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UBC Theses and Dissertations

The absorption of inorganic nutrients by plants treated with sulphur dioxide 1937

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THE ABSORPTION OF IHORGAMIC MDTRIEMIS BY PLANTS TREATED WITH SULPHDR DIOXIDE Wilfred Robert Jack A Thesis submitted for the Degree of MASTER OF ARTS i n the Department of BOTANY The University of B r i t i s h Columbia A p r i l , 1937 THE ABSORPTION OF INORGANIC NUTRIENTS BY PLANTS TREATED WITH SULPHUR DIOXIDE. I The Problem Defined. II The Environmental Factors and the Plant Stock. I I I The Experimental Conditions. IV The Results of the Experiments. V Discussion. VI Acknowledgements. VII Bibliography. The effect upon vegetation of the gaseous wastes from i n d u s t r i a l enterprises, p a r t i c u l a r l y smelters, has re- ceived considerable attention in this century both from the legal and from the s c i e n t i f i c points of view. It was soon agreed that this effect was caused by the presence of gaseous sulphur dioxide in the atmosphere. For a summary of investigations upon this subject prior to 1915 the reader i s referred to the 528 pages published by the Selby Smelter Commission ( l ) . Such s c i e n t i f i c investigations have shown that the conditions under which injury to vegetation from sulphur dioxide takes place are determined primarily by the concen- tration of the gas, the duration of the exposure, and the humidity of the a i r . Secondary factors are the characteristic s u s c e p t i b i l i t y of the species, the l i g h t conditions, and other environmental conditions of atmosphere and s o i l . On these conditions a large amount of data has been compiled. It i s not the purpose of this paper to disprove any of these findings. However, i t has been the purpose of these exper- iments to determine the absorption of inorganic nutrients by treated plants, and. to see what conclusions might be made regarding the metabolism of the plants from t h i s point of view. The plant environment i s so complex, with so many variable factors entering that i t would be impossible to get data on a l l combinations i n a problem of this kind. The method followed has been the usual relative study employing controls. In a l l factors excepting sulphur dioxide i n the atmosphere,' the control plants-were developing i n an environ- ment ide n t i c a l with that of the experimental plants . Buring treatments with the gas, a i r was supplied in continuous flow to the plants in specially constructed a i r - t i g h t cabinets by blowers ("Sirocco" blowers, driven by General E l e c t r i c motors, 1/20 H.P., 110 Volts, 1.3 Amps., 1140\R'.P.M.). The a i r flow delivered by such blowers may be conveniently regulated by adjusting a s l i d i n g panel over the aperature in a galvanized iron box connected t o t h e blower intake. To determine the volume of the a i r flow and to main- tain equality between control and fumigated cabinets a calib- rated anemometer (Short & Mason, Ltd., London, "Biram's !b. 3132") was introduced into the a i r supply pipe through an ai r - t i g h t s l i d i n g panel. The linear velocity was then deter- mined.for an interval of time measured by a stopwatch. This l i n e a r T e l o c i t y m u l t i p l i e d by the cross-section of the supply pipe gave the volume of a i r supplied. The a i r furnished to the experimental cabinet was passed through a "mixing chamber", a large galvanized i r o n box with b a f f l e plates i n i t . A tube leading to the a i r entry end of t h i s chamber c a r r i e d the sulphur dioxide gas f o r intimate mixture i n the concentrations desired. The sulphur dioxide f o r the treatments was obtained i n small c y l i n d e r s from the manufacturers, Ansul Chemical Company, Marinette, Wisconsin, through the Central S c i e n t i f i c Company. These 6 l b . c y l i n d e r s contain l i q u i d sulphur dioxide of extreme p u r i t y , no trace of sulphur t r i o x i d e heing found. They are equipped with a needle valve f o r r e g u l a t i n g the flow of gas from the c y l i n d e r s . To measure the flow of gas through a needle valve, a meter of the type described by Benton (2) may be used. This a r t i c l e discusses the t h e o r e t i c a l 'and p r a c t i c a l .consid- • erations which l e a d to the a p p l i c a t i o n of P o i s e u i l l e ' s formula (for the fl