Temperature effects on the response to sulphur of barley,peas and rape

Summary The effects of temperature and sulphur nutrition on the growth, yield and mineral composition (N, NO₃-N, S and SO₄-S) ofHordeum vulgare L. cv Olli,Pisum sativum L. cv Dark Skin Perfection, andBrassica campestris L. cv Arlo, were investigated in controlled environments. When barley and rape plants were grown at O ppm S, deficiency symptoms developed in about two weeks, whereas peas at the same level developed deficiency symptoms in about three weeks. The location of the deficiency symptoms varied between species. Plant weight increased with increasing S levels, but the shoot had a greater growth response than did the root. Optimum day/night growing temperature regimes for barley and peas were found to be near 24/16 at four weeks from seeding and near 18/10°C at the mature stage as evident from weights, maximum fruit set and mineral uptake. Optimum temperature for rape plants was near 29/21°C at both stages of growth. Mineral concentration was higher at four weeks after seeding than at the mature stage in pea and rape plants, while in barley the mineral concentration was similar at both stages of growth. With increase in S supply there was an increase in concentration of both total S and SO₄-S. Concentrations also increased with increasing temperatures. S deficient plants had increased total N and NO₃-N concentrations in all three species. NO₃-N concentration also increased with an increase in temperature while total N concentration was not appreciably influenced. These experiments indicated that the effects of S nutrition on growth, development and mineral composition of plants depends on the species, temperature regime and growth stage     

Effects of sulphur dioxide fumigation on soil system and growth behaviour ofVicia faba plants

Summary To determine the possible changes in soil characteristics and plant growth resulting from SO₂-exposure, field grownVicia faba plants were exposed to 0.5 ppm SO₂ for 4 h daily from 40 to 100 days of their ages. The major effects of SO₂ on soil system includes increases in contents of total sulphur, organic carbon and exchangeable Al; lowering of pH and decreases in contents of N, P and exchangeable K and Ca. Besides, SO₂ interfered with nutrient uptake and plant growth leading to reductions in lengths of root and shoot, numbers of leaves, nodules and pods, phytomass accumulation and net primary productivity.     

Responses of dry weight growth under SO2 stress in an SO2-tolerant plant,Polygonum cuspidatum

The effects of exposure to 0.5–0.7 ppm SO₂ for about one month on the dry weight growth and net photosynthesis ofPolygonum cuspidatum were investigate. Furthermore, the carbon and nitrogen concentrations in each plant organ were measured. The results obtained showed no significant decrease in the total dry weight of SO₂-treated plants in comparison with controls. On the other hand, the leaf area (LA) and/or leaf dry weight of SO₂-treated plants were increased, and the root dry weight (RW) was decreased, in comparison with controls. The leaf carbon assimilation rate (CAR) in SO₂-treated plants was slightly decreased in spite of a clear decrease in net photosynthesis, and the value of (SW+RW)/LA (SW stem dry weight) was decreased in comparison with controls, thus minimizing the reduction in CAR. Furthermore, the ratio of total leaf carbon absorption (leaf area x CAR) to total root nitrogen absorption (root dry weight x nitrogen assimilation rate) in SO₂-treated plants was similar to that in controls. From these results, it can be concluded that an increase in leaf area and/or leaf dry weight and a decrease in root dry weight inP. cuspidatum under SO₂ stress may be induced in order to compensate for the decrease in CAR and to maintain the ratio of total leaf carbon absorption to total root nitrogen absorption in the early stage of vegetative growth.     

Studies on sulphur in vertisols

Summary Some soil and plant test methods were evaluated for predicting response of soybean crop (Glycine max (L.) Merr.) to S application in vertisols. Morgan's reagent, 500 ppm P containing Ca(H₂PO₄)₂.H₂O and KH₂PO₄ solutions, 0.5N NH₄OAc+0.25N HOAc and 0.15% CaCl₂ were found to be suitable extractants for measuring available soil S. The critical limits of extractable S were 9.0 ppm by Morgan's reagent, 10.0 ppm by phosphate solutions, 8.0 ppm by 0.5N NH₄OAc +0.25N HOAc and 14.0 ppm by 0.15% CaCl₂. Morgan's reagent was regarded as superior to other soil test methods in view of its high relationship with S uptake by plants, A values and relative yield. Critical S concentration in soybean plants varied with age. It was 0.15% and 0.185% for 36 and 60 days old plants, respectively. The critical N/S ratio on the other hand appeared to be constant at about 16.5 during vegetative growth period. Constancy of critical N/S ratio in plants was attributed to the near constancy of N/S ratio in plant proteins. There was highly significant relationship between response of soybean to S and to N, supporting the conclusion of some earlier workers that any soil showing large responses to N may not be supplying adequate S from the mineralization of soil organic matter.     

