forest f l o o r type or parent material type. The means of percen-tages of carbon mineralized and inorganic nitrogen accumulated were used Table 2. Elemental composition of the forest floor materials Site and % C/N Horizon N P K Mg Ca C Ratio PH Mors 1 L 1.051 .104 Trace .033 .551 49.91 47.49 4.12 F 1.571 .124 I I .043 .141 48.64 30.96 3.79 H 1.608 .104 .006 .040 .210 49.64 30.87 3.89 2 L .919 .064 .059 .042 .531 50.07 54.48 4.25 F 1.479 .124 .043 .056 .176 50.17 33.94 4.38 H 1.462 .111 .029 .060 .140 48.73 33.33 3.80 Raw Moders 3 L 1.125 .064 .019 .049 .571 49.09 43.63 6.52 F 1.656 .124 .017 .081 .150 45.45 27.45 4.42 Hi 1.660 .124 Trace .154 .042 35.09 21.14 4.29 4 L 1.104 .215 .586 .155 .811 49.58 44.91 3.98 F 1.579 .155 .106 .157 .546 45.80 29.01 5.12 Hi 1.303 .226 .086 .316 .055 20.73 15.91 5.63 5 L .901 .173 .307 .116 .812 48.11' 53.40 4.28 F 1.539 .165 .084 .278 .892 42.06 27133 5.42 Hi 1.242 .192 .084 .559 .606 29.88 24.06 5.97 6 L 1.348 .215 .258 .103 1.463. 48.39 35.90 4.27 F 1.393 .143 .025 .121 3:257| 39.29 28.20 7.92 Hi 1.368 .135 .021 .138 3;:537# 37.25 27.23 7.72 7 L .885 .184 .289 .070 1.263 . 50.09 56.60 4.29 F 1.340] .111 .062 .135 1.523 44.77 33.41 5.52 Hi 1.315 .135 .098 .456 1.463 33.54 25.51 3.93 continued. Table 2 continued. Elemental composition of the forest floor materials Site and Horizon % C/N i Ratio PH N P K Mg Ca C 8 L 1.291 .226 .360 .133 1.082 ' 49.25 38.15 4.22 F . 1.689 .135 .064 .166 1.693 43.12 25.53 6.38 Hi 1.376 .143 .039 .211 1.453 31.27 22.72 6.53 Mul l - l i k e Moders and Mulls 9 L 1.392 .093 .186 .100 .852 50.15 36.03 5.07 F 1.717 .124 .089 .240 .416 42.49 24.75 5.12 10 L 1.189 .123 .078 .166 .832 45.50 38,27 4.99 F 1.254- .124 ,037 .330 ,235 37.22 29.68 5.22 11 L .719 .104 .041 .057 1.052 49.54 68.90 4.68 F 1.413 .143 .066 .178 1.223 47.09 33.33 6.16 12 L 1.185 .124 .215 .129 .761 49.30 41.60 4.72 F 1.153 .165 .053 .428 .156 41.31 35.83 4.74 Typ i c a l Moders 13 L 3.329 .124 1.134 .165 .851 47.99 14.42 5.79 F 2.615 .124 .064 .141 .591 48.51 18.55 4.32 Hi 1.831 .155 .031 .313 .090 27.59 15.07 4.22 14 L 3.179 .135 .606 .371 .702 48.97 15.40 4.80 F 2.899 .124 .051 .177 .451 47.61 16.42 4.23 Hi 2.645 .111 Trace .377 .065 40.60 15.35 6.42 15 L 2.136 .104 1.349 .148 1.423 47.80 22.38 5.73 F 2.485 .135 .203 .155 .431 43.94 17.68 5.58 Hi 1.559 . .192 .072 .421 .702 18.52 11.88 5.29 i n the analysis of variance and Duncan's New Multiple Range Test i n order to detect s i g n i f i c a n t differences. Results are shown i n Table 3 and indicate that percentages of i n i t i a l t o t a l carbon mineralized and percentage of inorganic nitrogen accumulated were s i g n i f i c a n t l y greater for alder than for Douglas-fir forest floors (Table 5; Figures 2 & 3). This i s probably a r e f l e c t i o n of the greater decomposability of fresh alder debris and the high nutrient status of alder forest floor materials (Table 2). With abundant t o t a l nitrogen, as i n alder forest floor materials immobilization i s less than i n Douglas-fir forest floors and more inorganic nitrogen can accumulate as a by-product of microbial a c t i v i t y . In the analysis of variance test comparing horizons, the L horizons had s i g n i f i c a n t l y greater mineralization of carbon than did the F and H or Hi horizons (Table 3; Figure 4). The L horizons have a greater concen-t r a t i o n of readily decomposable organic matter compared to the F and H or Hi horizons, where such materials have been largely lost through minera-l i z a t i o n . Percentages of carbon mineralized i n the F horizons were generally greater than i n H or Hi horizons but the difference, on the average, was not s t a t i s t i c a l l y s i g n i f i c a n t (Table 3). In a few cases, mineralization rates were more rapid i n the Hi horizons (see Appendix I ) . An example is s i t e number 4 from the Gulf Islands. This s i t e had an extensive understory vegetative cover with large quantities of l i v e root material in the H i , th i s fresh material being readily mineralized. Although percentages of carbon mineralized i n alder L horizons were much greater than i n Douglas-fir L horizons (Table 4) the proportion of carbon mineralized i n the F and Hi horizons was not appreciably greater for alder than for Douglas-fir. Thus, i t appears that the alder L horizons Table 3. Summary of results of analysis of variance and Duncan's New Multiple Range Test applied to the three-week means of carbon mineralized.