Both water stress and P deficit limit soybean seed yield, but the effects of water regimes and P application rates, their interaction on P status, acquisition, and partitioning, and their roles in yield performance have not been well-studied. Two soybean genotypes (Huangsedadou (HD) and Zhonghuang 30 (ZH)) with contrasting seed yield and root dry weight (DW) were used to investigate the P status, P acquisition, P partitioning, and yield formation under two water regimes (well-watered (WW) and cyclic water stress (WS)) and three P rates (0 (P0), 60 (P60), and 120 (P120) mg P kg−1 dry soil). The results show that increased P and water supply increased the seed yield, shoot and root DW and P concentrations and accumulations in different organs. Cultivar ZH had a significantly higher seed yield than HD at P60 and P120 under WS and at P0 under WW, but a lower seed yield at P60 and P120 under WW. Cultivar ZH had a significantly higher P harvest index and P acquisition efficiency, but a significantly lower shoot and root DW than HD. The interaction between water treatments and P rates had significant effects on leaf and stem P concentration. Cultivar ZH had significantly lower P partitioning to leaves and stems but significantly higher P partitioning to seeds than HD. The seed yield was positively correlated with leaf and seed P accumulations and P acquisition efficiency under WS. We conclude that (1) adequate water supply improved the P mobilization from leaves and stems at maturity, which may have improved the seed yield; and (2) the high P acquisition efficiency is coordination to high P partition to seeds to produce a high seed yield under water- and P-limited conditions.
Complementarity and facilitation with respect to P acquisition do not drive overyielding by intercropping