Performance of chickpea,lentil and lupin nodulated with indigenous or inoculated rhizobia micropartners under nitrogen,boron, cobalt and molybdenum fertilization schedules

Chickpea (Cicer arietinum), lentil (Lens esculenta) and lupin (Lupinus albus) responded to inoculation with their respective symbiotants:Rhizobium loti, Rhizobium leguminosarum biovarviceae andBradyrhizobium sp. (Lupinus) alone or with (NH₄)₂SO₄ at 30 ppm N. Soil application of Na₂MoO₄.2H₂O at 3 ppm Mo, CoCl₂.6H₂O at 2 ppm Co²⁺ or Na₂B₄O₇.10H₂O at 1 ppm B with 0 and 30 ppm N increased nodule weight and plant dry weight and N-content 60 days after sowing and seed yield, seed size and the N and P contents of seed. Nodule numbers slightly decreased with application of such chemicals. Mo enhanced performance of the three plants more than Co and B. Yield, total N and P-contents of lupin were comparable with those of chickpea or lentil and lupin had the highest levels of both N₂-fixation and N absorption from the fertilizer. IndigenousR. leguminosarum biovarviceae was more established in the soil compared with the other two, chickpea and lupin, micropartners.     

The influence of sublethal concentrations of sulfur dioxide on morphology,growth and product yield of the duckweed Lemna minor L.

Summary There was no disturbance in the growth of Lemna minor L. with a SO₂ concentration of up to 0.3 ppm in air. A SO₂ concentration of 0.6 ppm caused an initial depression of the growth rate of about 25%, but in the course of adaptation, the rate rose to the values of the control. The average dry weight per frond was not influenced by the SO₂ fumigation. The initial sporadic appearance of chloroses by fumigation with 0.6 ppm SO₂ was considered a sign of the proximate toxicity limit for Lemna minor L. With 0.15 ppm SO₂ in air, the size of the fronds was reduced. The average surface of the fronds was diminished by 0.3 ppm SO₂ for about 16% as compared with the control plants.The protein remained quantitatively uneffected up to a SO₂ concentration of 0.6 ppm. As a qualitative influence of SO₂, the nitrogen content of the proteins remained constant, but the sulfur content of the proteins increased.Under 0.3 and 0.6 ppm SO₂, the starch content decreased immediately by 20–30%, under 0.15 ppm SO₂ the decrease reached the same level after a longer time than in the case of the higher concentrations.The SO₂ concentrations up to 0.6 ppm had no effect on chlorophyll concentration.The contents of C, N, H, P, K, Na, Ca, Mg, Mn, and Fe were not effected by SO₂ fumigation.Conclusion: SO₂ may have some effects on product yield, even under low concentrations, without provoking acute damage; the plant is able to adapt by regulation of its metabolism, and enters a new steady state.The study was supported by a grant of the Swiss National Science Foundation (project number 3.866.71)     

Litterfall and nutrient returns in red alder stands in western Washington

Summary Litterfall was collected over 1 year from eight natural stands of red alder growing on different sites in western Washington. The stands occurred at various elevations and on different soils, and differed in age, basal area, and site index. Most litterfall was leaf litter (average 86 percent). Amounts of litterfall and leaf litter varied significantly (P<0.05) among the sites. Average weights of litterfall and leaf litter in kg ha^–1 yr^–1, were 5150 and 4440, respectively. Weight of leaf litter was not significantly (P<0.05) related to site index, stand age, or basal area. The sites varied significantly (P<0.05) in concentrations of all elements determined in the leaf litter, except Zn. Average chemical concentrations were: N, 1.98 percent; P, 0.09 percent; K, 0.44 percent; Ca, 1.01 percent; Mg, 0.21 percent; S, 0.17 percent; SO₄–S, nil; Fe, 324 ppm; Mn, 311 ppm; Zn, 53 ppm; Cu, 13 ppm; and Al, 281 ppm. There were significant correlations between some stand characteristics and concentrations of some elements, and among the different chemical components of the leaf litter. Important correlations were found between stand age and P concentration (r=–0.84,P<0.01); weight of leaf litter and P concentration (r=0.74,P<0.05); weight of leaf litter and K concentration (r=0.71,P<0.05); concentrations of N and S (r=0.81,P<0.05); and concentrations of Fe and Al (r=0.98,P<0.01). Returns of the different elements to the soil by leaf litter varied among the different sites. Average nutrient and Al returns, in kg ha^–1 yr^–1, were: N, 82; Ca, 41; K, 19; Mg, 8; S, 7; P, 4; Fe, 1; Mn, 1; Al, 1; Zn, 0.2, and Cu, <0.1.     