(percentage of i n i t i a l t o t a l C) and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) for tree species, forest floor types, horizons and parent materials Nitrogen Carbon alder 8.04 Douglas-fir 1.65 alder 29.23 Douglas-fir 18.59 Typical Moder 8.04 Raw Moder • 1.82 Mull .147 Mor 1.38* Typical Moder 29.23 Mull 21.42 Raw Moder 18.97 Mor 9.22 H & Hi F L L F H & Hi 6.11 2.31 1.16 28.74 16.01 14.01 gra n i t i c ultrabasic limestone limestone g r a n i t i c ultrabasic 4.46 2.48 2.48 24.25 19.96 17.27 * Means underlined by the same li n e did not d i f f e r s i g n i f i c a n t l y according to Duncan's New Multiple Range'Test at the 5% l e v e l . OP c ro CARBON MINERALIZED (PERCENTAGE OF INITIAL TOTAL C) Hi O O S3 M H c r a o 0 p era g P p CO (D 1 H Hi S3 H- I- 1 l-f p. N CO tD fu 3 13 t —1 ro co S3 P a p CD O H- H rr 09 ro fu P s ; H-o o p OO H-rf i-i O 09 ro p S3 o o p I ro a. m m o -n INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) o <o c CD > —I — — ro o ro o -i o CD m v s •8T OP c ri ro CARBON MINERALIZED (PERCENTAGE OF INITIAL TOTAL C) ft) rf, O O ft) H i-i cr o ' 1 P CL ro g i-i H-0 CD ft) pi I-i g £u x> I—' ' 1 H-rt> N cn fD » Ch cn ft) H- P rt CL ro 3 0 o o • l-t OQ 1—' ft) U> 0 o 0 H-n-H o OQ ro 0 a> o o 1 ro a. 3 m m IK. CO z o c CD INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) 3 m m CA o o c CD > ro o T O ~r 20 o o m '61 CARBON MINERALIZED (PERCENTAGE OF INITIAL TOTAL C) MORS RAW MODERS MULL-LIKE MODERS AND MULLS TYPICAL MODERS MORS RAW MODERS MULL-LIKE MODERS AND! MULLS TYPICAL MODERS MORS RAW MODERS TYPICAL MODERS INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) 21. contain more readily decomposable material than does the Douglas-fir l i t t e r , but once this is mineralized, the alder F and Hi horizons are almost as resistant to mineralization as are the corresponding Douglas-f i r horizons. Patterns observed for carbon mineralization do not apply to net nitrogen accumulation, as the concentrations of inorganic nitrogen are s i g n i f i c a n t l y greater i n the H and Hi horizons than i n the F and L horizons (Tables 3 & 4; Figures 2 & 3). The mean percentage of nitrogen accumulated in inorganic forms in the H and Hi horizons i s 81 and 62% greater than the corresponding values for the L and F horizons, respectively, the mean value for accumulated inorganic nitrogen i n F horizons i s greater than the comparable value for L horizons but the difference i s not s i g n i -f i c a n t . The greater inorganic nitrogen accumulations i n the H or Hi horizons probably re s u l t from the tendency for less nitrogen immobiliza-t i o n to occur in the more decomposed organic matter and from leaching of the products of mineralization into the lower horizons. The Hi horizons appear to represent an optimum combination of n u t r i t i o n and environment for microbial a c t i v i t y and subsequent release of inorganic nitrogen. I t i s interesting to note that for alder sit e s 13 and 14, the percentage of inorganic nitrogen accumulated in the Hi is similar to the percentage of t o t a l carbon mineralized (Figure 3). Generally, quantities of carbon mineralized are much greater than quantities of inorganic nitrogen accumulated (Figure 4). In samples 13 and 14, where gross carbon mineralization and net nitrogen accumulation are s i m i l a r , inorganic nitrogen immobilization must be r e l a t i v e l y small, and conditions optimum for inorganic nitrogen accumulation. Table 4. Mean values for carbon mineralized (percentage of i n i t i a l t o t a l C) and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) for horizons and tree species Horizon L F H or Hi Element N C . :N % C N C Douglas-fir .36 23.21 1.52 15.62 3.80 13.72 alder 4.36 50.80 5.46 17.53 14.29 19.39 both 1.16 28.74 2.31 16.01 6.11 14.01 In alder t y p i c a l moders, ammonium nitrogen accumulation is common in the L horizons while the F and Hi horizons tend to accumulate