Seasonal variations in apparent photosynthesis among plant stands of different soybean cultivars

The CO₂- and H₂O-exchange rates between soybean canopies and the atmosphere were measured in three mobile chambers (4 m³). Each chamber stopped at 8 or 9 plots (3.1-m² ground area) every 25 min. Diurnal and seasonal CO₂-exchange rates (CER) of 13 soybean (Glycine max (L.) Merr.) cultivars are summarized here. The oldest two cultivars, released in 1927 and 1932, had the lowest CER values. The CER usually decreased in the afternoon (23.4 vs 27.8 mol CO₂ m^-2 s^-1 at 1.6 mmol photons m^-2 s^-1), except shortly after rainfall. During a drought, these reductions occurred earlier in the day and were more pronounced. We present evidence for a nonstomatal component of the CO₂ flux-reaction system causing CER reductions during a water stress. Daytime CER values were not correlated with temperature (24–34° C), but nighttime values were (15–25° C, r=0.85,* n=41).     

Nonstructural carbohydrates of soybean plants grown in subambient and superambient levels of CO2

Photosynthesis Research - Elevated carbon dioxide (CO2) concentration increases plant photosynthesis, biomass and carbohydrate accumulation. Since plants have grown in low CO2 (200 to 300 µmol...     

Physiological comparisons of two soybean cultivars differing in canopy photosynthesis. I. Variation in vertical 14CO2 labelling and dry weight partitioning

Differences in canopy apparent photosynthesis (CAP) among soybean [Glycine max (L.) Merr.] genotypes have been shown to be correlated to seed yields. Since the physiological basis for such differences in CAP is unknown, two cultivars known to differ in CAP, Tracy and Davis, were studied during the 1978–1980 growing seasons. The CAP and dry weights of component plant parts were determined. In 1978 and 1979, ¹⁴CO₂ uptake by vertical leaf strata was determined and specific leaf weight (SLW) and leaf area index (LAI) were determined for corresponding strata in 1979 and 1980. Measurements were taken on several dates during reproductive growth. With the exception of CAP, all measurements (¹⁴C uptake, dry weights) were made in layers within the canopy. CAP on some dates were significantly higher in Tracy than in Davis and integrated CAP values from a certain growth period, labeled as R5 to R7, averaged 16 percent higher in Tracy for the three years studied. No differences in the relative recovery of ¹⁴C from different layers of leaves in the canopy were found. This indicates that variations in canopy structure or leaf orientation did not play a major role in the CAP differences between cultivars. The differences seem related to variations in leaf dry weights. Overall, Tracy exhibited 13.5, 19.2, and 13.2 percent greater leaf dry weights than Davis during 1978, 1979, and 1980, respectively. These differences in leaf dry weight seem largely due to a differences in the SLW. Data from these experiments indicate that differences in soybean CAP values were associated with differences in SLW.Abbreviations CAP Canopy Apparent Photosynthesis - CER Carbondioxide Exchange Rates - EST Eastern Standard Time - LAI Leaf Area Index - LSD Least Significant Difference - POPOP 1,4-bis-[2(5-phenyloxazdyl)]-benzene - PPO 2,5-diphenyloxazole - SLW Specific Leaf Weight     

Interactive effects of light,leaf temperature,CO2 and O2 on photosynthesis in soybean

A biochemical model of C ₃photosynthesis has been developed by G.D. Farquhar et al. (1980, Planta 149, 78–90) based on Michaelis-Menten kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase-oxygenase, with a potential RuBP limitation imposed via the Calvin cycle and rates of electron transport. The model presented here is slightly modified so that parameters may be estimated from whole-leaf gas-exchange measurements. Carbon-dioxide response curves of net photosynthesis obtained using soybean plants (Glycine max (L.) Merr.) at four partial pressures of oxygen and five leaf temperatures are presented, and a method for estimating the kinetic parameters of RuBP carboxylase-oxygenase, as manifested in vivo, is discussed. The kinetic parameters so obtained compare well with kinetic parameters obtained in vitro, and the model fits to the measured data give r ²values ranging from 0.87 to 0.98. In addition, equations developed by J.D. Tenhunen et al. (1976, Oecologia 26, 89–100, 101–109) to describe the light and temperature responses of measured CO₂-saturated photosynthetic rates are applied to data collected on soybean. Combining these equations with those describing the kinetics of RuBP carboxylase-oxygenase allows one to model successfully the interactive effects of incident irradiance, leaf temperature, CO₂ and O₂ on whole-leaf photosynthesis. This analytical model may become a useful tool for plant ecologists interested in comparing photosynthetic responses of different C₃ plants or of a single species grown in contrasting environments.Abbreviations PCO photorespiratory carbon oxidation - PCR photosynthetic carbon reduction - PPFD photosynthetic photon-flux density - RuBP ribulose bisphosphate     