o w of l i q u i d s ) to the flow of gases through cap- i l l a r y tubing, and c a l c u l a t i o n of volume from the pressure d i f f e r e n c e . In t h i s way a U-ma,nometer of the i n c l i n e d gauge type w i t h a s e a l e d - i n c a p i l l a r y tube between the arms has been used. The manometer was f i l l e d with l i q u i d petrolatum., f o r low concentrations i t has heen found more convenient to use c a p i l l a r y tubing leading from the c y l i n d e r outlet into, a r e s e r v o i r of petrolatum w i t h t h e outlet above the surface of the l i q u i d . Counts of gas-bubble rates of flow lip through 6. the petrolatum correlated with concentration determinations gave a useful empirical method of adjusting the concentration to the desired amount. A constant pressure from the cylinder was maintained by temperature control.. A lined gas-metering box was con- structed. It contained the cylinder almost Immersed in a water-bath; the c a p i l l a r y U-manometer; and a thermo-regulator (Geneo De Khotinsky) governing a 100 Watt lamp connected to supply heat when needed. To ensure purity of ;air supply and to guard against any possible accident, the gas-meter box was kept in an ad- joining room and the outlet passed through the w a l l to the mixing box. The frequent and accurate determination of the sulphur dioxide content i n the atmosphere during any treatment i s . e s s e n t i a l . The most r e l i a b l e method yet devised i s the sampling system, of Thomas and Abersold, (3).." In this method the gas i s oxidized in absorbers by dilute hydrogen peroxide and sulphuric acid solution, and the changing conductivity i s measured upon a Leeds and Hbrthrup recording Wheat stone bridge. The special apparatus for t h i s method was not a v a i l - able for these experiments. But determinations of low con- centrations of sulphur dioxide- using the methiod described by G r i f f i n and Skinner ( 4 ) are accurate * and the necessary apparatus i s easily assembled. This l a t t e r method was used throughout. The apparatus -consisted of two absorbers, ah a i r flowmeter of the U-manoineter type, a suction pump, a.nd small pressure-equalizing tank. The a i r flowmeter was calibrated by means of a wet meter which in turn had been checked against a standard "prover". The manometer readings were determined for a wide range on either side of the optimum flow, which i s about 1 gram-molecular volume of gas in 3 minutes. The arrangement for calibrating the flow rate is i l l u s t r a t e d in the accompanying photograph. The absorbers contain 100 c c . of an iodine- potassium iodide-starch solution about 0.00003 N in iodine. Through one absorber containing this solution a metered volume of a i r is drawn as a "blank" using a soda-lime tower. Through the other absorber the same volume of a i r i s drawn from the 8. e x p e r i m e n t a l c a b i n e t . The s o l u t i o n s a r e t h e n d r a i n e d i n t o f l a s k s a n d t i t r a t e d t o t h e same l i g h t - b l u e e n d - p o i n t w i t h a s t a n d a r d s o d i u m t h i o s u l p h a t e s o l u t i o n , 0 . 0 0 1 C H t o 0 . 0 0 1 5 l i . The t i t r a t i o n i s made by t h e u s e o f a s m a l l p r e c i s e b u r e t w h i c h may be r e a d t o 0 . 0 2 c . c . The d i f f e r e n c e b e t w e e n t h e two t i t r a t i o n s r e p r e s e n t s t h e e q u i v a l e n t o f t h e s u l p h u r d i o x i d e a b s o r b e d . The c o n c e n t r a t i o n i n p a r t s p e r m i l l i o n may be c a l c u l a t e d d i r e c t l y , s i n c e 1 c . c . o f 0 . 0 0 2 l\ s o d i u m t h i o - s u l p h a t e s o l u t i o n i s e q u i v a l e n t t o 1 p a r t p e r m i l l i o n o f s u l p h u r d i o x i d e i n 1 g r a m - m o l e c u l a r v o l u m e o f a i r . The a r r a n g e m e n t o f t h e a p p a r a t u s f o r a d e t e r m i n a t i o n i s shown i n t h e a c c o m p a n y i n g p h o t o g r a p h . '-. As has been mentioned, the other atmospheric condit- ion of primary importance in;gas treatments i s the humidity. This i s a very d i f f i c u l t factor to control. In a l l treatment a record of the relative humidity has been kept. Temperature of the atmosphere has also been re- corded. The lig h t factor was variable during two experiments The plants i n t hese experiments were grown i n tthe greenhouse, under the solar illumination received by