a greater proportion of nitrate nitrogen (Table 5; Figure 5; Appendices I I I and IV). Douglas-fir mors accumulate mostly ammonium nitrogen (Table 5) while raw moders accumulate both nitra t e and ammonium nitrogen i n the F and L horizons with a greater proportion of ammonium nitrogen i n the Hi horizons (Table 5; Figure 6). In a comparison of forest floor types i t was found that alder t y p i c a l moders and Douglas-fir mulls had s i g n i f i c a n t l y greater carbon mineralization than did Douglas-fir raw moders and mors (Table 3; Figures 2, 3 & 4). Alder t y p i c a l moders and Douglas-fir mulls and raw moders had s i g n i f i c a n t l y greater carbon mineralization than did mor forest f l o o r s . With regards to r e l a t i v e inorganic nitrogen accumulation, t y p i c a l moders had s i g n i f i c a n t l y greater accumulations than did raw moders, mulls or mors (table 3). Lower inorganic nitrogen accumulation i n mors is attributed to the advanced stage of humification and to less microbial a c t i v i t y . As mentioned previously, mors had less n i t r i f i c a t i o n than the other types of forest floor and as a r e s u l t , accumulated ammonium nitrogen, especially i n the H horizon (Table 5; Appendices I I I and IV). In the analysis of variance and Duncan's New Multiple Range Test applied to the tree types of parent materials, the three week means of quantities of carbon mineralized and inorganic nitrogen accumulated did not dif f e r V s i g n i f i c a n t l y with parent material type (Table 3). However, effects of parent materials were apparent i n the higher n i t r i f i c a t i o n evident i n horizon samples collected from site s 6, 7, 8, 11 and 15, areas of limestone parent materials (Table 5; Figure 5). Table 5. Summary of carbon mineralized (percentage.of i n i t i a l t o t a l C) and ni t r a t e , ammonium and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) for a l l samples after 12 weeks of incubation Site and Carbon Nitrate Ammonium Inorganic kg/ha Horizon Mineralized Nitrogen. Nitrogen Nitrogen Inorganic Accumulated Accumulated Accumulated Nitrogen 1 Accumulated Mors 1 L 18.7 .5 .2 .7 .19 F 8.6 .2 3.5 3.7 45.83 H 4.3 .1 2.1 2.2 48.40 2 L 17.8 0 .1 .1 .04 F 7.1 0 .1 .1 1.97 H 6.8 .2 1.3 1.5 18.96 Raw Moders 3 L 12.2 .1 .1 .2 .02 F 10.4 .1 1.6 1.7 11.65 Hi 8.6 2.8 3.4 6.2 17.41 4 L 25.8 .2 0 .2 .10 F 17.4 .2 .4 .6 2.05 Hi 26.5 3.7 6.6 10.3 22.63 5 L 25.5 .4 .2 .6 .12 F 14.6 .2 .1 .3 1.91 Hi 16.4 1.9 1.0 2.9 15.06 6 L 26.2 .2 .1 .3 .09 F 17.3 1.3 .2 1.5 16.01 Hi 15.2 .1 .3 .4 4.75 continued. Table 5 continued. Summary of carbon mineralized (percentage of i n i t i a l t o t a l C) and n i t r a t e , ammonium and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) for a l l samples after 12 weeks of incubation Site and Carbon Nitrate Ammonium Inorganic Kg/ha Horizon Mineralized Nitrogen Nitrogen Nitrogen Inorganic Accumulated Accumulated Accumulated Nitrogen Accumulated 7 L 20.3 .1 . 1 . 2 .06 F 15.2 0 .1 .1 .51 Hi 16.2 1.3 .2 1.5 4.89 8 L 35.9 .1 .1 .2 .09 F 21.9 .2 0 .2 1.45 Hi 15.9 5.3 .1 5.4 30.95 Mu l l - l i k e Moders and Mulls 9 L 16.5 0 0 0 0 F 19.8 3.7 .2 3.9 21.81 10 L 16.3 .1 0 .1 .02 F 18.4 0 0 0 0 11 L 23.5 .9 .2 1.1 .29 F 17.8 .3 .3 .6 8.79 12 L 40.1 .4 .2 .6 .17 F 19.0 .3 .3 .6 3.47 Raw Moders 13 L 49.2 .2 5.3 5.5 2.38 F 17.2 5.5 .2 5.7 3,7.25 Hi 15.6 13.9 2% 16.3 50.36 continued. Table 5 continued. Summary of carbon mineralized (percentage of i n i t i a l t o t a l C) and n i t r a t e , ammonium and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) for a l l samples after 12 weeks of incubation Site and Horizon Carbon Mineralized Nitrate Nitrogen Accumulated Ammonium Nitrogen Accumulated Inorganic Nitrogen Accumulated kg/ha Inorganic Nitrogen Accumulated 14 L 49.7 .3 F 10.5 5.4 Hi 6.8 6.5 15 L 53.4 .1 F 24.9 4.6 Hi 35.8 18.1 7.1 7.4 '3;05 .6 6.0 29.29 1.8 8.3 37.40 .1 .2 .06 .1 4.7 13.77 .2 18.3 200.84 OQ c H fD CU H O P O O C H g OP t-1 P CO H-rt O fD Cu p H' hh rt O i-J i-i O OQ Co fD i - P Cu -fD P CO 3 1 — ' fD CD co i-i r 1- o rt OP fD fD P 3 O Co • P . Cu Ln Co O P P H-rt H O OP fD P 3 m m z o c CD > H O m o c CD > INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) oo