The Ecophysiology Mechanism Of Soybean With Different Yield Performance Adapted To Water-Limited And Phosphorus-Deficit Environment

Soybean [Glycine max(L). Merrill.] had nitrogen-fixed ability and was the main protein source, soybean had important roles in agricultural ecosystem and sustainable development. Drought and low phosphorus(P) availability were the main factor limited the yield in soybean in Loess Plateau. Studying the eco-physiology mechanism evolved in yield performance under drought and low P availability was one way to breeding new cultivars with high yield. In this study, we used soybean cultivars with different breeding ear to investigate the eco-physiology mechanism of soybean adapted to drought and low P availability, and it can help us to breeding new cultivars with high yield under drought and low P availability.Experiment 1: Eight soybean genotypes(4 landrace genotypes: huangsedadou(HD),Longxixiaohuangpi(LX), Bailudou(BLD) and Xiaoheidou(XHD);4 modern cultivars:Jindou 21(J21),Jindou 19(J19),Jidou 12(J12) and Zhonghuang 30(ZH)) collected in Loess Plateau were grown in 1.33 m long PVC cyclinder(total weight for each cyclinder: 40.35 kg, total number: 128) used to evaluate the yield performance and water use pattern, root traits and water uptake under three soil moisture treatments imposed from 40 days after sowing: {well-watered [WW, maintained between 85-100% field capacity(FC)], drought-rewater cycle(RWS, water withheld until SWC decreased to 30% FC and then rewatered to 100% FC), and terminal water stress(TWS, water withheld until maturity)}.Root hydraulic conductance represent the water uptake rate. In order to investgate the ralationship between the root traits and root water uptake rate, the second experiment was conducted to determine the root hydraulic conductance at flowering and full seed stage under WW and RWS conditions.Experiment 2: We carried out a pot experiment to investigate the ecophysiology mechanism of soybean adapted to water and P deficits. Four soybean genotypes(2 landrace genotypes: Huangsedadou(HD), Bailudou(BLD); 2 recent genotypes: Jindou 21(J21) and Zhonghuang 30(ZH)) with different grain yields under drought in experiment 1 grown in 105 cm long PVC cyclinder(total weight for each cyclinder: 28.5 kg, total number: 144) were subjected to two water treatments(well-watered(WW, 85-100% FC), drought-rewater cycle(RWS, 30-100% FC)) and three P levels(applied 0(P0), 60(P60) and 120(P120) mg P kg–1 dry soil). The main results as followed:The main results as followed:Experiment 1:1, The recent genotypes had significantly higher grain yield and water use efficiency for grain yield than land-race genotypes under three water treatments. the water use was lower in the recent genotypes than the land-race genotypes under WW and RWS.2, Increased the water use after flowering significantly increased the flower and tagged pod number. Reducing the water use before flowering increased the after use after flowering under TWS. The recent genotypes with lower water use had significantly high grain yield under drought, thus reducing the water use improved the grain yield under drought.3, Reducing the water loss and(or) water uptake rate could reducing the water use. Inducing the stomata at high soil water content could reduce the water loss from leaf surface. Lower water uptake rate by decreasing the root hydraulic conductance also reduce the water use and this was association with lower root length density.Experiment 2: 4, Limited water and P deficit significantly reduced shoot and root dry weights(DW) but significantly increased the root to shoot ratio, significantly decreased P concentration in the shoots and roots, P and N accumulation, P and N uptake per root length in the four soybean cultivars at 65 days after sowing(DAS). 5, Flower number and tagged pod number, grain yield, grain number, daily water use significantly reduced but water use efficiency for grain yield significantly increased under drought and P deficits. Applied P significantly grain yield under RWS and this was association with increasing the grain number and(or) grain size(hundred-grain weight). 6, Water and P deficits significantly reduced total root length and root length density(RLD), increased the percent of root distribution at 0-40 cm soil layer but had little effect on adventitious and lateral root density. Among the four soybean cultivars, ZH had significantly higher adventitious and lateral root density in all combinations; ZH had significantly higher adventitious root branching density at P60 under RWS and P0 and P60 under WW. Increasing the percent of root distribution in 0–40 cm soil layer and adventitious and lateral root density increased the P and N uptake per unit root length. 7, Daily water use was positive correlated with RLD but negative correlated with adventitious and lateral root density under RWS. Grain yield was negatively correlated RLD and positively correlated with lateral and adventitious root densities under RWS.In conclusion, reducing the water use in the recent genotypes improved the grain yield and water use efficiency for grain yield under drought. Reducing the water use was association with closing the stomata at high soil water content to restrict the leaf transpiration and lowing root hydraulic conductance. Increasing the P and N uptake per root length by increasing the percent of root distribution at 0-40 cm soil layer, adventitious and lateral root density improved the grain yield under water and P deficits in soybean.