t h i s part of the P a c i f i c coast i n the late f a l l . There i s a wide variation of Tight from day to day: clear bright sunlight, diffuse l i g h t on foggy days, or very l i t t l e l i g h t i n cloudy weather. The other experiments were carried out under " a r t i f i c i a l " illum- ination i n specially constructed cabinets. Excepting for the gradual decrease in intensity of the radiation from the bulbs, the l i g h t .factor was similar for each 24-hour period. The construction of the cabinets i n which the lig h t factor was controlled followed the general plan of Davis and Hoagland ( 5 ) . One of the modifications adopted by Swain and Johnson (6) was introduced, however: theolights.were placed d i r e c t l y over the plants. Each cabinet followed the same pattern: a counterpoised l i f t piece (6 f t . long x 2 f t . wide x 5 f t . high), rested upon a f i x e d base ( 6 f t . long x 2 f t . widejx 2 f t . h i g h ) . The entire construction was a i r - t i g h t . The top, sides, and ends of each l i f t piece were of f a i r l y heavy high-grade glass. Lights were seated i n 52 cm. reflec- tors and fixed inppo-sitio.n. 2 feet above the cabinet top. 10, The lights were controlled by a time switch. A i r cir c u l a t i o n was provided for through an intake in the base and outlets at the cabinet top. Some of the details are i l l u s t r a t e d in the accompanying photographs. 11. 12. The plants w.ere grown in water culture solution. The nutrient solution used was the "Rubideux" solution des- cribed by Eaton (7). The constituents of this solution and their concentration are as follows: Millimoles Grams per Constituent per l i t e r . 10G l i t e r s . Calcium n i t r a t e , Ca(¥0 3) 2.4H 20 4 9 4 Potassium n i t r a t e , K N O 3 3 30 Ammonium sulphate, (IH^gSG^ 2 27 Magnesium sulphate, MgS0^.7H20 2 4 9 Potassium acid phosphate, K H 2 P O 4 0.2 - 3 Boric acid, H 3 B O 3 _ 0.6 Manganese chloride, MnC^^H^Q;; - 0.1 Zinc sulphate, Z n S O 4 . 7 H . 2 O ' 0.04 Iron was made available to the plants "by addition of the t a r t - rate (freshly prepared 0.5 percent solution) in small amounts at frequent intervals as required. The concentration was maintained by replacement of nutrients as.these were absorbed, and by changing the whole solution. The hydrogen ion concen- tration varied from p H 6.0 to 6.5. This solution has been used in preference to the older widely-used Hoagland's solution because i t seems to possess the advantages described by the author. The supply of some of the nitrogen as ammonium tends to maintain a better ion balance, the 'low-level of phosphate makes i t easier to maintain available iron. The solution containers were wide-mquth glass jars of 13. 1.75 l i t e r volume (2-quart Mason) . The tops were closed "by corks with 5 holes for plants and an opening for additions of water. Five cereal seedlings were grown i n each j a r , and enough jars were used to make a t o t a l of 110 plants for both control and treated i n each experiment. The plant stock used in these experiments was barley. Barley has been widely used i n experimental work of this kind because i t grows with vigor i n balanced nutrient solutions of pH 5.5 - 7.0. The variety grown for experiment was Duck- b i l l , the purest line .seed obtainable from the Department of Agronomy, University of B r i t i s h Columbia. The importance of homogeneous stock i n experimental work has been r i g h t l y stressed by many investigators., The i-seed was soaked for 24 hours i n culture solution at 20.5°C. It was then placed on mesh screen over culture solution to germinate i n a medium li g h t intensity. .When the seedlings were 9 cm. i n length, a uniform selection was transplanted to the culture jars. The importance of guarding against plant diseases such as rusts and smuts has been recognized, and the plants were free from infection. .. Measures were taken to prevent infestation by plant parasites such as aphids. 1 4 . I l l The conditions under which treatments took place, and the environmental factors are recorded i n the following pages, Duration; .Experiment 1. Sulphur Dioxide Records:- F i r s t Treatment: 27 days after dry seed was soaked. Healthy plants with 3-4 leaves. 6 hours gas history. Treatments on 2 successive days. Each treatment of 3 hours duration. Time of day: morning. Average - 0.40 p.p.m. Maximum - 0.50 p.p.m. Minimum - 0.30 p.p.m. Very high, 90-100% relative humidity, 65-75° F. oQ% of the total,, leaf area. Concentration: Humidity: Temperature: Vis i b l e Injury Env i r onment Re e o r d s : - Light:.. Sunlight in late f a l l . 