ro ro o OJ F7 T T 0> R CO ro H o O CD CD > rn z 2 o \ \ \ r"n\ NITRATE NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) GO — — ro OJ a> T JN2_ 0> T Z Z —i H O > CD H m m AMMONIUM NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) oo 3E m m CO o o c CD > OJ H-0> to h T r 5 _ ro X z > M o o CD Z m c OP H fD ft) H .O p D O g OQ C IB ft) H-rt o fD O. 3 i - h rt O i-i i-i O OQ O fD 0 3 C -OQ i -1 3 ft) H-co r+ 1 i-i Hi ft) H- rt >-i fD co 3 ft) H> g rt 1—1 O fD OQ CD fD <• 3 CO ft) H- 3 rt a. fD ft) o g • o 3 CO H-§ 3 H-rt i-i O OQ fD 3 m m CO o c CD m m CO o c CD > H O Z m m CO o o c 00 > H O z INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) ro CM O - Ll ro -Pi T H O o o o > m z NITRATE NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) o ro ^ OJ cn T T z z H —1 TO O > CD —1 m m z ro AMMONIUM NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) O ro * CM c n ID ro i i i i * \ \ \ T \ z > H i si 51 82 Quantities of carbon mineralized are generally much greater than quantities of inorganic nitrogen accumulated, especially in the L horizons (Table 5; Figures 2, 3 & 4; Appendices I & V). This suggests that during decomposition large quantities of inorganic nitrogen are immobilized by the microbial population. Many samples indicate immobilization i n that inorganic nitrogen content declines i n the f i r s t s three weeks of incubation (Appendix V; Figures 5 & 6). However, comparison of the three-week means of inorganic nitrogen accumulated for a l l samples by analysis of variance and Duncan's New Multiple Range Test shows that on the whole, the differences between weeks 0 and 3 are not s i g n i f i c a n t (Table 6). Figure'. 7 i l l u s t r a t e s rates of carbon mineralization and depicts a high i n i t i a l rate followed by a long period of reasonably constant mineralization when microbial populations have presumably s t a b i l i z e d somewhat after adjusting to incubation conditions. Application of analysis of variance and Duncan's New Multiple Range Test to the three-week means of rates of carbon mineralization showed that the rate of carbon mineralization i n weeks 0 and 3 was s i g n i f i c a n t l y greater than the rate i n weeks 6 to 12 (Table 7). S t a b i l i t y of the microbial populations i s implied by the fact that the rate of carbon mineralization did not vary s i g n i f i c a n t l y during the last 6 weeks of the test. In some forest floor samples (especially Douglas-fir L and F horizons) inorganic nitrogen accumulation decreased during the l a t t e r part of the incubation test (Figure 8; Appendix 5). However, on the average, the three-week means for each of n i t r a t e , ammonium and inorganic nitrogen accumulated did not vary s i g n i f i c a n t l y during the la s t 6 weeks of the test (Table 6). Douglas-fir H and Hi horizons and generally a l l alder Table 6. Summary of results of analysis of variance and Duncan's New Multiple Range Test applied to the three-week means of nitrate nitrogen, ammonium nitrogen and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) for a l l Douglas-fir samples weeks means weeks means weeks means Nitrate Nitrogen 12 9 6 0 3 .778 .706 .250 .222 .181* Ammonium Nitrogen 12 9 6 0 3 .772 .378 .300 .225 .119 Inorganic Nitrogen 12 9 6 0 3 1.500 1.084 .550 .447 .300 * Means underlined by the same li n e did not d i f f e r s i g n i f i c a n t l y according to Duncan's New Multiple Range Test at the 5% l e v e l . *1 H-OP C i-i fD RATE OF CARBON MINERALIZED (PERCENTAGE OF INITIAL TOTAL C MINERALIZED PER DAY) co po H- CO I T rt fD fD a o O H i o OO fo - H CO O p p Cu „ g Co I - 1 p Cu fD fD H i-i CO I—1 CO H-CO N g co rr . i-1 H-fD O co p Hi O i-i fD O s c O OP • r—' Co I—L CO •p- I • Hi H-I-i CD Co g T3 I—1 fD CD m m to O -n z o c CD RATE OF CARBON MINERALIZATION (PERCENTAGE OF INITIAL TOTAL C MINERALIZED PER DAY) 3 m m CO z o cz CD > Table 7. Summary of results of analysis of variance and Duncan's New Multiple Range Test applied to the three-week means of rate of carbon mineralization (percentage of i n i t i a l t o t a l C mineralized per day) for a l l samples Rate of Carbon Mineralization weeks 0 3 6 12 9 means .585 .311 .161 .158 .152* * Means underlined by the same li n e did not d i f f e r s i g n i f i c a n t l y according to Duncan's New Multiple Range Test at the 5% l e v e l . 