Correlations among leaf CO2-exchange rates,areas and enzyme activities among soybean cultivars

Soybean (Glycine max (L.) Merr.) genotypes varying in area per nodal unit (usually a trifoliolate) and maturity class were grown in plots at the University of Illinois experimental farm. Leaf CO₂-exchange rates per unit area (CER) were measured under sunlight on intact plants. In addition to previously reported correlations with specific leaf weight and chlorophyll, CER was positively correlated with ribulose bisphosphate carboxylase (RuBPcase) activity, specific activity, and soluble protein, and was negatively correlated with area per leaf unit. The CER: chlorophyll correlation was destroyed by high CER values in 2 chlorophyll-deficient lines. CER values for 27 of the 35 lines tested fell within the range of those for isolines of cultivar Clark varying in leaf characteristics. The CER values were highest for fully expanded leaves during rapid pod fill. These results suggested that photoperiod (maturity) genes and genes for leaf area growth interact with genes controlling photosynthetic CO₂-exchange to produce the major differences in CER values among soybean genotypes.     

Soybean leaf photosynthesis in relation to maturity classification and stage of growth

Leaf photosynthetic rates were measured on field-grown soybeans during the 1980 season. Comparisons were made between different cultivars and isolines representative of maturity groups I–IV. Mature, fully expanded leaves at different nodes on the plant were measured in high light to determine which had the highest potential photosynthetic rates at any one time. Successive leaves during the growing season had maximum rates which increased from about 22 mol CO₂ m^-2 s^-1 on 25 June to a peak of 30–44 mol CO₂ m^-2 s^-1 in early August.The persistency and eventual decline in the maximum rate was associated with the maturity group and related dates of flowering, pod fill and onset of senescence. Early maturing cultivars (groups I and II) had higher peak rates (38–44 mol CO₂ m^-2 s^-1) than later maturing cultivars (30–35 mol CO₂ m^-2 s^-1, groups III and IV). However, the photosynthetic rates of early maturing cultivars declined rapidly after attaining their peak, whereas the leaves of later maturing cultivars maintained their photosynthetic activity for much longer.     

Physiological comparisons of two soybean cultivars differing in canopy photosynthesis. II. Variation in specific leaf weight,nitrogen, and protein components

Cultivar differences in canopy apparent photosynthesis (CAP) have been observed in soybean (Glycine max (L.) Merr.) but little is known about the physiological mechanisms which are responsible for such differences. This study was initiated to determine if variation in ribulose 1,5-bisphosphate carboxylase (RuBPCase) and soluble protein exists among cultivars which differ in CAP during reproductive growth. In addition, the relationship between specific leaf weight (SLW) and leaf protein was examined. Two Maturity Group VI cultivars, Tracy (high CAP) and Davis (low CAP), were grown in the field during 1979, 1980, and 1981 and in a greenhouse experiment. Leaves located at two canopy positions (topmost, fully expanded leaf and eighth node from the top) in 1979 and three canopy positions (those mentioned, plus the fourth node from the top) in 1980 and 1981 were sampled. Leaves at the two upper canopy positions exhibited greater SLW, RuBPCase m^–2, and soluble protein m^–2 than found at the eighth node down. Photosynthetic capacity of leaves at inner canopy regions was therefore affected by both light penetration into the canopy and leaf protein status. Over the three year period, the SLW was 23 percent and the soluble protein m^–2 leaf 21 percent greater in Tracy than in Davis. Although the trend in RuBPCase m^–2 leaf was not significant, it was consistently greater in Tracy in the field and greenhouse. No cultivar differences were observed when the proteins were expressed on a unit of leaf dry weight. The quantity of RuBPCase per unit leaf area was positively correlated with SLW with significant partial correlation coefficients of 0.62, 0.67, 0.35, and 0.82 for 1979, 1980, 1981, and the greenhouse study, respectively. Since these cultivars have similar leaf area indices during September, the greater SLW of Tracy is translated into more photosynthetic proteins per unit ground area and higher CAP rate.Abbreviations AP Leaf Apparent Photosynthesis - CAP Canopy Apparent Photosynthesis - DAP Days After Planting - DTT Dithothreitol - HEPES N-2-hydroethylpiperazine N-2 ethanesulfonic acid - LAI Leaf Area Index - LSD Least Significant Difference - PPFD Photosynthetic Photon Flux Density - PVP-40 Polyvinylpolypyrroledone (molecular weight, 4000) - RuBPCase Ribulose 1,5-bisphosphate Carboxylase - SLW Specific Leaf Weight     