15. L i g h t : Plants were grown i n a greenhouse Temperature: Average Maximum - 105° Pv Minimum - 55° P. Humidity: Average (high) Maximum - 100^ r e l a t i v e humidity. Minimum - 10% r e l a t i v e humidity. The experiment was discontinued 56 days a f t e r the dry seed was soaiked.. . Experiment 2. Sulphur Dioxide Records F i r s t Treatment: 27 days a f t e r dry seed was soaked. Healthy plants with 3-4 leaves. Duration: 12 hours gas h i s t o r y . 3 treatments at 10-day i n t e r v a l s . Time of day: morning. Concentration: Average - 0.30 p.p.m. Maximum - 0.33 p.p.m. Minimum - 0.27 p.p.m. Humidity: Temperature: V i s i b l e Injury: Environment Records:- L i g h t : Temperature: Very high, 90-100% r e l a t i v e humidity, 65-80° P. 5% of the t o t a l l e a f area. Sunlight i n l a t e f a l l . P l a nts were grown i n a greenhouse Average ------ Maximum - 105° P. 16. Temperature: Minimum - 55° F. Humidity: Average Maximum - 100% relative humidity. Minimum - 70% relative humidity. The experiment was discontinued 56 days after the dry seed was soaked. Ebrperiment 3. Durat ion: Concentration Sulphur Dioxide Records:- F i r s t Treatments 15 days after dry seed was soaked. Healthy plants with 3-4 leaves. 480 hours gas history. Continuous treatment. 24 hours each day. Average - 0.27 p.p.m. Maximum - 0.41 p.p.m. Minimum - 0.18 p.p.m. Humidity: F a i r l y low. Usually a maximum of 60-62% relative humidity "before the illumination, then a decrease to a minimum of about 40% at the end of the illumination period. Temperature: F a i r l y high. Usually a minimum of about 67-68° F before illumination, then an increase to a maximum of about 90-94° F at the end of the illumination period. 17. Vi s i b l e Injury: None. Leaf colour of the exper- imental plants was a ligh t e r green than that of the control plants. Environment Records:- Light: Plants were grown in cabinets. Illumination from four 1000-Watt gas f i l l e d bulbs seated in 52 cm. r e f l e c tors at a distance of 7 feet. 16 hours illumination each day. Average -:84° P. Maximum Minimum - 66° P. Average - A9% relative humidity. •Maximum - 66% relative humidity. Minimum - 37% relative humidity. The experiment was discontinued 35 days after the dry.lseed was soaked. Temperature: 98° P. Humidity: Experiment 4. Sulphur Dioxide Records:- Pi r s t Treatment: 15 days after dry seed was soaked. Healthy plants with 3-4 leaves. Duration: 51 hours gas history. Treatments on 17 consecutive days. Each treatment of 3 hours duration. Treatment began 1 hour after the illumination had commenced. 18. Concentration; Humidity: Temperature: V i s i b l e Injury: Environment Records:- •Light: Temperature; Average - 0.36 p.p.m. Maximum -0.58 p.p.m. Minimum - 0.25 p.p.m. Medium - 55-70% relative humidity. 75-85° F. None. Plants were grown in cabinets. Illumination from three 1000-Watt gas f i l l e d bulbs seated in 52 cm. reflectors at a distance of 7 feet 16 hours illumination each day. Average - 78° F-. Maximum - 90 F. Minimum - 70° F. Humidity: Average - 59% relative humidity?. Maximum - 77% relative humidity. Minimum - 4 7% relative humidity. The experiment was discontinued 32 days after the dry seed was soaked. 1 9 . IV The results of the experiments have been recorded as y i e l d data and as analyses. These records are grouped i n tables in the following pages. The plants in experiment 4 had the least f i n a l green and dry weights. It seemed of interest to show the size of these plants. The accompanying picture was taken 12 days after fumigation commenced, or 5 days before the experiment was dis- continued . 20. Fa Me go..- 1. Yield Data. T i l l e r s per Plant. Green Weights (Grams per 100 Plants) •loisture (as %•) Dry Weights (Grams per 100 Plants) Sxperiment 1. Control 1.61 Leaves •Stems Roots Total 230 119 71 420 91.1 92.0 93.4 91.8 20.5 9.5 4.7 34.7 Treated 1.51 Leaves Stems Roots Total 168 94 65 327 89.2 93.0 93.9 91.2 18.1 6.6 4.7 28.7 Experiment 2. Control 1.26 Leaves Stems Roots Total 205 100 66 371 90.8 93.0 93.4 91.9 18 .8 7.0 4.4 30.2 Treated, 1.16 Leaves Stems Roots Total 177 94 63 334 90.0 93.1 93.4 91.5 17.7 6.5 4.1 28.3 21. Table Ho. 1 (continued). Yield Data. T i l l e r s Green Moisture Dry per Weights (as %) Weights Plant. (Grams (Grams per 100 per 100 Plants) Plants) Experiment 5.