Photosynthesis In Soybean Research Articles

Carbon dots promoted soybean photosynthesis and amino acid biosynthesis under drought stress: Reactive oxygen species scavenging and nitrogen metabolism

With global warming and water scarcity, improving the drought tolerance and quality of crops is critical for food security and human health. Here, foliar application of carbon dots (CDs, 5 mg·L−1) could scavenge reactive oxygen species accumulation in soybean leaves under drought stress, thereby enhancing photosynthesis and carbohydrate transport. Moreover, CDs stimulated root secretion (e.g., amino acids, organic acids, and auxins) and recruited beneficial microorganisms (e.g., Actinobacteria, Ascomycota, Acidobacteria and Glomeromycota), which facilitate nitrogen (N) activation in the soil. Meanwhile, the expression of GmNRT, GmAMT, and GmAQP genes were up-regulated, indicating enhanced N and water uptake. The results demonstrated that CDs could promote nitrogen metabolism and enhance amino acid biosynthesis. Particularly, the N content in soybean shoots and roots increased significantly by 13.2 % and 30.5 %, respectively. The amino acids content in soybean shoots and roots increased by 257.5 % and 57.5 %, respectively. Consequently, soybean yields increased significantly by 21.5 %, and the protein content in soybean kernels improved by 3.7 %. Therefore, foliar application of CDs can support sustainable nano-enabled agriculture to combat climate change.

Soybean photosynthesis and crop yield are improved by accelerating recovery from photoprotection.

Crop leaves in full sunlight dissipate damaging excess absorbed light energy as heat. This protective dissipation continues after the leaf transitions to shade, reducing crop photosynthesis. A bioengineered acceleration of this adjustment increased photosynthetic efficiency and biomass in tobacco in the field. But could that also translate to increased yield in a food crop? Here we bioengineered the same change into soybean. In replicated field trials, photosynthetic efficiency in fluctuating light was higher and seed yield in five independent transformation events increased by up to 33%. Despite increased seed quantity, seed protein and oil content were unaltered. This validates increasing photosynthetic efficiency as a much needed strategy toward sustainably increasing crop yield in support of future global food security.

Effects of plant density, nitrogen rate and supplemental irrigation on photosynthesis, root growth, seed yield and water-nitrogen use efficiency of soybean under ridge-furrow plastic mulching

The ridge-furrow plastic mulching system has been reported to increase crop yield and water-nitrogen use efficiency in semi-arid and semi-humid regions, but the effects of plant density, nitrogen (N) rate and supplemental irrigation on chlorophyll, photosynthesis, root growth and seed yield of soybean under ridge-furrow plastic mulching are poorly understood. A two-year field experiment (2019 and 2020) was conducted on soybean in a split-split plot design, with two plant densities (D16: 160,000 plants ha−1; D32: 320,000 plants ha−1) as main plots, two N rates (N30: 30 kg N ha−1; N60: 60 kg N ha−1) as sub plots, and two irrigation levels (W0: rainfed; W30: supplemental irrigation of 30 mm at the flowering-podding stage) as sub-sub plots. The results showed that plant density, N rate and supplemental irrigation had significant effects on leaf chlorophyll content, chlorophyll fluorescence parameters, photosynthesis, aboveground/root growth and seed yield. Increasing plant density enhanced leaf area index (LAI) by 31.9% and aboveground biomass (AGB) by 59.4%, seed yield by 27.4%, water use efficiency of seed yield (WUEs) by 27.9% and nitrogen partial factor productivity (NPFP) by 26.6%. Increasing N rate increased leaf chlorophyll content by 11.9% and photosynthetic rate by 5.5%, thereby increasing LAI by 11.5%, AGB by 10.3%, seed yield by 8.9% and WUEs by 8.2%. Supplemental irrigation increased chlorophyll content by 7.6% and photosynthetic rate by 3.7%, thereby increasing LAI by 4.7%, AGB by 11.0%, seed yield by 4.7% and NPFP by 4.0%, while supplemental irrigation only increased WUEs under D32. Compared with D16N30W0, D32N60W30 enhanced seed yield by 44.0% and WUEs by 37.0%, but reduced NPFP by 28.8%. Compared with D32N30W30, D32N60W30 increased both seed yield and WUEs by 8.5%, but it reduced NPFP by 45.5% with 100% higher N input. LAI, AGB, WUEs, NPFP and some leaf physiological (EXC, Chla/Chlb, EWTleaf and Ls) and root (TRLD, TRVD and TRSD) indexes were closely related to soybean yield. This study provides a better understanding how plant density, N rate and supplemental irrigation improved soybean productivity and water-nitrogen use efficiency by regulating chlorophyll, photosynthesis and aboveground/root growth.

