The Dark Side of Stress Response: Night Temperature Regimes Drive Distinct Abiotic Pathways in Legumes.

Global warming increases night temperatures more strongly than day temperatures. Recent evidence indicates that the effect of night temperature on plant physiology is independent of daytime conditions, suggesting distinct stress tolerance mechanisms. Legume crops, vital to sustainable agriculture, are particularly vulnerable to abiotic stresses, resulting in yield instability. Developing cultivars with round-the-clock stress tolerance requires an understanding of the mechanisms for nighttime abiotic stress tolerance. Unfortunately, data on nighttime abiotic stress response remain limited, particularly for legumes. This review examines the current understanding of nighttime versus daytime abiotic stress response in major crop legumes. Our analysis reveals that high night temperatures primarily affect both pod set and grain weight, while high day temperatures predominantly impact pod set, and low night temperatures mainly reduce grain weight. We explore possible underlying mechanisms, including the balance between photosynthesis and respiration rate, nocturnal stomatal conductance, thylakoid membrane structure and composition, as well as the influence of the circadian clock. Notably, we identify a positive trade-off between warm nights and improved water use efficiency, suggesting promising avenues for breeding climate-resilient legume varieties for the future.