Abstract
Water shortage and low phosphorus (P) availability limit yields in soybean. Roots play important roles in water-limited and P-deficient environment, but the underlying mechanisms are largely unknown. In this study we determined the responses of four soybean [Glycine max (L.) Merr.] genotypes [Huandsedadou (HD), Bailudou (BLD), Jindou 21 (J21), and Zhonghuang 30 (ZH)] to three P levels [applied 0 (P0), 60 (P60), and 120 (P120) mg P kg-1 dry soil to the upper 0.4 m of the soil profile] and two water treatment [well-watered (WW) and water-stressed (WS)] with special reference to root morphology and architecture, we compared yield and its components, root morphology and root architecture to find out which variety and/or what kind of root architecture had high grain yield under P and drought stress. The results showed that water stress and low P, respectively, significantly reduced grain yield by 60 and 40%, daily water use by 66 and 31%, P accumulation by 40 and 80%, and N accumulation by 39 and 65%. The cultivar ZH with the lowest daily water use had the highest grain yield at P60 and P120 under drought. Increased root length was positively associated with N and P accumulation in both the WW and WS treatments, but not with grain yield under water and P deficits. However, in the WS treatment, high adventitious and lateral root densities were associated with high N and P uptake per unit root length which in turn was significantly and positively associated with grain yield. Our results suggest that (1) genetic variation of grain yield, daily water use, P and N accumulation, and root morphology and architecture were observed among the soybean cultivars and ZH had the best yield performance under P and water limited conditions; (2) water has a major influence on nutrient uptake and grain yield, while additional P supply can modestly increase yields under drought in some soybean genotypes; (3) while conserved water use plays an important role in grain yield under drought, root traits also contribute to high nutrient uptake efficiency and benefit yield under drought.
Highlights
Soybean [Glycine max (L.) Merr.] is one of the 10 most widely grown crops
Averaging across genotypes and water treatments, shoot and root dry weights increased by 184 and 85%, respectively, and the rootto-shoot ratio (R:S) decreased by 41% with applied P [values are the average of P60 and P120 which did not differ significantly (Figure 1 and Supplementary Table S1)]
Averaging across genotypes and applied P treatments, water stress decreased shoot and root dry weight (DW) by 39 and 21%, respectively, and R:S increased by 13% (Figure 1 and Supplementary Table S1), indicating that more dry matter was partitioned to roots under water stress
Summary
Previous studies have shown that drought stress led to a 24 to 50% reduction in seed yield (Frederick et al, 2001; Sadeghipour and Abbasi, 2012) and P deficit significantly reduced soybean yield (Xu et al, 2003; Jin et al, 2006). Drought (Manavalan et al, 2009) and low phosphorus (P) availability (Schachtman et al, 1998; Xu et al, 2003) are two important factors that limit its yield and yield stability. Drought could restrict the soil P diffusion and P uptake in plants (Suriyagoda et al, 2014). If yields are to be maintained when water and P availability are limited, it is important to understand plant performance and adaptation to moisture- and P-limitations
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