Photosynthesis, Yield and Quality of Soybean (Glycine max (L.) Merr.) under Different Soil-Tillage Systems

Due to current climate changes and drought periods, it is recommended to cultivate soybean in no-plowing tillage systems. The conducted research is to contribute to a partial explanation of the course of photosynthesis processes in soybean plants, which may facilitate the decision making before sowing this species in a given tillage system. The aim of the study was to assess the dependence of photosynthesis on the yield and variable hydrothermal conditions of tillage systems, as well as their impact on the productivity and quality of soybean. A field experiment was carried out using soybean cv. Merlin, between 2017 and 2019 in Boguchwała, Poland. The plant tested was soybean cv. Merlin. The tillage systems—conventional (CT), reduced (RT) and no-tillage (NT)—were the experimental factors. The use of CT and RT influenced growth in leaf area index (LAI) and soil plant analysis development (SPAD) and improved the photosynthesis process, which increased the values of the maximal quantum yield of the photolysis system of the donor side of PSII (Fv/F0), and performance index of PS II (PI) and net photosynthetic rate (PN), stomatal conductance (gs) parameters, compared to NT. CT treatment increased the yield of soybean plants to significantly higher compared with NT treatment, and seeds treated with the CT treatment contained more protein. The content of fat and phosphorus (P) were significantly higher in the NT system and the content of potassium (K) from RT. In 2017, under drought conditions (the June–September period), the seed yield of NT was similar to the yield of CT and significantly higher than the yield of RT. The higher value of hydrothermal coefficients in 2019 resulted in an increase in photosynthesis parameters, seed yield as well as the content of fat and elements P and K.

Photosynthesis and Fine Root Growth Dynamics of Soybean in Walnut-Soybean Agroforestry System.

Agroforestry system is regarded as a promising practice in sustainable agricultural management. However, the effects of long-term tree-based intercropping on crop remain poorly understood, especially in the Loess Plateau (China). In this study, the impacts of photosynthetic and respiration rate were determined by the portable photosynthesis system (Li-6400), and the effects of the root growth dynamics of soybean in the walnut-soybean intercropping system were measured by soil auger and WinRHIZO root analysis system, in the Loess Plateau. The results showed that soybean reached the highest net photosynthetic rate during flowering period, with the net photosynthetic rate of intercropped soybean, which was 20.40 μmol·m−2·s−1, significantly higher than that of its monocropped counterpart. Soybean biomass reached the maximum during the pod-bearing period, with intercropped soybean biomass being 25.49 g, significantly higher than that of its monocropped counterpart. The mean diameter and increased density of soybean fine roots reduced along with increased soil depth. Both the diameter (0.43 mm) and increased density (930 cm/dm3) of intercropped soybean fine roots were evidently higher than those of monocropped soybean (0.35 mm, 780 cm/dm3). With increasing cropping years, fine roots of intercropped soybean tended to be mainly distributed in soil at a depth between 0 and 20 cm from the fifth year. Collectively, compared with soybean monoculture, walnut-soybean agroforestry system is more conducive to soybean growth in the Loess Plateau.

Growth, photosynthesis and yield of soybean in ridge-furrow intercropping system of soybean and flax