Effect of zinc sources and levels on the growth and Zn nutrition of soybean (Glycine max. L.) in the presence of chloride and sulphate salinity

A study was conducted in a screen house in pots on a sandy loam soil deficient in Zn. Salinity was induced by adding 44, 88 and 132 me/l of chloride and sulphate salts in the saturation extract. To these treatments, 0, 5 and 10 ppm Zn were added as ZnSO₄·7H₂O or Zn-EDTA. The results indicated that the yield of soybean shoot was lowest at the highest salinity level and highest at the lowest level. Shoot yield improved markedly with Zn application. Both sources of Zn were equally effective in augmenting crop yields. Yields were low in Cl-salinity when compared with equivalent levels of SO₄-salinity. Application of ZnSO₄·7H₂O produced higher yields in SO₄-dominant salinity. Zinc content increased and Zn uptake decreased with increase in Cl-salinity regardless of Zn sources. In SO₄-salinity, ZnSO₄·7H₂O did not influence the Zn content, but uptake was suppressed with increase in SO₄-salinity. Increasing rates of SO₄-salinity enhanced Zn content in the presence of Zn-EDTA.     

Multiple stress and growth of barley: Effect of salinity and temperature shock

The effect of preconditioning to NaCl salinity (0 to 135 mmol L^-1) on the subsequent response of barley (Hordeum vulgare L.) to two days of low (5°C) temperature shock (LTS) was investigated. Both salinity and LTS reduced the final growth of barley tops and roots. The effect of LTS on growth of tops and roots depended on the level of salinity stress imposed. At salinity level of 45 mmol L^-1, for example, exposing the plants to LTS reduced top growth by an additional 34%; at 135 mmol L^-1 salinity, however, LTS reduced the top growth by only 2%. Salinity increased the concentration of Na, Cl, total P, PO₄, and Zn, reduced the concentration of K, Ca, total N, NO₃, and SO₄, but did not affect the concentration of total S in the barley tops. LTS increased the concentration of Ca and Zn in the tops; the concentrations of other elements (cations and anions) were not changed by the temperature treatment. In the tops of the control plants, NO₃, PO₄, and SO₄ accounted for 15%, 72% and 93% of the total N, P, and S, respectively. In the plants grown at 135 mmol L^-1 NaCl, however, the above values were 8%, 84%, and 70%, respectively, which indicates that salinity had altered the incorporation of N, P, and S into organic compounds. We suggest that salinity and low temperature affect growth and nutrient uptake and incorporation into organic matter by different mechanisms. Although barley subjected to low salinity becomes more sensitive to subsequent low temperature stress, preconditioning of barley to higher salinity stress seems to reduce the plant's sensitivity to subsequent low temperature.     

Influence of anions on the potassium status and productivity of kiwifruit (Actinidia deliciosa) vines

The effects of K fertiliser (160 kg ha^-1) applied with Cl^- or SO₄ ^2- as the accompanying anion on the K nutrition of kiwifruit (Actinidia deliciosa var. deliciosa) were assessed in a field experiment, using vines with varying degrees of K deficiency. Leaf K concentrations in spring were significantly higher for vines receiving KCl, compared to those receiving K₂SO₄. This effect did not interact significantly with the degree of K deficiency, and persisted for about 6 weeks. Subsequently there was no significant difference between the leaf K concentrations for the vines receiving KCl or K₂SO₄. Applying K as KCl increased the leaf Cl concentration, especially in spring, while applying K as K₂SO₄ had no significant effect on the leaf S concentration at that time. These results implied a greater requirement for organic acid anions for K⁺ uptake from K₂SO₄ than from KCl, and the importance of organic acid anions for K⁺ uptake from different sources of K fertiliser is discussed. This transient effect of the accompanying anion on leaf K status was associated with large effects on flowering, and fruit yields were about 28% higher for plants receiving KCl rather than K₂SO₄.The effects on growth and tissue nutrient composition of varying the concentrations of Cl^-, NO₃ ^-, SO₄ ^2- and H₂PO₄ ^- around the roots of kiwifruit vines were examined in a solution culture experiment. For H₂PO₄ ^-, plant growth was very similar over a wide range of rates of addition. For the other anions, the range between deficiency and toxicity was clearly delineated. For Cl^- and NO₃ ^-, toxicity was associated with high tissue concentrations of Cl and N, respectively, and was consistent with competition for uptake between Cl^- and NO₃ ^-. However, for SO₄ ^2-, toxicity was associated with only a small increase in the tissue S concentration relative to that associated with maximum growth, and appeared to result more from effects on uptake of other anions and cations rather than from direct effects of high tissue S concentrations.It is concluded that the sensitivity of kiwifruit to the anion accompanying K⁺ in fertiliser may be related to the unusually high requirement for Cl previously reported for this species.     