33. 2 _ 2 2 P 3 O O < _ l < 2 -/ i i •/Hi z UJ CD O rr i— o z < o rr: o 2 CD < Y-2 Ul O CC UJ CL 12 WEEKS OF INCUBATION Figure 8. Inorganic nitrogen accumulation for Douglas-fir samples, s i t e No. 5 3 4 . horizons accumulated nitrogen at a f a i r l y regular rate throughout the test (Figures 5 , 6 & 8 ; Appendices I I I , IV & V). The slowdown i n mineral nitrogen accumulation observed i n some samples could have been due to d e n i t r . i f i c a t i o n losses brought about by changes i n a c i d i t y , nutrient status or moisture content of the incut>ated samples. In Germany, Zb'ttl* a t t r i b u t e d s i m i l a r decreases to increased immobilization by fungi l a t e r i n the incubation. Quantities of carbon mineralized and inorganic nitrogen accumulated for each horizon were compared to pH and C/N r a t i o s to see i f strong l i n e a r r e l a t i o n s h i p s were evident. A strong l i n e a r c o r r e l a t i o n between pH and carbon mineralized or inorganic nitrogen accumulated i s not indicated by the data i n Table 8 and Figure 9 . This l i k e l y due to the organic nature of the samples and the va r i e t y of s i t e s sampled. Comparison of C/N r a t i o s with carbon and nitrogen values indicates that high carbon and nitrogen m i n e r a l i z a t i o n i s associated with low C/N r a t i o s . This r e l a t i o n s h i p i s strongest i n the comparison of inorganic nitrogen accumulated and C/N r a t i o for the F and H or Hi horizons (Table 8 ; Figure 1 0 ) . I f gross carbon m i n e r a l i z a t i o n can be used as an indicator of the rate of organic matter decomposition and thus, the rate of gross minera-l i z a t i o n of organic nitrogen (Zb'ttl,-. 1 9 6 0 ) , then for Douglas-fir L , F and H or H i horizons r e s p e c t i v e l y , 2 3 . 2 , 1 5 . 6 and 1 3 . 7 7 > of the i n i t i a l t o t a l nitrogen was mineralized during the twelve-week test (table 4 ) . Of t h i s , only 0 . 4 , 1 . 5 and 3 . 8 7 o r e s p e c t i v e l y , of the i n i t i a l t o t a l nitrogen was recovered as inorganic nitrogen. This represents 9 8 . 3 , 9 0 . 4 and 7 2 . 2 7 , immobilization for the L , F and H or Hi horizons r e s p e c i t v e l y . The bulk of the mineralized nitrogen must be assumed to have been immobilized with some losses to d e n i t r i f i c a t i o n . For alder, the gross nitrogen mineralized Table 8. Summary of correlation coefficients r e l a t i n g C.N ratios and pH to carbon mineralized (percentage of i n i t i a l t o t a l C) and inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l nitrogen) for a l l samples Horizon L F H or Hi Element N C N C N C " r va 1 UP. C/N - .622 .709 - .809 - .243 - .883 - .627 pH + .212 + .196 - .374 + .544 - .064 + .234 36. 60 50 o -j o h-Q i i i _J N < -J h-< i cc ± Ixl Z Ix. i ° LU Z CD ° ^ m h-cc z < ixl o o cc Ixl 0_ 40 30 20 t 10 -o A A oA o A o F A H and Hi o A o o 0 1 ' 1— 1 1 L 3 4 5 6 7 8 pH Figure 9. Carbon mineralized plotted against pH for a l l samples p-oo c I-i fD l-h I—I O 3 i-l O i-i fo 0 0 i—1 3 P* CD o fo 3 3 13 P* I-i o 0 0 fD 3 Co n n I fD Cu INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) Ol o II ro po oo OJ I O x T T T ro o T =n o Q Q. CM 00 00 I ro ro OJ X rt fD Cu Co 0 0 Co P-3 co 33 > O X Q Q. X 3 i-i Co P-o O 33 3) r 1 1 3 CO CO £ o ? P m m oo o > m cn o ->j o _L ro * cn INORGANIC NITROGEN ACCUMULATED (PERCENTAGE OF INITIAL TOTAL N) oo would approximate 50.8, 17.5 and 19.4%, of the t o t a l nitrogen, while the net nitrogen accumulated would average 4.4, 5.5 and 14.3% for the L, F and Hi horizons r e s p e c t i v e l y . This represents 91.3, 68.6 and 26.3% immobilization for the L, F and Hi horizons r e s p e c t i v e l y . In order to suggest the r e l a t i v e s i g n i f i c a n c e of each horizons i n terms of quantity of nitrogen accumulated, rather than percentage of i n i t i a l t o t a l nitrogen accumulated, the horizon thicknesses (Table 1) and an assumed bulk density of 0.13 for forest f l o o r material were used to c a l c u l a t e the kg/ha of nitrogen