It is of practical significance to control the excessive vegetative growth of soybean during the rainy season, which causes a reduction in yield. In this study, we adopted soybean flax ridge-furrow intercropping system in order to constrain soybean’s excessive vegetative growth by interspecific competition between intercrops and estimated the growth, photosynthesis and yield of soybean. Two-year-experiment was conducted in 2018 and 2019 in the experimental farm of KIM IL SUNG University. Soybean seeds were grown in ridges and flax seeds were in furrows between ridges. During the co-growth stage, the early growth of soybean intercropped with flax was depressed by interspecific competition. At 45 days after soybean sowing, just before flax harvest, the average height and stem diameter of intercropped soybean plant were 22.5 cm and 0.7 mm shorter than those of sole cropped soybean plant, respectively. At the reproductive growth stage, the height of intercropped soybean plant was still 18.5 cm shorter than sole cropped soybean, while other agronomic parameters, including leaf area index (LAI), dry matter per plant, photosynthetic rate and chlorophyll contents, were greater for intercropped soybean. This led to higher yield of soybean (118.5%) and land equivalent ratio (LER) (203.5%) in ridge-furrow intercropping, as compared to sole cropping. Our results suggest that ridge-furrow intercropping system can be an effective way to constrain soybean’s excessive vegetative growth during the rainy season and improve soybean seed yield and LER.

Diminishing toxicity of pyrene on photosynthetic performance of soybean using Bacillus subtilis (NCIM 5594).

Polycyclic aromatic hydrocarbons are persistent organic pollutants causing serious environmental problems, being toxic to plants and difficult to remediate. Pyrene is one such extremely dangerous compound that is toxic for the environment. This study suggests the use of Bacillus subtilis (National Collection of Industrial Microorganisms [NCIM] 5594) to overcome inhibitory effects of pyrene on soybean photosynthesis. The toxicity of pyrene to soybean was evident from a significant decrease in seed germination parameters, photosynthetic performance and biomass during growth of soybean in pyrene contaminated soil. Efficiency of performance index, light absorption, trapping and electron transport were reduced in plants grown in pyrene contaminated soil while significant recovery in these parameters was observed in plants grown in pyrene+B. subtilis treated soil. Activity levels of dehydrogenase and lipase enzymes significantly recovered in pyrene+B. subtilis treated soil. After extraction of pyrene from soil and soybean plant, concentration of pyrene was lowered in pyrene+B. subtilis treated soil and plants. These findings suggest efficient degradation of pyrene by B. subtilis . About 70% degradation of pyrene was achieved in soil using B. subtilis ; thus it is a useful strain for crop improvement in pyrene polluted soil.

Efficiency of soybean photosynthesis as affected by the components of cultivation technology

Purpose. Determine the efficiency of photosynthesis of soybean varieties ‘Ustia’, ‘Kordoba’, ‘Estafeta’ as affected by the use of microfertilizers and growth regulators.
 Methods. Field, laboratory.
 Results. The article presents the results of research to study the effectiveness of photosynthesis in the cultivation of different varieties of soybean. It was found that the treatment of plants with microfertilizer Yara Vita Mono Molitrak in the budding phase (0.25 l/ha) + in the flowering phase (0.25 l/ha) in combination with the growth regulator Radostym ensured a leaf area (1000 m2/ha) increase of 7.2 m2/ha in variety ‘Ustia’, 7.6 in ‘Kordoba’ and 5.2 in ‘Estafeta’, compared to control. At the same time, the efficiency of using the growth regulator Biosil against the background of double treatment with the microfertilizer was at the level of the treatments with single treatments with Yara Vita Mono Molitrak in the budding phase (0.25 l/ha) in combination with appropriate growth regulators.
 Conclusions. It was investigated that the leaf surface area of ‘Ustia’ variety with foliar fertilization using Yara Vita Mono Molitrak microfertilizer in the budding phase (0.25 l/ha) in combination with growth regulators Biosil and Radostym was 38.8 and 39.2 thousand m2/ha. The use of microfertilizers twice in combination with the above-mentioned growth regulators contributed to the increase of leaf area to the level of 38.9 and 39.5 thousand m2/ha, respectively. Similarly, in ‘Kordoba’ soybean variety, the best option was the use of Yara Vita Mono Molitrak in the budding phase (0.25 l/ha) + in the flowering phase (0.25 l/ha) in combination with the growth regulator Radostym, which helped to increase the leaf area to 39.5 thousand m2/ha. Foliar fertilization with microfertilizers combined with the use of growth regulators provides the formation of maximum NPP. Thus, in ‘Ustia’ variety, it was 1.47 and 1.45 g/m2, in ‘Estafeta’ 1.82 and 1.82 g/m2 of dry matter per day.