- Control 3.02 Leaves Stems Roots. Total 109 102 119 330 81.9 89.3' 93.5 88.4. 19.7 11.0 7.7 38.4 Treated 2.93 Leaves Stems Roots Total 102 99 109 '310 82.3 89.0 93.7 88.5 18.1 10.9 6.8 35.8 Experiment 4. Control 2.09 Leaves Stems Roots . Total 77.3 59.7 65.4 202.4 84.7 90.6 92.1 88.8 11.87 5.63 5.16 22.66 Treated 2.14 Leaves Stems Roots Total 77.0 61.1 65 .6 203.7 84*8. 90.7 92.1 88.9 11.73 5.77 5.23 22.63 22 « The transpiration by the plants has been measured as water added to keep the containers at l e v e l . The evaporation from blank containers has been determined. In t h i s way a net transpiration value for the plants "has been derived. Using these values a transpiration c o e f f i c i e n t has been calculated as follows, after that of Briggs and Shantz (8) j Transpiration Coefficient: The results of t h i s calculation are i n the next table Volume of water transpired. freight of dry materiel formed. Table Mo. 2 Experiment 1 Plants Control Treated Control Treated Control Treated Control Treated Transpiration"Coefficient 255 152 194 180 692 548 653 618 To determine the absorption of nutrients from the culture solution, analyses were made of the dry plant material. These analyses have been done according to the recognized -quantitative methods advocated by the Association of O f f i c i a l A g r i c u l t u r a l Chemists i n the publication (9) " O f f i c i a l and Tentative Methods.....", 4th edition, 1936. The results of these analyses are recorded i n the following table. 25. Plants Analysed. Table Ho. 3 As percent of dry plant material. Experiment 1 Control- Treated Ash Ca MgO K I (total) 18.14 1.19 0.79 7.78 1.98 0.85 6.IS 17.56 1.17 Q.71 7.54 1.71 0.76 5.72 Experiment 2. Control Treated 17.66 1.46 0.82 7.46 1.92 0.75 6.48 17.47 1.46 0.85 7.59 1.84 0.74 6.51 Experiment '3. Control Treated 18.11 1.42 0.64 7.38 2.06 1.02 6.61 18.16 1.27 0.53 6.73 2.84 0.95 5.87 Experiment 4. Control Treated 18.56 1.24 0.60 7.61 1.94 1.31 6.34 17.73 1.18 0.58 7.23 1.98 1.27 6.30 2 4 . The relation of the extent of r i s i b l e injury to the factors involved has been the subject of exhaustive research by many investigators. This work has been done chiefly under f i e l d conditions. The results are obtained by observing the extent and character of the injury, by measurements of y i e l d , and by correlating these with the experimental conditions. The results are compared with controls as standards. Inform- ation of this nature i s extensive, and has an all-important bearing upon the subject of sulphur dioxide effects. Growth of plants in culture solutions in a con- t r o l l e d environment and treated with low concentrations of sulphur dioxide has been studied by Swain and Johnson (6). This research shows careful study throughout and the authors reached the following conclusion: "The results of this study, indicate that wheat plants grown i n nutrient solutions under optimum conditions of a r t i f i c i a l l i g h t and humidity which were favorable to rapid and uniform growth, and which at the same time could be accurately controlled and recorded, w i l l tolerate an exposure to sulphur dioxide of several, hours daily in concentrations 25 below those at which ty p i c a l f o l i a r markings are produced with- out showing any signs of injurious actions in their general appearance, i n their rate of growth, or i n the dry weight of tissue which they develop." Studies have been made of the effects of sulphur dioxide exposure upon stomatal movement in plants to determine possible correlations. These morphological investigations are based upon the reasonable assumption that any injury to the plant organism takes place through the leaf stomata. The effect of exposure to sulphur dioxide upon the chemical composition of the growing plant has been studied ever since f o l i a r accumulation of sulphur compounds was f i r s t ob- served'. Correlations of sulphur content with the exposure have "been made. Data relating to the effect upon' carbohydrate metabolism and protein eontent has been compiled. The writer has been privileged i n observing an ex- tremely interesting study of the effect of sulphur dioxide treatments on the carbon dioxide-oxygen metabolism of plants, carried out "by Dr. M . Katz and associates. ( 1 0 ) In t h i s research the problem has been approached from the point of view