Exogenous application of plant hormones has been considered a short-term and effective strategy to alleviate deleterious effects of water stress on plants. However, whether exogenous gibberellic acid (GA3) directly enhances nitrogen accumulation and thereby alleviates drought stress in soybean (Glycine max (Linn.) Merr.) remains to be investigated. This study set three water treatments (75% CK, 50% MD, 25% SD), with half of the plants at each level sprayed with 10−6 mol·L−1 GA3, measuring growth, photosynthesis, nitrogen content, water status, and electrophysiological parameters and calculating cellular metabolic electronic energy (ΔGB) based on Nernst equation. The results showed that drought reduced soybean nitrogen accumulation, photosynthesis, growth and yield. GA3 increased soybean nitrogen accumulation, improving photosynthesis and yield under CK, which enhanced the consumption of intracellular stored energy and reduced ΔGB. Under MD, GA3 improved leaf water status, promoted soybean nitrogen accumulation and photosynthesis and reduced ΔGB by allocating more energy to drought resistance; it could therefore mitigate the moderate drought stress on plants. ΔGB negatively correlated with total nitrogen content and yield, indicating that ΔGB was a potential indicator associated with nitrogen accumulation, which can guide the optimization of GA3 spraying strategies. Further studies on GA3 application details are necessary to improve the soybean yields under drought conditions.
Xing et al. (Sat,) studied this question.