Вплив мінеральних добрив та біопрепарату на ріст та розвиток рослин сої

The soybean (Glycine max) is one of the most important food plants of the world, and seems to be growing in importance. It is an annual crop, fairly easy to grow, that produces more protein and oil per unit of land than almost any other crop. It is a versatile food plant that, used in its various forms, is capable of supplying most nutrients. It can substitute for meat and to some extent for milk. It is a crop capable of reducing protein malnutrition. In addition, soybeans are a source of high value animal feed. Nevertheless, the soybean is adapted primarily to the Temperate Zone. Each improved variety has an adaptation determined in large part by latitude. Soybean requires careful home processing to bring out its best qualities, and if not well prepared, it has an off-flavor that is seldom appreciated Soybeans need to be inoculated with a particular strain of Rhizobium fungus before planting. This fungus fixes nitrogen (i. e. takes elemental nitrogen from the air and adds it to the soil in a form that the soybean plant can use). However, if soybeans are planted in a field that contained soybeans as a previous crop, they may not require inoculation because the Rhizobium will still be in the soil. If soybeans are not grown in association with Rhizobium, they will grow more slowly, require nitrogen fertilizer, and yield less. Rhizobium inoculum must be fresh (viable) and is usually purchased with the seed. If Rhizobium inoculum is not available in a particular area, and soybeans are not now being grown, it may be difficult to produce this crop. Soybeans need fertilizer, including both the macronutrients phosphorous and potassium (P and K) and sometimes micronutrients. Nitrogen is not required if soybeans are properly inoculated. Soybeans need rather large amounts of phosphorous, calcium, magnesium, and sulfur. Minor elements are sometimes required. Soybeans cannot be recommended for unfertilized soils. For optimum soybean yield, it is necessary to use both biological N2-fixation and nitrogen uptake by soybean roots. Nitrogen fertilizer applied to soybean is based on the plant nitrogen needs during seedling development prior to nodule formation that is crucial to the growth and development of soybean As with all crops, soybean yield is the result of the net accumulation of organic compounds assimilated through photosynthesis. Research on soybean photosynthesis conducted during the 1950’s and 1960’s found that several cultivars grown at that time became light saturated. However, much of those data were collected from plants grown in a greenhouse or other artificial environment. Much of the information on the response of soybean photosynthesis to changing light levels however is dated, having been published prior to 1985, with cultivars that are no longer in production, using less portable and sophisticated instrumentation than is now available. In the article are presented results of researching peculiarities of growth development and formation of soybean photosynthetic productivity depending on weather conditions, level of mineral fertilization and different application methods of biological product on the chelate form under conditions of the Right-bank Forest-Steppe. It is established that a systematic approach to soybean nutrition, namely its cultivation on the background of optimal doses of mineral fertilizers N30P45K45 and the use of biological product Organic-Balance for seed treatment in combination with foliar feeding creates the best conditions for growth, development and preservation of maximum plants full ripeness, which is the basis for obtaining high grain yields.

Photosynthesis, yield, energy balance, and water-use of intercropped maize and soybean.

By 2050, the U.S. Corn Belt will likely face a 23% increase in leaf‐to‐air vapor pressure deficit (VPDL), the driving force of evapotranspiration (ET), which may restrict maize yield improvements for rainfed agroecosystems. Alternative cropping systems, such as maize and legume intercrops, have previously demonstrated yield and resource‐use advantages over monocultures. In this study, the residual energy balance approach was used to gain insights into how an additive simultaneous maize and soybean intercrop system regulates ET and water‐use efficiency (WUE) compared to standard maize and soybean monoculture systems of the U.S. Corn Belt. Experimental field plots were rain‐fed and arranged in a randomized complete block design in three blocks. Photosynthetic capacity and grain yield of maize were conserved in the intercrop. However, its competitive dominance shaded 80%–90% of incident light for intercropped soybean at canopy closure, leading to a 94% decrease in grain yield compared to soybean monoculture. The total grain yield per unit area of the additive intercrop (land‐use efficiency) increased by 11% ± 6% (1 SE). Compared to maize monoculture, the intercrop had higher latent heat fluxes (λET) at night but lower daytime λET as the intercrop canopy surface temperature was approximately .25°C warmer, partitioning more energy to sensible heat flux. However, the diel differences in λET fluxes were not sufficient to establish a statistically significant or biologically relevant decrease in seasonal water‐use (ΣET). Likewise, the increase in land‐use efficiency by the intercrop was not sufficient to establish an increase in seasonal water‐use efficiency. Intercropping high‐performing maize and soybean cultivars in a dense configuration without negative impact suggests that efforts to increase yield and WUE may lead to improved benefits.