of inorganic nutrient absorption through the roots. The assumption has been made that the chemical con- s t i t u t i o n , as shown by analysis, i s a measure of the nutrient absorption. Prom the results of experiments with wheat plants ( 1 1 ) , the writer reached the conclusion that the problem could only be considered when plants werejaot severely injured. The reasons for this are - that the chemical composition of plants may vary widely according to the stage of growth and, since the 26. study i s a r e l a t i v e one, i t would be unwise to increase the probability or error. The experimental conditions and re s u l t s have been recorded i n several tables above. The y i e l d data, transpiration coefficients and analyses have been grouped i n the following table. An accompanying table of r e l a t i v e values with the control as 100 has been made. The writer i s defend t h i s l a t t e r on either l o g i c a l or mathematical grounds. These tables may be conveniently referred to i n th i s discussion. V i s i b l e i n j u r y i s not dependent upon the concentration of the gas alone, as has been shown by the c l a s s i c a l experiments i n this f i e l d . T h i s f i n d i n g i s reaffirmed by these experiments. Humidity i s a factor of primary importance. At 90 - 100$ humidity, v i s i b l e injury was produced by sulphur dioxide at concentrations of 0.40 p.p.m. and 0.50 p.p.m.j while at 37 - 66$ r e l a t i v e humidity, no injury was produced by 0.27 p.p.m.j and at 55 - 70$ humidity, no injury was produced by 0.56 p.p.m. The duration factor i s also shown; 6 hours on 2 successive days at a concentration of 0.40 p.p.m. produced v i s i b l e injury on 30$ of the t o t a l l e a f area of plants i n the 3-4 lea f stage; but 12 hours on 3 days at 10-day i n t e r v a l s with a concentration of 0.30 p.p.m. produced v i s i b l e i n j ury on only 5$ of the t o t a l l e a f area. Where no v i s i b l e injury was produced, the effects of duration are seen i n comparing the dry weight y i e l d s . 27. Exper. 1 Table Hp. 4 Exper. 2 Exper. 5 C. Exper. 4 Absolute Values. T i l l e r s Green weight % Moisture Dry weight Transpiration % Ash % Calcium % Magnesium % Potassium % Sulphur % Phosphorus % Mitrogen 1.61 1.51 1.26 1.16 5.02 2.93 2.09 2.14 420 327 371 334 350 310 202.4 205.7 91.8 91.2 91.7 91.5 88.4 88.5 88.8 88.9 34.7 28.7 30.2 28.3 38.4 55.8 22.7 22.6 235 152 194 180 692 548 653 618 18.14 17.56 17.66 17.47 18.11 18.16 , 18.56 17.73 1.19 1.17 1.46 1.46 1.42 1.27 1.24 1.18 0.79 0.71 0.82 0.83 0.64 0.53 0.60 0,58 7.78 7.54 7.46 7.59 7.38 6.73 7.61 7.23 1.98 1.71 1.92 1.84 2.06 2c 84 1.94 1.98 0.85 0.76 0.75 0.74 1.02 0.95 1.31 1.27 6.13 5.72 6.48 6.51 6.61 5.87 6.54 6,30 Relative Values. (Control as 100) T i l l e r s Green weight % Moisture Dry weight Transpiration % Ash % Calcium $ Magnesium % Potassium % Sulphur % Phosphorus /S Hitrogen 100 93,7 100 92,1 100 97.0 100 102.4 100 77.9 100 90.0 100 95.9 100 100.6 100 99.3 100 99.8 100 100.1 100 100.1 100 82.7 100 93.7 100 93.2 100 99.9 103 65.0 100 95.0 100 80.0 100 95.0 100 95.7 100 98.9 100 100.3 100 95.5 100 98.3 100 100.0 100 89.5 100 95.1 100 89.9 100 101.2 100 82e 8 100 96.6 100 96,8 100 97.8 100 91.2 100 95.0 100 86.4 100 95.8 100- 157.4 100 102.1 100 89.4 100 98.7 100 95.1 100 96.9 100 93.3 100 100.5 100 .88.8 100 99.4 G§ - the control plants. T# - the treated plants. 28. T i l l e r i n g by treated plants did not d i f f e r greatly from the t i l l e r i n g by the controls. The r a t i o of treated to control varied from 92,1 s 100 to 102.4 : 100. Dry weights of the treated plants were decreased i n rough proportion to the degree of treatment within the experimental classes (a) producing v i s i b l e injury, and (b) producing no v i s i b l e injury. Plants with v i s i b l e injury to 30$ of the l e a f area produced a dry weight 82.7$ as heavy as that of the controls; while plants with injury to 5$ of the l e a f area produced dry weight 93.7$ as heavy as the controls. Plants with no v i s i b l e injury but exposed to 480 hours csf treatment with sulphur dioxide at a concentration of 0.27 p.p.m. produced a dry weight 93,2$ as heavy as that of the controls; while plants exposed to 51 hours of gas at a con- centration of 0.36 p.p.m. produced 99.9$ as much as the control dry weight. Transpiration differences were very noticeable between the control and treated plants i n each