released i n inorganic forms, p o t e n t i a l l y a v a i l a b l e to higher plants. It is r e a l i z e d that incubation r e s u l t s cannot be extrapolated d i r e c t l y to the f i e l d but nevertheless the derived values are useful for comparison. Results are shown i n Table 5 and i t i s evident that the H and H i horizons are by far the most important horizons i n terms of a b i l i t y to supply inorganic nitrogen for tree n u t r i t i o n . Values for Douglas-fir L, F and H or H i horizons average 0.1, 9.6 and 13.6 kg/ha while comparable alder values are 1.8, 26.8 and 96.3 kg/ha. 39. CONCLUSIONS 1. Limestone parent materials had a pronounced effect on calcium content of forest f l o o r s . Other effects of parent materials on forest floor composition were obscure. 2. Carbon concentration of forest floors generally decreases with depth, except i n mor humus-. In most f l o r e s t f l o o r s , magnesium concentration increases with depth, while potassium concentration decreases with depth. 3. Alder Hi horizons have r e l a t i v e l y low calcium contents except on limestone parent materials. In conifer forest f l o o r s , the carbon/nitrogen r a t i o decreases with depth, but i n alder forest f l o o r s , the C/N r a t i o tends to be low, and more constant with depth. 4. Carbon mineralization rates i n alder L horizons are greater than i n Douglas-fir L horizons, but mineralization rates i n F and i n Hi horizons are comparable for both species. 5. Mineral nitrogen accumulation, as a percentage of t o t a l nitrogen content, i s generally higher for H or Hi than L or F horizons. 6. In alder t y p i c a l moders, most of the mineral nitrogen i n the L horizons i s i n the ammonium form; i n F and Hi horizons, more tends to accumulate as n i t r a t e . 7. Even under the uniform favorable incubation conditions of the controlled environment chamber, mor forest floor materia3s decomposed s i g n i f i c a n t l y more slowly than their raw moder or mull counterparts, as evidenced by C0£ production measurements. 8. In mors, l i t t l e mineral nitrogen accumulated, and most ( i f not a l l ) of the mineral nitrogen occurred i n the ammonium form. 9. The probability of d e n i t r i f i c a t i o n losses occuring i n these incubation studies seems high for several reasons: (1) common occurrence 40. of nitrification,(2) absence of higher plant sinks for mineralized nitrogen, and (3) a tendency for anaerobic microsites to exist under the imposed conditions of temperature and moisture regime. Presumptive evidence for denitrification losses includes declining mineral nitrogen accumulation rates accompanying relatively constant carbon mineralization rates after several weeks of incubation. 41. LITERATURE CITED 1. B a l c i , A.N. 1963. Physical, chemical and hydrological properties of certain Washington forest floo r types. Ph.D. thesis, Univ. of Washington, Seattle, 192 p. 2. Bernier, B. 1968. Descriptive outline of forest humus-form c l a s s i f i c a t i o n . Proc. of the 7th meeting of the National S o i l S c i . Comm. of Canada. University of Alberta, Edmonton. p. 1391154. 3. Black, C.A. ed. 1965. Methods of s o i l analysis. Part 2. Agron. No. 9. p. 1171-1175. 4. Bollen, W.B., Chi-Sen Chen, K.C Lu and R.F. Tarrant. 1963. Influence of red alder on f e r t i l i t y of a forest s o i l : microbial and chemical effects. Oregon State Univ., School of Forestry. Research B u l l . 12. 61 p. 5. Bremner, J.M. 1965. Nitrogen a v a i l a b i l i t y indices. In C.A. Black ed. Methods of s o i l analysis. Part 2. Agron. No. 9. p. 1324-1345. 6. Brooke, R.C. 1965. Vegetation-environmental relationships i h the subalpine moutain hemlock zone ecosystems. Ph.D. thesis, the Univ. of B r i t i s h Columbia, Vancouver. 225 p. 7. Cole, D.W. 1963. Release of elements from the forest floor and migration through associated s o i l p r o f i l e s (a lysimeter study). Ph.D. thesis, Univ. of Washington, Seattle. 109 p. r 8. Harmsen, G.W. and D.A. Van Schreven. 1955. Mineralization of organic nitrogen i n s o i l . Adva. Agron. 8:299-398. 9. Hoover, M.D. and H.A. Lunt. 1952. A key for the c l a s s i f i c a t i o n of forest humus types. S o i l S c i . Soc. Amer. Proc. 16:368-370. 