Short Term Elevated CO2 Interacts with Iron Deficiency, Further Repressing Growth, Photosynthesis and Mineral Accumulation in Soybean (Glycine max L.) and Common Bean (Phaseolus vulgaris L.)

Elevated CO2 (eCO2) has been reported to cause mineral losses in several important food crops such as soybean (Glycine max L.) and common bean (Phaseolus vulgaris L.). In addition, more than 30% of the world’s arable land is calcareous, leading to iron (Fe) deficiency chlorosis and lower Fe levels in plant tissues. We hypothesize that there will be combinatorial effects of eCO2 and Fe deficiency on the mineral dynamics of these crops at a morphological, biochemical and physiological level. To test this hypothesis, plants were grown hydroponically under Fe sufficiency (20 μM Fe-EDDHA) or deficiency (0 μM Fe-EDDHA) at ambient CO2 (aCO2, 400 ppm) or eCO2 (800 ppm). Plants of both species exposed to eCO2 and Fe deficiency showed the lowest biomass accumulation and the lowest root: shoot ratio. Soybean at eCO2 had significantly higher chlorophyll levels (81%, p < 0.0001) and common bean had significantly higher photosynthetic rates (60%, p < 0.05) but only under Fe sufficiency. In addition, eCO2 increased ferric chelate reductase acivity (FCR) in Fe-sufficient soybean by 4-fold (p < 0.1) and in Fe-deficient common bean plants by 10-fold (p < 0.0001). In common bean, an interactive effect of both environmental factors was observed, resulting in the lowest root Fe levels. The lowering of Fe accumulation in both crops under eCO2 may be linked to the low root citrate accumulation in these plants when grown with unrestricted Fe supply. No changes were observed for malate in soybean, but in common bean, shoot levels were significantly lower under Fe deficiency (77%, p < 0.05) and Fe sufficiency (98%, p < 0.001). These results suggest that the mechanisms involved in reduced Fe accumulation caused by eCO2 and Fe deficiency may not be independent, and an interaction of these factors may lead to further reduced Fe levels.

Predicting biochemical acclimation of leaf photosynthesis in soybean under in-field canopy warming using hyperspectral reflectance.

Traditional gas exchange measurements are cumbersome, which makes it difficult to capture variation in biochemical parameters, namely the maximum rate of carboxylation measured at a reference temperature (Vcmax25 ) and the maximum electron transport at a reference temperature (Jmax25 ), in response to growth temperature over time from days to weeks. Hyperspectral reflectance provides reliable measures of Vcmax25 and Jmax25 ; however, the capability of this method to capture biochemical acclimations of the two parameters to high growth temperature over time has not been demonstrated. In this study, Vcmax25 and Jmax25 were measured over multiple growth stages during two growing seasons for field-grown soybeans using both gas exchange techniques and leaf spectral reflectance under ambient and four elevated canopy temperature treatments (ambient+1.5, +3, +4.5, and +6°C). Spectral vegetation indices and machine learning methods were used to build predictive models for Vcmax25 and Jmax25 , based on the leaf reflectance. Results showed that these models yielded an R2 of 0.57-0.65 and 0.48-0.58 for Vcmax25 and Jmax25 , respectively. Hyperspectral reflectance captured biochemical acclimation of leaf photosynthesis to high temperature in the field, improving spatial and temporal resolution in the ability to assess the impact of future warming on crop productivity.

Root K Affinity Drivers and Photosynthetic Characteristics in Response to Low Potassium Stress in K High-Efficiency Vegetable Soybean.