Stomatal numbers of soybean and response to water stress

The relationship among stomatal density, photosynthetic rate, leaf conductance, plant growth, bean yield and kaempferol triglucoside (K9) in the leaves of soybean (Glycine max (L.) Merr.) was examined in two field tests. K9 in the leaves was associated with reduced stomatal density, reduced photosynthetic rate, reduced stomatal conductance, reduced plant weight and lower bean yield. Plants with high stomatal frequency (lacking K9) were better able to take advantage of increased water supply by increasing stomatal conductance (upper surface), transpiration and bean yield. Plants with low stomatal frequency (with K9) were unresponsive to irrigation and in this sense were more tolerant of water stress, but their overall yield was low.     

Photosynthesis at ambient and elevated humidity over a growing season in soybean

Daytime rates of net photosynthesis of upper canopy leaflets of soybeans were compared on 17 days for leaflets exposed to air at the ambient humidity and at a higher humidity. Leaflets at the higher humidity had higher rates of net photosynthesis on 16 of the 17 days. The daily total of net photosynthesis of leaflets at the higher humidity was on average 1.32 times that for leaflets at ambient humidity. A strong limitation of net photosynthesis by ambient humidity was found throughout the growing season.     

Separately and simultaneously induced dark chilling and drought stress effects on photosynthesis, proline accumulation and antioxidant metabolism in soybean

The effects of separately or simultaneously induced dark chilling and drought stress were evaluated in two Glycine max (L.) Merrill cultivars. For the separately induced dark chilling treatment (C), plants were incubated at 8 °C during 9 consecutive dark periods. During the days, plants were kept at normal growth temperatures. For the separately induced drought treatment (D), plants were maintained at normal growth temperatures without irrigation. For the simultaneously induced dark chilling and drought stress treatment (CD), plants were dark chilled without irrigation. All treatments caused similar decreases in pre-dawn leaf water potential, but resulted in distinct physiological and biochemical effects on photosynthesis. In Maple Arrow, where C had the smallest effect on photosynthesis, prolonged CD caused less inhibition of photosynthesis compared to D. Compared to Fiskeby V, the photosynthetic apparatus of Maple Arrow appears to possess superior dark chilling tolerance, a property which probably also conveyed enhanced protection against CD. Proline accumulation was prevented by CD at the ψ_PD where D already resulted in considerable accumulation. The superior capacity for proline accumulation in Maple Arrow would seem to be an important factor in its stress tolerance. Antioxidant activity evoked by CD and D was higher than for C alone. In Fiskeby V, the small increase in ascorbate peroxidase (EC 1.11.1.7) activity, which was in most cases not accompanied by increased gluthatione reductase (EC 1.6.4.2) activity, could impact negatively on its stress tolerance. These results demonstrate large genotypic differences in response to chilling and drought stress, even between soybean cultivars regarded as chilling tolerant.     

An evaluation of light and CO2 limitation of leaf photosynthesis by CO2 gas-exchange analysis

Numerical values which define the relative limitation of photosynthesis by light and CO₂ were computed from the slopes of light-and CO₂-response curves of photosynthesis. This method offers an easy approach for the characterization of photosynthesis of leaves.     