10. Jackson, M.L. 1958. S o i l chemical analysis. Prentice-Hall Inc., Englewood C l i f f s , N.J. 498 p. 42. 11. Lindner, R.C. and CP. Harley. 1942. A rapid method for determination of nitrogen i n plant tissue. Science. 96:565-566, 12. McMinn, R.G. 1957. Water relations in the Douglas-fir region on Vancouver Island. Ph.D. thesis, the Univ. of B r i t i s h Columbia, Vancouver. App. IV, p. 20. 13. Mork, E. 1938. Omsetningen i humusdekket ved f o r s k j e l l i g temperatur og fuktighet. Medd. Norske Skogsforsjiksv. 6:179-224. 14. Z o t t l , H. 1960. Dynamik der Stickstoffmineralisation im organischen Waldbodenmaterial. Plant & S o i l . 13:166-182. APPENDIX I Cumulative carbon mineralized (percentage of i n i t i a l t o t a l C) Appendix I Cumulative carbon mineralized (percentage of i n i t i a l t o t a l C) Weeks Site and Horizon 3 6_ 9 12 Mors L F H L F Hi 6.8 2.7 1.9 7.5 2.4 2.4 12.2 4.6 2.8 11.2 4.2 3.9 16.7 6.4 3.7 14.0 6.1 5.7 18.7 8.6 4.3 1.7.8 7.1 6.8 Raw Moders 3 L F Hi 4 L F Hi 5 L F Hi 6 L F Hi 7 L F Hi 8 L F Hi 5.7 4.1 3.1 13.1 6.9 10.1 10.9 5.9 .5.7 11.6 5.8 5.0 10.8 6.0 4.6 16.8 7.1 5.9 8.5 6.1 4.9 18.6 11.4 16.9 16.7 9.5 10.3 17.4 11.1 99; 5 14.6 9.2 7.2 24.3 12.1 9.7 11.1 8.1 7.1 23.4 15.1 21.4 21. 11. 12. 22.0 14.6 12.0 17.9 12.8 10.6 30.3 15.9 12.0 12.2 10.4 8.6 25.8 17.4 26.5 25. 14. 16. 26. 17. 15. 20.3 15.2 16.2 35.9 21.9 15.9 M u l l - l i k e Moders and Mulls 9 L F 10 L F 11 L F 8 ,2 ,7 6.3 7.1 8.8 6.0 11.6 12.6 10. 11. 13.0 10.6 14.3 17.3 13.9 15.5 18.3 13.7 16.5 19.8 16, 18, 23.5 1.7.8 continued. Appendix I continued Cumulative carbon mineralized (percentage of i n i t i a l t o t a l C) Weeks Site and Horizon 3 6 9 12 12 L 15.3 26.4 34.5 40.1 F 6.8 11.4 16.5 19.0 Typical Moders 13 L 26.6 37.0 42.4 49.2 F 6.3 10.8 13.3 17.2 Hi 5.9 9.3 11.2 15.6 14 L 27.9 39.2 44.0 49.7 F 5.5 8.5 9.8 10.5 Hi 2.9 4.6 5.5 6.8 15 L 29.8 41.7 48.0 53.4 F 12.3 18.0 22.1 24.9 Hi 11.2 20.6 29.2 35.8 46. APPENDIX I I Rate of carbon mineralization (percentage of i n i t i a l t o t a l C mineralized per day) Appendix II Rate of carbon m i n e r a l i z a t i o n (percentage of i n i t i a l t o t a l C mineralized per day) Weeks Site and Horizon 0 3 6 9 12 Mors 1 L .31 .27 .19 .19 .10 F .11 .11 .05 .07 .10 H .04 .10 .03 .04 .03 2 L .29 .19 .11 .14 .18 F .04 .10 .10 .08 .05 H .04 .10 .05 .08 .05 Raw Moders 3 L .41 .18 .10 -.13 .05 F .17 .21 .05 .09 .10 Hi .09 .14 .07 .07 .07 4 L .79 .38. .10 .18 .12 F .34 .27 .21 .16 .11 Hi .41 .43 .12 .20 .24 5 L .49 .42 .20 .20 .20 F .29 .29 .06 .09 .14 Hi .31 .19 .17 .08 .16 6 L .79 .32 .25 .19 .20 F .23 .31 .13 .18 .13 Hi .17 .26 .13 .10 .16 7 L .38 .31 .10 .14 .11 F .27 .27 .03 .16 .11 Hi .19 .17 .04 .17 .27 8 L 1.71 .48 .20 .26 .27 F .34 .31 .21 .17 .28 Hi .36 .29 .08 .08 .18 Mul1-1 ike Moders and Mulls 9 L .73 .24 .10 .14 .10 F .35 .36 .11 .22 .12 10 L .24 .27 .20 .17 .10 F .40 .33 .16 .20 .13 1 1 L .41 .31 .27 .21 .25 F .26 .26 .19 .12 .19 48. Appendix I I continued Rate of carbon mineralization (percentage of i n i t i a l t o t a l C mineralized per day) Weeks Site and Horizon 0 3 6 9 12 12 L .52 .61 .48 . .37 .27 F .30 .30 .13 .22 .12 Typical Moders 13 L 3.60 .72 .34 .22 .32 F .44 .25 .18 .12 .18 Hi .27 .21 .09 .09 .21 14 L 3.20 .76 .48 .18 .27 F .33 .26 .12 .04 .03 Hi .14 .12 .06 .03 .06 15 L 3.00 .75' .35 .24 .26 F .72 .43 .30 .20 .13 Hi .50 .49 .27 .20 .31 APPENDIX III Nit r a t e nitrogen accumulated (percentage of i n i t i a l t o t a l N) Appendix I I I Nitrate nitrogen accumulated (percentage of i n i t i a l t o t a l N) Weeks Site and Horizon 0 3 6_ 9 12 Mors L F H .1 .1 0 .2 0 .1 0 0 0 .0 .9 .4 .7.5' ,2 .1 L F H .2 .1 .0 0 0 0 0 0 0 .3 .1 .3 3 L F Hi 4 L F Hi 5 L F Hi 6 L F Hi 7 L F Hi 8 L F Hi .3 .1 0 .4 .2 .5 0 .1 .2 .1 0 .3 .3 .1 .2 .4 .1 .2 Raw Moders 0 0 0 .2 .2 .3 0 0 .1 0 0 0 .1 0 .5 .1 0 .3 0 .1 .2 .4 .3 .7 .2 .1 .6 .1 0 0 .2 .1 .7 .2 .1 .2 .2 .1 .2 .9 .9 1.6 1.1 .6 1.1 .2 .1 .1 .6 .2 .9 .3 .2 2.1 .1 .1 2.8 .2 .2 3.7 .4 .2 1.9 .2 1.3 .1 .1 0 1.3 .1 .2 5.3 M u l l - l i k e Moders and Mulls 9 L F 10 L F 11 L F 0 .1 .4 0 .1 0 0 0 . 