Significant variations of potassium absorption and utilization exist in vegetable soybean. Pot and hydroponic experiments were carried out to examine the characteristics of root potassium (K) affinity-associated drivers and photosynthesis in vegetable soybean (edamame) [Glycine max (L.) Merr.] with different K efficiency. Two K high-efficiency vegetable soybean genotypes (Line 19 and Line 20) and two K low-efficiency genotypes (Line 7 and Line 36) were investigated in low K and normal K conditions. The root of K high-efficiency genotypes had a higher K+ affinity associated with a higher maximum K+ uptake rate (Imax), but lower Michaelis constant for K+ absorption (Km) and lower compensation concentration for K+ uptake (Cmin). Seedlings of K high-efficiency genotypes also had higher root vigor [triphenyl tetrazolium chloride (TTC) reduction method] and greater absorbing activity (methylene blue method), especially in the low K condition. Furthermore, the root bleeding-sap rate of K high-efficiency genotypes in low K stress was 9.9–24.3% greater than that of normal K conditions, which was accompanied by a relatively higher K concentration of root bleeding-sap in contributing to K+ upward flux. The root of K high-efficiency vegetable soybean genotypes exhibited K+ high-affinity and driving advantages. Photosynthetic parameters of K high-efficiency vegetable soybean genotypes were less affected by low K stress. Low K stress decreased the net photosynthetic rate of K high-efficiency genotypes by 6.1–6.9%, while that of K low-efficiency genotypes decreased by 10.9–15.7%. The higher chlorophyll (Chl) a/b ratio with enhanced relative content of Chl a in response to low K stress might be an adapted mechanism for K high-efficiency genotypes to maintain photosynthetic capacity. Stronger root K affinity drivers associated with photosynthetic adaptability to low K stress are the key factors in determining the K high-efficiency of vegetable soybeans.

Distribution characteristics of climate potential productivity of soybean in frigid region and its response to climate change.

The scope of this study is to analyze the climatic potential productivity of soybean [Glycine max (L.) Merr.] and explore the impact of climate change on soybean in the frigid region in China by using daily climatic variables from 144 meteorological stations for the period 1971‒2019. The gradually descending model is used to estimate photosynthesis, light-temperature, and climatic potential productivity of soybean. The results show thatclimate potential productivity of soybean in the frigid region ranges from large to small: Liaoning > Jilin > Heilongjiang > East Four Leagues (four cities in eastern Inner Mongolia), with Heilongjiang and East Four Leagues showing a significant upward trend. Spatially, the climate potential productivity is larger on plains than that on mountains. The Northeast Plain and Sanjiang Plain are areas with high climate potential productivity. Changes in climatic factors have different impacts on the climate potential productivity of soybean. The influence of temperature changes on the climate potential productivity shows a positive effect, and climate warming compensates for the lack of heat in the frigid region. Furthermore, radiation and precipitation are the main climatic factors leading to spatial differences in the climate potential productivity of soybean in the frigid region. Radiation changes have a positive effect on soybean climate potential productivity in plain areas and a negative effect on the mountains. However, precipitation reduction negatively affects most of the frigid region, while it has a positive effect on the two plains of Heilongjiang. Precipitation responses the needs of soybean growth. Our findings recommend that a transition of soybean planting from the mountainous region to plain, that is, from low potential productivity areas to high potential productivity areas, could be an effective strategy for regional optimization for planting structure and rational utilization of irrigation technology.

Effects of exposure of the leaf abaxial surface to direct solar radiation on the leaf anatomical traits and photosynthesis of soybean (Glycine max L.) in dryland farming systems

The frequent occurrence of monsoon winds usually leads to the formation of inverted soybean leaves. However, the effect of leaf inversion on photosynthetic capacity remains unclear. The responses of leaf anatomical traits, chlorophyll fluorescence induction kinetics parameters, photosynthetic capacity, and nonstructural carbohydrates of fully expanded leaves to inversion of leaves in two soybean cultivars were studied. Leaf inversion decreased the stomatal size and thickness of developed leaves. The net photosynthetic rate was significantly reduced under leaf inversion, which resulted from reduced excitation energy trapping and electron transport of PSII reaction center. Leaf inversion increased leaf temperature 10 d after leaf inversion but reduced the instantaneous water-use efficiency compared to normally oriented leaves. Due to the decreased light-saturated net photosynthetic rate, the soluble sugars of light-sensitive cultivar decreased significantly. In summary, leaf inversion deactivated the PSⅡ reaction centers, reduced photosynthesis and nonstructural carbohydrates in upper canopy soybean leaves.