Response of barley and wheat to phosphorus in the presence of chloride and sulphate salinity

Summary The study was conducted in a greenhouse and under field conditions. In the greenoouse, barley was grown to maturity in pots on a sandy soil which contained 80 and 120 meq/l of chloride and sulphate dominant salts in its saturation extract, to which 0, 10, 25 and 50 ppm P were added. In the field study, wheat was grown on loamy sand soils having 0, 25, 50 and 75 kg/ha added P levels and irrigated with either Cl- or SO₄-dominant saline waters (EC=15–19 mmhos/cm). The results of the greenhouse study indicated that at maturity barley straw and grain yield was significantly increased by 50 ppm of added P both on the non-saline control and the Cl-treatments. However, 25 ppm P was optimal on the SO₄-treatments. The Cl content of plants was significantly decreased and S was increased with the increase in the P content of soil. A synergistic relation between the S and P content of barley shoots was observed. In the field study wheat grain yield responded significantly to P applications upto 50 kg/ha level on the Cl-site and there was no response to applied P on the SO₄-site, although the former contained more Olsen's P than the latter. The results suggested that P requirement of wheat and barley was greater on Cl- than on SO₄-salinity.     

Differential Na2SO4 tolerance in tobacco plants regenerated from Na2SO4-grown callus

Abstract The regenerated shoots from sodium sulphate (Na₂SO₄) grown callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) were evaluated for Na₂SO₄ tolerance based on shoot proliferation and rooting in vitro, and seed germination in vivo in response to Na₂SO₄. An increase in Na₂SO₄ concentration resulted in significantly decreasing shoot fresh weight, number of shoots, shoot length and leaf size, and increasing per cent shoot dry weight of both control and Na₂SO₄-grown cultures. In rooting, shoots of Na₂SO₄-grown cultures exhibited the highest per cent rooting (85%) in the presence of 1% w/v Na₂SO₄. However, per cent rooting, root number per rooted cutting and root fresh weight decreased significantly with increasing Na₂SO₄ concentration when shoots were transferred to the medium in the absence of Na₂SO₄ for 4-monthly passages. Following acclimatization of the rooted shoots of Na₂SO₄-grown cultures, phenotypic variation was observed during growth and development. There were 13.2% sterile plants. Fertile plants were sorted into normal (N), tolerant (T), and sensitive (S) categories and the respective percentages of plants were 31.6, 44.7 and 10.5, based on per cent germination, germination velocity index and seedling survival to Na₂SO₄. The response of N, T and S types to Na₂SO₄ in subsequent shoot proliferation was similar to that of seed germination.     

Effects of sulfur deficiency on non-protein nitrogen,soluble sugars,and N/S ratios in young corn (Zea mays L.) plants

Summary The concentrations of several N fractions, soluble sugars and N/S ratios were determined in Golden Bantam sweet corn and hybrid field corn grown in nutrient solutions and/or soil with various SO₄-S levels provided. When the level of SO₄-S supplied was less than that needed for maximum growth, higher-than-normal concentrations of amide (asparagine) N and lower-than-normal soluble sugar concentrations were found in the plants. An inadequate S supply appears to limit the plants capacity to synthesize protein to a much greater extent than it inhibits the nitrogen uptake mechanism.Total N/total S ratios (grammole basis) varying from over 100 to less than 15 were found in plants grown with different levels of sulfate supplied. When SO₄-N, NO₃-N, and the large amount of amide-N which accumulates under conditions of S deficiency are excluded, the ratio in young corn plants is generally between 22–50. The precision of the N/S ratio as an indicator of S adequacy for growing crops might be improved by a better understanding of the nature of the forms in which N and S occur in plants, and the effects of soil and plant factors other than S level. The percentage of amide-N shows promise as an indicator of S nutrient status. Data available indicates that added S will increase yields of corn plants if their amide-N level exceeds 500 ppm. Amide-N concentration correlates with N/S ratios, and it is much more readily determined than the latter. Its usefulness as a S nutrition indicator should be checked under field conditions.     