0 0 1.9 .9 .2 .5 0 0 2.1 0 .1 .8 .1 .2 .9 .5 0 3.7 .1 0 .9 .3 Appendix I I I continued Nitrate nitrogen accumulated (percentage of i n i t i a l t o t a l N} Weeks Site and Horizon 0 3_ 6 9 12 12 L 1.4 .5 0 1.4 .4 F .1 .4 0 1.2 .3 Typical Moders 13 L . 1 0 0 .1 .2 F .3 1.3 2.8 2.9 5.5 Hi 1.6 6.1 . 7.4 7.7 13.9 14 L .1 0 :2 .3 .3 F 1.1 2.1 3.0 3.6 5.4 Hi 2.2 3.0 4.2 3.9 6.5 15 L .6 . 1 0 .5 .1 F 115 .1 .4 2.0 4.6 Hi 3.9 1.8 5.6 10.0 18.1 52. •' :» APPENDIX IV i Ammonium ni t r o g e n accumulated (percentage of i n i t i a l t o t a l N) Appendix IV Ammonium nitrogen accumulated (percentage of i n i t i a l t o t a l N) Weeks Site and Horizon 0 3 __6 9 12 Mors. 1 L .1 0 .2 0 .2 F .4 .4 1.7 2.6 3.5 H .1 .3 1.2 1.6 2.1 2 L 0 0 .2 :0 .1 F .1 0 .2 0 .1 H . 1 0 1.1 .8 1.3 Raw Moders 3 L 0 .1 .1 0 .1 F .2 .1 .3 .6 1.6 Hi .6 .5 .7 2.1 3.4 4 L .2 0 0 0 0 F .2 0 0 .1 .4 Hi 1.0 1.3 2.3 2.8 6.6 5 L 0 0 0 0 .2 F .1 .1 0 .1 .1 Hi .2 .5 .2 .3 1.0 6 L .2 .1 .1 .2 .1 F .2 .1 .1 .1 .2 Hi .2 0 .2 .3 .3 7 L .1 0 0 0 .1 F .2 0 0 0 .1 Hi .2' . 1 0 0 .2 8 L .2 0 0 0 .1 F .1 0 0 0 0 Hi .3 0 0 0 .1 M u l l - l i k e Moders and Mulls 9 L .1 0 .1 0 0 F .4 .1 .6 .4 .2 10 L .2 0 .1 0 0 F .2 .1 .2 0 0 Appendix IV continued Ammonium nitrogen accumulated (percentages.? of i n i t i a l t o t a l N) Weeks Site and Horizon 0 3 6 9 12 11 L .3 0 0 0 .2 F .4 0 0 0 .3 12 L .3 0 0 0 . 2 F .3 0 0 .1 .3 Typical Moders 13 L .2 1.9 . 4.5 4.6 5.3 F .4 .1 .2 .1 .2. Hi .2 0 .2 .5 2.4 14 L .1 6.0 7.9 8.0 7.1 F .8 .1 .4 .5 .6 Hi .3 .2 .6 1.1 U-8 15 L .3 .1 0 .1 ,1 F .2 0 0 0 .1 Hi . 2 0 0 0 .2 APPENDIX V Inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) Appendix V Inorganic nitrogen accumulated' (percentage of i n i t i a l t o t a l N) Weeks Site and Horizon 0 3 6 9 12 Mors 1 L .2 .2 .2 l i O .7 F .5 .4 1.7 3.5 3.7 H .1 .4 1.2 2.0 2.2 2 L .2 0 . 2 .3 .1 F .2 0 .2 .1 .1 H 1.1 0 1.1 1.1 1 . 5 Raw Moders 3 L .3 .1 .1 .2 .2 F .3 .1 .4 .7 1.7 Hi .6 .5 .9 2.3 6.2 4 L .6 .2 .4 .9 .2 F .4 .2 .3 1.0 .6 Hi 1.5 1.6 3.0 4.4 10.3 5 L 0 , 0 .2 " 1.1 .6 F .2 .1 .1 .7 .3 Hi .4 .6 .8 1.4 2.9 6 L .3 .1 .2 .4 .3 F .2 .1 . .1 .2 1.5 Hi .5 0 .2 .4 .4 7 L .4 .1 .2 .6 .2' F .3 0 .1 .2 .1 Hi .4 - 6 - 7 - 9 1-5 8 L .6 .1 .2 .3 .2 F .2 0 .1 .2 .2 Hi .5 .3 1.2 2.',1 5.4 M u l l - l i k e Moders and Mulls 9 L .1 0 .3 .'1 0 F .5 .1 1.1 1.2 3.9 10 L .6 0 .1 .1 .1 F .2 .1 .2 .2 0 Appendix V continued Inorganic nitrogen accumulated (percentage of i n i t i a l t o t a l N) Weeks 0 3 6 9 Site and Horizon 12 l l - L F 12 L F 13 14 L F Hi L F Hi 15 L F Hi ,4 '.4 1.7 .4 .3 .7 1.8 .2 1.9 2.5 .9 1.7 4.1 .9 1.9 .5 .4 •2.1 0 0 0 Typical Moders 1.9 1.4 6.1 6.0 2.2 3.2 .2 .1 1.8 4.5 3.0 7.6 8.1 3.4 4.8 0 .4 5.6 2.9 1.5 1.4 1.3 4.7 3.0 8.2 8.3 4.1 5.0 .6 2.0 10.0 1.1 .6 .6 .6 5,5.: 5.7 16.3 7.4 6.0 8.3 .2 4.7 18.3 Appendix IV Outline of the c l a s s i f i c a t i o n used i n characterizing horizons and forest f l o o r s * Horizons L - L i t t e r , freshly f a l l e n leaves and other plant debris, the structure of which is not altered by decomposition. F - An organic horizon consisting mostly of s l i g h t l y decomposed plant remains s t i l l recongnizable as to their o r i g i n . H - An organic horizon characterized by advanced decomposition, the structure or o r i g i n of the plant materials for the most part being unrecognizable. Hi - An organic horizonwith considerable mineral matter intermixed. Transition to the mineral s o i l i s gradual. Forest Floor Types Mors L, F and H horizons present, p r a c t i c a l l y no mixing of organic matter with mineral s o i l . Moders L, F and Hi horizons present (no Hi i n mull-like moders), the Hi intermixed with mineral s o i l but organic and mineral particles exist as d i s t i n c t elements. Subtypes of Moders Typical Moder - (fine mull) Generally formed under mixed or hardwood forests, with a thi n F and a predominant Hi. Raw Moder - (duff mull) Has a comparatively thick F horizon and i s t r a n s i t i o n a l to a mor. M u l l - l i k e Moder - (sand mull) Resemble mulls but lack the intimate mixture of organic matter and mineral s o i l of mulls, has a thin F and a thick Hi or Ah. Mulls No H or Hi, the Ah an intimate mixture of organic matter and mineral s o i l . *After Bernier, 1968 and Hoover and Lunt, 1952. 

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