Nitrogen and carbon partitioning in soybean under variable nitrogen supplies and acclimation to the prolonged action of elevated CO2

This study was conducted to determine reciprocal effects of low to high doses of nitrogenous fertilizer (N₃₀, N₄₀, N₅₀, N₆₀ and N₇₀ — 30, 40, 50, 60 and 70 kg ha⁻¹ respectively) and CO₂ enriched environment on C and N partitioning in soybean (Glycine max (L.) Merril cv JS-335). Plants were grown from seedling emergence to maturity inside open top chambers under ambient, AC (350±50 mol mol⁻¹) and elevated, EC (600±50 mol mol⁻¹) CO₂ and analyzed at seedling, vegetative, flowering, pod setting and maturity stages. Soybean responded to both CO₂ enrichment and N supply. Leaves, stem and root reserves at different growth stages were analyzed for total C and N contents. Consistent increase in the C contents of the leaf, stem and root was observed under EC than in AC. N contents in the different plant parts were found to be decreased under EC-grown plants specially at seedling and vegetative stage despite providing N doses to the soil. Significant increase observed for C to N dry mass ratio under EC in the root, stems and leaves at seedling and vegetative stage was decreased in the middle and later growth stages possibly due to combined impact of N doses to the soil and increased N₂ fixing activities due to EC conditions. Critical analysis of our findings reveals that the composition and partitioning of C and N of soybean under variable rates of N supply and CO₂ enrichment alter according to need under altered metabolic process. These changes eventually may lead to alteration in uptake of not only N but other essential nutrients also under changing atmosphere.     

Net CO2 assimilation of taro and cocoyam as affected by shading and leaf age

Taro and cocoyam were grown outdoors in either full sun or under 40% shade. Leaves were tagged as they emerged and the effect of leaf age on net CO₂ assimilation rate (A) was determined. The effects of shading on A, transpiration (E), stomatal conductance for CO₂ (g_c) and H₂O (g_s), and water use efficiency (WUE) were also determined for leaves of a single age for each species. The effect of leaf age on A was similar for both species. Net CO₂ assimilation rates increased as leaf age increased up to 28 days with the exception of a sharp decline in A for 21 day-old leaves which corresponded to unusually low temperatures during the period of leaf expansion. A generally decreased as leaves aged beyond 28 days. Cocoyam had higher A rates than taro. Leaves of shade-grown plants had higher rates of A and E for both species at photosynthetic photon flux densities (PPFD) up to 1600 mol s^–1 m^–2. Shade-grown leaves of cocoyam had greater leaf dry weights per area (LW/A) and a trend toward higher g_c and g_s than sun-grown leaves. Shade leaves of taro had greater g_c and g₃ rates than sun-grown leaves. The data suggest that taro and cocoyam are highly adapted to moderate shade conditions.     

Effects of ambient UV-B radiation on soybean crops: Impact on leaf herbivory by Anticarsia gemmatalis

Replicated field experiments with large plastic filters were carried outin Buenos Aires (Argentina, 34° S) to study the impacts of current levelsofsolar UV-B radiation ( 315 ) on soybean(Glycine max L.) crops and their interactions with chewinginsects, in particular the soybean worm Anticarsiagemmatalis Hübner (Lepidoptera: Noctuidae). Solar(near-ambient)UV-B induced changes in the leaves that reduced their attractiveness toA. gemmatalis larvae in laboratory choicebioassays. When the A. gemmatalis larvae were forced toconsume leaves from field plots that received solar UV-B, they grew slightlyless rapidly and suffered more mortality than their counterparts fed withleavesfrom plots covered with polyester films that excluded the UV-B component ofsunlight. Exposure of the larvae themselves to ambient UV-B under a soybeancanopy during the feeding trials did not lower their life expectancy. At thewhole canopy level, we found that solar UV-B exclusion resulted in a two-foldincrease in the number of leaf lesions inflicted by various species of chewinginsects that naturally invaded the field plots. Leaves from canopies exposed tosolar UV-B showed significantly higher levels of soluble phenolics and lowerlevels of lignin than leaves that developed in canopies covered by polyesterfilms. No differences in specific leaf mass, leaf nitrogen or hemicellulosecontent were detected between the control and the solar-UV-B exclusiontreatments. Our results are consistent with the idea that present-day solar UV-B has an important regulatory influence on the interactions between plants and phytophagous insects.     