Evaluation of chemical methods for estimating available zinc and response of green gram (Phaseolus aureus roxb) to applied zinc in non-calcareous soils

Summary Studies were conducted in 22 non-calcareous soils (India) to evaluate various extractants,viz. (6N HCl, 0.1N HCl, EDTA (NH₄)₂CO₃, EDTA NH₄OAc, DTPA+CaCl₂ and 1M MgCl₂) to find critical levels of soil and plant Zn for green gram (Phaseolus aureus Roxb.). The order of extractability by the different extractants was 6N HCl>0.1N HCl>EDTA (NH₄)₂CO₃<EDTA NH₄OAc DTPA+CaCl₂>1M MgCl₂. Critical levels of 0.48 ppm DTPA × CaCl₂ extractable Zn, 0.80 ppm EDTA NH₄OAc extractable Zn, 0.70 ppm EDTA (NH₄)₂CO₃ extractable Zn, and 2.2 ppm 0.1N HCl extractable Zn were estimated for the soils tested. The critical Zn concentration in 6 weeks old plants was found to be 19 ppm. The 0.1N HCl method gave the best correlation (r=0.588^**) between extractable Zn and Bray's per cent yield, while with DTPA+CaCl₂, it was slightly low (r=0.542^**). The DTPA + CaCl₂ method gave significant (r=0.73^**) correlation with plant Zn concentration. The 0.1N HCl gave the higher correlation with Zn uptake (r=0.661^**) than DTPA (r=0.634^**) 6N HCl and 1M MgCl₂ method gave nonsignificant positive relationship with Bray's per cent yield. For noncalcareous soils apart from the common use of DTPA+CaCl₂, 0.1N HCl can also be used for predicting soil available Zn. The use of 0.1N HCl would be much cheaper than DTPA and other extractants used in the study.     

Photosynthetic and growth response to fumigation with SO2 at elevated CO2 for C3 and C4 plants

Summary Six early successional plant species with differing photosynthetic pathways (3 C₃ species and 3 C₄ species) were grown at either 300, 600, or 1,200 ppm CO₂ and at either 0.0 or 0.25 ppm SO₂. Total plant growth increased with CO₂ concentration for the C₃ species and varied only slightly with CO₂ for the C₄ species. Fumigation with SO₂ caused reduced growth of the C₃ species at 300 ppm CO₂ but not at the higher concentrations of CO₂. Fumigation with SO₂ reduced growth of the C₄ species at high CO₂ and increased growth at 300 ppm CO₂. Leaf area increased with increasing CO₂ for all plant species. Fumigation with SO₂ reduced leaf area of C₃ plants more at low CO₂ than at high CO₂ while leaf area of C₄ plants was reduced more at high CO₂ than at low CO₂. These results support the notion that C₃ species are more sensitive to SO₂ fumigation than are C₄ species at concentrations of CO₂ equal to that found in normal ambient air. However, the difference in sensitivity to SO₂ between C₃ and C₄ species was found to be reversed at higher concentrations of CO₂. A possible explanation for this reversal based upon differences in stomatal response to elevated CO₂ between C₃ and C₄ species is discussed.     

Seasonal and SO2-induced changes in epicuticular wax of ryegrass

Epicuticular wax was extracted from SO₂-sensitive (S23) and SO₂-resistant (BR) genotypes of ryegrass (Lolium perenne) exposed continuously for 4 weeks to 0, 0.05 or 0.15 ppm SO₂ under winter or summer conditions. The differences found between genotypes in the composition of the acid and alkane fractions of the extracted wax were further modified by season and exposure to SO₂. Estimates of relative amounts of epicuticular wax showed that both genotypes produced more wax in the winter experiment, with BR producing more wax than S23. Exposure to 0.05 ppm in the winter experiment had little effect on the amount of wax produced by either genotype while exposure to 0.15 ppm SO₂ greatly reduced wax production in BR but increased wax production in S23. These changes in wax production could have been due to a general effect of SO₂ on metabolism regulating the flow of carbon into the pathways synthesizing wax components rather than to specific inhibition or enhancement at particular steps in these pathways. Exposure to SO₂ in the summer experiment had little effect on the amount of wax produced by both genotypes but did have an effect on wax composition.     