Effects of Planting Density of Spring Soybean on Canopy Photosynthetically Active Radiation and Yield in Northeast China

Soybean is an important legume crop. Planting density of soybean directly affects the distribution of photosynthetically active radiation (PAR) in the canopy, which affects the physiological changes, such as photosynthesis of soybean, and leads to the change of yield. In this experiment, soybean variety Heinong 84 was adopted, and five planting densities were set as 200,000 plants/ha (D20), 250,000 plants/ha (D25), 300,000 plants/ha (D30), 400,000 plants/ha (D40) and 500,000 plants/ha (D50). The canopy PAR intensity was measured based on photosynthetically active radiation recorder, and the effects of different densities on soybean canopy PAR and yield were studied systematically. According to the results, with the extension of growth period, the PAR above and within the canopy of soybean decreased first and then increased, and the rules were consistent under different densities. During each growth period, PAR was above that of canopy > growth point > middle stem > cotyledon scar and decreased with the increase of density. The growth point changed significantly, followed by middle stem, but no significant change happened in cotyledon scar. The absorption photosynthetically active radiation (FPAR) showed a unimodal trend with the increase of density at V4 and R2 and had an upward trend at R4 and R6. The number of effective pods per plant and 100 seed weight of D20 are the highest, and the yield of D25 is the highest.

Prohexadione-calcium alleviates saline-alkali stress in soybean seedlings by improving the photosynthesis and up-regulating antioxidant defense

Soil salinization seriously restricts the growth and yield of soybeans. However, little information is available on the early growth stages of soybeans which are subjected to the gibberellin biosynthesis inhibitor, prohexadione-calcium (Pro-Ca). This study aimed to investigate the effects of exogenous Pro-Ca on saline-alkali stress-induced damages to photosynthesis and antioxidant defenses in soybean (Glycine max L.) seedlings. At the V3 growth stage, salt-tolerant genotype Hefeng 50 (HF50) and salt-sensitive genotype Kenfeng 16 (KF16) were subjected to 110 mmol L−1 mixed saline-alkali stress respectively, and then 100 mg L−1 Pro-Ca was sprayed on the leaves. Our results showed that saline-alkali stress accelerated the degradation of thylakoids, inhibited chlorophyll synthesis, reduced shoot dry weight, electron transfer rate (ETR), and peroxidase (POD) activity, the concentration of ascorbic acid (AsA) and soluble sugar, but enhanced the concentration of proline, hydrogen peroxide (H2O2) and the rate of superoxide radical (O2∙−) generation. Additionally, saline-alkali stress induced a lower decrease of the net photosynthetic rate (Pn), potential activity of PSII (Fv/F0), and maximum quantum yield of PSII (Fv/Fm) in salt-tolerant HF50 than in salt-sensitive KF16. Nevertheless, foliar spraying of exogenous Pro-Ca increased the chlorophyll content, Pn, Fv/F0, and Fv/Fm. These results were more prominent when Pro-Ca was applied to KF16 under saline-alkali conditions. Furthermore, exogenous application of Pro-Ca retarded the degradation of thylakoids, increased the ETR and the accumulation of AsA, soluble sugar, and proline, activated the activities of superoxide dismutase (SOD), catalase (CAT), and POD, and decreased the concentration of malondialdehyde (MDA), electrolyte leakage (EL), O2∙−, and H2O2. These results indicated that Pro-Ca could effectively protect soybean seedlings against damage from saline-alkali stress by regulating seedling phenotype, photosynthetic apparatus, antioxidant defense, and osmoregulation.

Effect of Ti treatments on growth, photosynthesis, phosphorus uptake and yield of soybean (Glycine max L.) in maize-soybean relay strip intercropping

