Drought and rewatering effects on soybean photosynthesis, physiology and yield.

Drought stress is a common environmental stress factor for soybeans ( L.), significantly impeding the growth and yield. Therefore, studying the photosynthetic and physiological characteristics during two crucial growth and development periods, namely the flowering and grain-filling stages, under drought stress and rewatering conditions is of great significance for clarifying the physiological and photosynthetic regulatory response mechanisms of soybeans to drought stress. In this study, the cultivar 'Liaodou 15' was subjected to mild drought (L, 65% field capacity) and severe drought (H, 50% field capacity) treatments during the flowering and grain-filling stages for 7, 14, and 21 days respectively. At the conclusion of the stress period, rewatering (R) was carried out. Results showed that the stomatal limit value increased and intercellular CO concentration decreased with the increase in drought stress intensity, and the decrease in net photosynthetic rate was dominated by stomatal factors at the flowering stage. At the grain-filling stage, the stomatal limit value decreased and intercellular CO concentration increased with the increase in drought stress intensity, and the decrease in net photosynthetic rate changed from stomatal factors to non-stomatal factors. Drought stress led to peroxidation damage. In this study, it significantly increased the contents of soluble protein and malondialdehyde (MDA), as well as the activities of peroxidase (POD) and superoxide dismutase (SOD). On the other hand, rewatering had a compensatory effect on various physiological indices of soybean leaves. Under drought stress, the yield indices of soybeans were affected during both the flowering and grain-filling stages. Specifically, the yield during the flowering stage decreased by 15.63%-55.47%, and the yield during the grain-filling stage decreased by 24.17%-59.63%. This indicates that drought has a greater impact on the yield of soybeans during the grain-filling stage. Moreover, as the duration and intensity of drought increase, the reduction in yield becomes more significant, and the yield is the lowest when there is severe drought stress for 21 days. Our study elucidates the complex physiological and photosynthetic responses of soybeans to drought stress and rewatering, which provides valuable insights for improving soybean cultivation strategies under drought environments.