Zinc mediated effects on leaf CO2 diffusion conductances and net photosynthesis in Phaseolus vulgaris L.

Supra-optimal levels of zinc in primary leaves of Phaseolus vulgaris increased the CO₂ compensation point and inhibited net photosynthesis. Leaf morphology was modified: mesophyll intercellular area, stomatal slit length and interstomatal distance were reduced, but stomatal density increased. Internal and stomatal conductances to CO₂ diffusion decreased. These changes are discussed in relation to the observed effects on leaf gas exchange and to the previously reported inhibition of different photosynthetic and photorespiratory enzymes.     

Restriction fragment length polymorphism diversity in soybean

Summary Fifty-eight soybean accessions from the genus Glycine, subgenus Soja, were surveyed with 17 restriction fragment length polymorphism (RFLP) genetic markers to assess the level of molecular diversity and to evaluate the usefulness of previously identified RFLP markers. In general, only low levels of molecular diversity were observed: 2 of the 17 markers exhibited three alleles per locus, whereas all others had only two alleles. Thirty-five percent of the markers had rare alleles present in only 1 or 2 of the 58 accessions. Molecular diversity was least among cultivated soybeans and greatest between accessions of different soybean species such as Glycine max (L.) Merr. and G. soja Sieb. and Zucc. Principal component analysis was useful in reducing the multidimensional genotype data set and identifying genetic relationships.     

Photosynthetic acclimation and photosynthate partitioning in soybean leaves in response to carbon dioxide enrichment

Photosynthetic rates and photosynthate partitioning were studied in three-week-old soybean [Glycine max (L.) Merr. cv. Williams] plants exposed to either ambient (35 Pa) or elevated (70 Pa) CO₂ in controlled environment chambers. Ambient CO₂-grown plants also were given a single 24 h treatment with 70 Pa CO₂ 1 d prior to sampling. Photosynthetic rates of ambient CO₂-grown plants initially increased 36% when the measurement CO₂ was doubled from 35 to 70 Pa. Photosynthetic rates of the third trifoliolate leaf, both after 1 and 21 d of elevated CO₂ treatment, were 30 to 45% below those of ambient CO₂-grown plants when measured at 35 Pa CO₂. These reduced photosynthetic rates were not due to increased stomatal resistance and were observed for 2 to 8 h after plants given 1 d of CO₂ enrichment were returned to ambient CO₂. Initial and total ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities, percent activation, Rubisco protein, soluble protein and leaf chlorophyll content were similar in all CO₂ treatments. Quantum yields of photosynthesis, determined at limiting irradiances and at 35 Pa CO₂, were 0.049±0.003 and 0.038±0.005 mol CO₂ fixed per mol quanta for ambient and elevated CO₂-grown plants, respectively (p<0.05). Leaf starch and sucrose levels were greater in plants grown at 70 than at 35 Pa CO₂. Starch accumulation rates during the day were greater in ambient CO₂-grown plants than in plants exposed to elevated CO₂ for either 1 or 21 d. However, the percentage of C partitioned to starch relative to total C fixed was unaffected by 1 d of CO₂ enrichment. The above results showed that both photosynthetic and starch accumulation rates of soybean leaflets measured at 35 Pa CO₂ were temporarily reduced after 1 and 21 d of CO₂ enrichment. The biochemical mechanism affecting these responses was not identified.Abbreviations SLW- specific leaf weight (g m^–2) - Rubisco- ribulose 1,5-bisphosphate carboxylase/oxygenase - Rul- 5bisP, ribulose 1,5 bisphosphate - DAP- days after planting - SAR- starch accumulation rate - C_i- intercellular CO₂ concentration     

Interactive effects of cadmium and aluminum on growth and antioxidative enzymes in soybean