experiment. In order of experiment number, the r a t i o s of control transpiration c o e f f i c i e n t to those of the treated ares 100:65, 100:95, 100:80, 100:95. The difference i n transpiration c o e f f i c i e n t s of injured plants i s greater than the true transpiration difference, due to the reduction of transpiration surface through injury, nevertheless, a diminishment of the per unit surface transpiration d i d take place. This might be explained partly upon the basis of p a r t i a l closure of the stomata through some effect of the sulphur dioxide. Such an ef f e c t might be due to a change i n aci d i t y , held by Scarth (12) to be of great importance i n stomatal movement. Or the diminishment of transpiration might be explained by postulating a diminished r e s p i r a t i o n rate. According to evidence advanced by workers i n t h i s f i e l d , transpiration i s a process requiring a large expenditure of energy by the 29» plant, and consequently the rate of respiration may become a l i m i t i n g f a c t o r . These explanations would f u l l y account for the measured decreases i n transpiration recorded. Calcium, magnesium, and potassium content per unit dry weight were diminished i n a l l the treated plants excepting those i n experiment 2, where the treatment was of 12 hours duration only. This i s regarded as in d i c a t i n g a diminished absorption rate of these elements. The magnesium content i n the plants grown i n the greenhouse was about 0.8$, while i n the plants grown i n cabinets i t was about 0.6$. This difference might be correlated with the l i g h t -conditions and the l e a f fractions of the t o t a l green weights. Nitrogen (total) content was diminished appreciably i n the treatment where v i s i b l e injury to 30$ of the l e a f area was produced (H r a t i o was 100s95.3) and i n the treatment of 480 hours duration i n which no v i s i b l e injury was produced (N ratio, was 100:88.8). In the other two experiments there were no appreciable differences between control and treated plants. The nitrogen content was quite high i n a l l plants. Phosphorus was also f a i r l y high. The ra t i o s of P:N i n experiments number 1 and 3 are d i f f e r e n t . This might be regarded as an effect upon the phosphoproteins i n the growing parts of the plant; that i s , the amount of phosphorus was l e s s i n the plants which showed a diminished growth during the l a t e r stages. Sulphur content showed great variation i n the treated plants. Arranged i n order of experiment numbers, the r a t i o s of control to treated ares 100:'86.4, 100:95.8, 100:137.4, 100:102.1. Consideration of the treatments and the res u l t s of analyses suggests that the sulphate absorption by treated plants from the nutrient solution i s lowered, but 30. that treatment of s u f f i c i e n t duration w i l l increase the t o t a l sulphur. In experiment 3, the plants were treated for 480 hours; the sulphur content was increased 37.4$ for the whole plant. Ash analyses include s i l i c o n traces which cannot be excluded i n culture work of t h i s kind. The ash for a l l experiments, excepting . number 3, was lower i n the treated, plants than i n the control plants. Ratios of control to treated plants are 100:95.7, 100:98.9, 100:100.3, 100:95.5. This agrees, i n general, with the r e s u l t s found i n separate a n a l y t i c a l procedures. The s l i g h t l y higher ash found i n the treated plants of experiment number 3 i s evidently the r e s u l t of the high sulfur content of the treated plants. Absorption i s regarded as a physiological function independent of transpiration. At the present time both functions can only be ex- plained by postulating expenditure of energy by the plant to maintain them. Other researches seem to establish t h i s f a c t . In these experiments a lowered transpiration was recorded and a lowered absorption of inorganic nutrients per gram dry weight was measured (assuming analyses to indicate the absorption) i n treated plants as compared to control plants. This can be explained on the hypothesis that sulphur dioxide lowers the r e s p i r a t i o n rate of the plant without affecting the rate of photosynthesis i n the same degree. No d i r e c t texperimental evidence i s advanced to substantiate t h i s explanation. SUMMARY: Four experiments upon barley plants have been conducted under described environmental