Shade is the main growth and yield limiting factor for soybean seedlings in maize-soybean relay strip intercropping. Therefore, a field experiment was conducted to investigate the effect of titanium (Ti) foliar application on soybean under a maize-soybean relay strip intercropping system. In this study, the soybean plants were sprayed with Ti treatments (T0S = 0, T1S = 125, T2S = 250, T3S = 500 and T4S = 1000 mg L−1) under maize-soybean relay strip intercropping. The results have indicated that under intercropping environment, Ti application significantly affected the growth of the plants. The soybean plants supplied with Ti treatment (T1S) significantly improved soybean diameter and stem strength at both V5 and R5 stages. Ti application resulted in a significant increase in SPAD values in T1S (i.e. 31.69 % and 21.21 %) and T2S (i.e. 21.55 % and 22.19 %) in comparison to control at both V5 and R5 stage, respectively. Furthermore, foliar application of Ti (T1S) significantly increased photosynthetic rate by 33.15 % and 22.80 % at both V5 and R5 stages. The stomatal conductance (Gs) increased significantly in T1S (44.39 %) and T2S (31.30 %) at the V5 stage and in T1S (29.85 %) at the R5 stage, respectively in comparison to control leading to increase root and shoot biomass in both V5 and R5 stages except for treatment T4S. Analysis of stem anatomical structure, stem strength (lodging resistance), and phosphorus content revealed that foliar application of Ti not only improved the shade tolerance but also increased yield (16–17 %) of soybean under maize-soybean relay strip intercropping. Conclusively, foliar application of Ti could be helpful in mitigating the shade stress and increasing soybean yield under the strip intercropping system.

Na+ and/or Cl- Toxicities Determine Salt Sensitivity in Soybean (Glycine max (L.) Merr.), Mungbean (Vigna radiata (L.) R. Wilczek), Cowpea (Vigna unguiculata (L.) Walp.), and Common Bean (Phaseolus vulgaris L.).

Grain legumes are important crops, but they are salt sensitive. This research dissected the responses of four (sub)tropical grain legumes to ionic components (Na+ and/or Cl−) of salt stress. Soybean, mungbean, cowpea, and common bean were subjected to NaCl, Na+ salts (without Cl−), Cl− salts (without Na+), and a “high cation” negative control for 57 days. Growth, leaf gas exchange, and tissue ion concentrations were assessed at different growing stages. For soybean, NaCl and Na+ salts impaired seed dry mass (30% of control), more so than Cl− salts (60% of control). All treatments impaired mungbean growth, with NaCl and Cl− salt treatments affecting seed dry mass the most (2% of control). For cowpea, NaCl had the greatest adverse impact on seed dry mass (20% of control), while Na+ salts and Cl− salts had similar intermediate effects (~45% of control). For common bean, NaCl had the greatest adverse effect on seed dry mass (4% of control), while Na+ salts and Cl− salts impaired seed dry mass to a lesser extent (~45% of control). NaCl and Na+ salts (without Cl−) affected the photosynthesis (Pn) of soybean more than Cl− salts (without Na+) (50% of control), while the reverse was true for mungbean. Na+ salts (without Cl−), Cl− salts (without Na+), and NaCl had similar adverse effects on Pn of cowpea and common bean (~70% of control). In conclusion, salt sensitivity is predominantly determined by Na+ toxicity in soybean, Cl− toxicity in mungbean, and both Na+ and Cl− toxicity in cowpea and common bean.

Effects of exogenous \u03b1-oxoglutarate on proline accumulation, ammonium assimilation and photosynthesis of soybean seedling (Glycine max(L.) Merr.) exposed to cold stress

The objective of this study was to examine the effects of exogenous α-oxoglutarate on leaf proline accumulation, ammonium assimilation and photosynthesis of soybean when exposed to cold stress. To achieve this objective, exogenous α-oxoglutarate was sprayed to potted seedlings of Henong60 and Heinong48 at 0, 2.5, 5.0 and 7.5 mmol/L, identified as A0, A2.5, A5.0, and A7.5, respectively. Leaf samples were collected after cold stress of 24 h (S1 stage) and 48 h (S2 stage). The results indicated that exogenous α-oxoglutarate significantly enhanced leaf GS activity, NADP-GDH activity, glutamate content, proline content and photosynthesis of soybean seedling exposed to cold stress at S1 and S2 stages. The ammonium content in leaf was significantly decreased by exogenous α-oxoglutarate at both stages. 5.0 mmol/L of exogenous α-oxoglutarate is the optimum concentration in this study. Leaf proline content for Henong60 and Heinong48 at A5.0 was 37.53% and 17.96% higher than that at A0 at S1 stage, respectively. Proline content for Henong60 and Heinong48 increased by 28.82% and 12.41% at A5.0 and A0, respectively, at S2 stage. Those results suggested that exogenous α-oxoglutarate could alleviate the adverse effects of cold stress.