Interactive Effects of Sulphur Dioxide and Mineral Nutrient Supply on Photosynthetic Characteristics and Yield in Four Wheat Cultivars

Field experiments were conducted on four cultivars of wheat (Triticum aestivum L.) to examine the variability in cultivar response to sulphur dioxide (SO₂) under different concentrations of mineral nutrients. Thirty-days-old plants were exposed for 8 weeks to 390±20 µg m^–3 (0.15 ppm) SO₂ for 4 h per day, 5 d per week. Decline in net photosynthetic rate, contents of pigments and nitrogen, biomass and grain yield of each cultivars were due to SO₂ at all the nutrient concentrations studied. However, the magnitude of reduction was higher in plants grown without nutrient application. On the basis of the reductions in photosynthesis and yield, the susceptibility of wheat cultivars to SO₂ was in the order of Malviya 213 > Malviya 37 > Malviya 206 > Malviya 234 at recommended dose of NPK, whereas the same without the nutrients was Malviya 206 > Malviya 234 > Malviya 213 > Malviya 37.     

Macronutrient content in leaves of bean plants (Phaseolus vulgaris,L.) grown with differents rates of N/S as fertilizers

Summary The effect of increasing rates of nitrogen (N) and sulphur (S) as fertilizers on the yield, leaf area and N, P, S, Ca, Mg, NO₃ ⁻ and SO₄ ⁼ content in leaves of bean (Phaseolus vulgaris, L.) were studied in a hydroponic culture experiment under greenhouse conditions. Bean plants responded significantly to all treatments with differents N/S ratios. When plants grew with high N/S ratios, the leaf content of N, Ca and NO₃ ⁻ increased while the content of K, P and SO₄ ⁼ decreased. However, optimal yield and leaf area were not obtained. Optimal leaf and fruit dry matter was obtained at N/S ratio value of 1.41. When lower N/S rates were used, optimal leaf and fruit dry matter was only observed when the leaf N/S ratio was between 15 and 16. At high sulphate levels in the nutrient solution there is no interaction with nitrate which is easily observed, resulting in an increase in yield. An interaction between nitrate and sulphate in the nutrient solution was found at a N/S ratio of 0.81 which produced in leaves a synergic effect between P-K, an antagonistic effect between N-P and N-K and a lower yield. This research was supported by Fundacion ‘Ramon Areces’.     

Mechanism of nitrogen effect on zinc nutrition of flooded rice

Summary Nitrogen application increased Zn contents of flooded rice on two calcareous soils. Urea and (NH₄)₂SO₄ being better N carriers than NH₄NO₃ resulted in higher increase. Nitrogen enhanced Zn contents partly through growth promotion but mainly by increasing soil Zn solubility and root efficiency for Zn absorption. Zinc solubility rose by an enigmatic mechanism and not from pH reduction or soluble Zn-HN₃ complex formation as occurs for upland plants. Nitrogen aggravated Zn retention in upland plant roots as immobile Zn-protein complex was not important for rice. Bicarbonate inhibition of Zn uptake by rice from CO(NH₂)₂ application or its stimulation by lower redox potential from NH₄NO₃ addition were not involved.No. V in the series Micronutrient availability to cereals from calcareous soils.     

Ecology of SO2 resistance: I. Effects of fumigations on gas exchange of deciduous and evergreen shrubs

Summary A unique gas exchange system is described in which photosynthesis, transpiration, and stomatal conductance can be measured on leaves during SO₂ fumigations. SO₂ concentrations can be continuously monitored and manipulated between 0 and 2.0 ppm. Rates of total SO₂ uptake and SO₂ absorption through stomates of a fumigated leaf can also be determined.Using this system we compared the effects of SO₂ on the gas exchange rates of two shrub species that co-occur in the Califormian chaparral. Diplacus aurantiacus, a deciduous shrub, was more sensitive to SO₂ fumigation than Heteromeles arbutifolia, an evergreen shrub. The differences in photosynthetic sensitivity could be attributed, in large part, to differential SO₂ absorption rates.