The effects of Al, Cd and pH on growth, photosynthesis, malondialdehyde (MDA) content, and some antioxidant enzyme activities of the two soybean cultivars with different Al tolerance were determined using a hydroponic culture. There were six treatments as follows: pH 6.5; pH 4.0; pH 6.5 + 1.0 μM Cd; pH 4.0 + 1.0 μM Cd; pH 4.0 + 150 μM Al; pH 4.0 + 1.0 μM Cd + 150 μM Al. The results showed that the low pH (4.0) and Al treatments caused marked reduction in the growth (root and shoot length and dry mass), chlorophyll content (SPAD value) and net photosynthetic rate. Higher malondialdehyde content, superoxide dismutase (SOD) and peroxidase (POD) activities were detected in the plants exposed to both Al and Cd than in those exposed to Al treatment alone. An expressive enhancement of SOD and POD was observed in the plants exposed to 150 μM Al in the comparison with the control plants, especially in Al-sensitive cv. Zhechun 2 which had also significantly higher Al and Cd content than Al tolerant cv. Liao-1. Cd addition increased Al content in the plants exposed to Al + Cd stress, and cv. Zhechun 2 had relatively lower Al content. The present research indicated that Al and Cd are synergistic in their effects on plant growth and some physiological traits.     

Very high CO2 partially restores photosynthesis in sunflower at low water potentials

We re-examined the question of whether the stomata limit photosynthesis in dehydrated sunflower (Helianthus annuus L.) plants having low leaf water potentials. A gas-exchange apparatus was modified to operate at external CO₂ partial pressures as high as 3000 Pa (3%), which were much higher than previously achieved. This allowed photosynthesis and stomatal behavior to be monitored simultaneously at very high CO₂ in the same leaf. The data were compared with those from leaves treated with abscisic acid (ABA) where effects on photosynthesis are entirely stomatal. Photosynthesis was inhibited at low water potential and was only slightly enhanced by increasing the external CO₂ partial pressure from 34 Pa (normal air) to 300 Pa. Photosynthesis in ABA-treated leaves was similarly inhibited but recovered fully at 300 Pa. In both cases, the stomata closed to the same extent as judged from the average conductance of the leaves. Because the ABA effect resulted from diffusion limitation for CO₂ caused by stomatal closure, the contrasting data show that most of the dehydration effect was nonstomatal at low water potentials. When CO₂ partial pressures were raised further to 3000 Pa, photosynthesis increased somewhat at low water potentials but not in ABA-treated leaves. This indicates that some nonstomatal component of photosynthesis responded differently in leaves at low water potential and leaves treated with ABA. Because this component was only partially restored by very high CO₂, it was likely to be metabolic and was an important source of photosynthetic inhibition.Abbreviations and Symbol ABA abscisic acid - Chl chlorophyll - p_a external partial pressure of CO₂ - P_i intercellular partial pressure of CO₂ - _w water potential This work was supported by grant DE-FG02-87ER13776 from the Department of Energy and a grant from E.I. DuPont de Nemours and Company.     

Macronutrient concentrations of soybean infected with soybean cyst nematode

Soybean cultivars (Glycine max(L.) Merr.) infected with soybean cyst nematode (SCN; Heterodera glycinesIchinohe) often show symptoms similar to K deficiency. The objectives of this experiment were to determine if SCN infection affected macronutrient concentrations in soybean seedling vegetative tissues, determine whether increased K fertility can overcome these possible effects, and to determine if these possible effects are localized at the site of infection or expressed systemically throughout the root system. Soybean plants were grown with root systems split into two halves. This allowed differential K (0.2, 2.4 and 6.0 mM K nutrient solutions) and SCN (0 and 15 000 eggs/plant) treatments to be applied to opposite root-halves of the same plant. Thirty days after plants were inoculated with SCN, macronutrient concentrations of shoot and root tissues were determined. Potassium concentration in leaf blades was not affected; but K concentrations in leaf-petiole and stem tissues were increased with SCN infection. Roots infected with SCN contained lower K concentrations than uninfected roots, but only for the 2.4 mM K treatment. Thus, at the medium level of K fertility, SCN reduced K concentration in soybean roots, and increasing K fertility to the high level overcame the effect. Because K concentrations in the shoot tissues were not reduced by SCN infection, above ground portions of the plant may be able to overcome limitations that occur in roots during the first 30 days of infection. Increasing K fertility level in soybean fields may not benefit vegetative growth of soybean infected with SCN.