conditions. These experiments consisted of treatments with sulphur dioxide i n a range of low concentrations with 31. averages from 0.27 p.p.m. to 0.40 p.p.m. The duration of exposure i n the treatments varied from 6 to 480 hours; and the range of humidity between experiments was from 40$ r e l a t i v e humidity to 100$. V i s i b l e injury was only produced when the r e l a t i v e humidity was extremely high and the extent was influenced by the duration of ex- posure as well as the concentration of the gas. No v i s i b l e injury was produced i n medium and f a i r l y low humidities by lengthy, treatments of sulphur dioxide at the same concentrations. T i l l e r i n g by the plants was not appreciably altered by treatments. The y i e l d , as measured by dry weights, was reduced i n three experiments. The reduction i n y i e l d could be considered as roughly proportional to the severity of the treatment (a) producing v i s i b l e injury to the plants and (b) producing no v i s i b l e injury to the plants. Transpiration by the plants was measured. In each experiment transpiration by the treated plants was decreased. Transpiration c o e f f i c i e n t s have been calculated. The dry material was analyzed by recognized quantitative methods for the following elements; calcium, magnesium, potassium (including sodium trace), sulfu r , phosphorus, and nitrogen ( t o t a l ) ; and an ash determination was made. The results showed a decrease i n the concentration of these elements per unit dry weight i n the more severe treatments. Sulfur was higher i n the experiments of long duration. Consideration of the r e s u l t s lead to the conclusion that absorption of inorganic nutrients from solution i s decreased by treatment with sulphur dioxide. Transpiration and absorption are now regarded as plant functions requiring an energy expenditure by the plant. The decrease i n transpiration and absorption of inorganic nutrients may be explained i f the sulphur dioxide i s assumed to decrease the r e s p i r a t i o n rate of the plant without 32. the same relative decrease i n the rate of photosynthesis. •55. VI For constant d i r e c t i o n and aid i n t h i s study, and f o r generous provision of laboratory f a c i l i t i e s , the writer wishes to express his sincere appreciation to Dr. A.H. Hutchinson of the University. To Dr. Morris Katz of the National Research Council thanks are also due for suggesting t h i s study, and for helping i n several problems involved. The suggestions made by Dr. F. Dickson and Dr. H. Harris have been of great value i n treating the data. This study would not have been possible without the aid of grants for equipment from the National Research Council, Ottawa, and from the University of B r i t i s h Columbia. VII Bibliography, Holmes, J.A,, Franklin, E.C„, and Gould, R.A. Report of the Selby Smelter Commission, U.S. Bureau of Mines, B u l l e t i n 98, (528 pp.), Washington, D.C., 1915, Benton, A.F, Gas flow meters f o r small rates of flow, Ind. & Eng. Chem., 2, pp. 62S-629, 1919, Thomas, M,D», and Abersold, J.N, Automatic apparatus for the determination of small concentrations of sulfur dioxide i n the a i r . Ind, & Eng. Chem,, Anal. Ed. 1, 14, 1929. G r i f f i n , S.W., and Skinner, W'.W. Small amounts of sulfur dioxide i n the atmosphere. I. Improved method for determination of SOg when present i n low concentration i n a i r . Ind, & Eng. Chem., 24, 1932. Davis, A.R., and Hoagland, D.R. An apparatus for the growth of plants i n a controlled environment. Plant Physiology, 3, pp. 277-292, 1928. Swain, R.E., and Johnson, A.B. E f f e c t of sulphur dioxide on wheat development. Action at low concentrations. Ind. & Eng. Chem., 28, pp. 42-47, 1936. Eaton, E.M. - • Automatically operated sand-culture equipment. Jour. Agr. Research, 53, pp. 433-444, 1936. Briggs, L.J. and Shantz, H.L. Relative Water Requirements of Plants. Jour. Agr. Research 3,, pp. 1-64, 1914, And subsequent publications. The Association of O f f i c i a l A gricultural Chemists. O f f i c i a l and Tentative Methods of Analysis, 4th edition, Washington, D.C., 1936. Ketz, Dr. M., and associates. Unpublished data. National Research Council, Canada. 56. 11. Jack, W.R. Unpublished data. 12. Scarth, G.W. _ Report to Ithaca Congress of Plant Science, 1926. Bot. Gaz., 82, p. 454, 1926. And subsequent publications.


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