Compensatory Regulation and Temporal Dynamics of Photosynthetic Limitations in Ginkgo Biloba Under Combined Drought–Salt Stress

Photosynthesis in higher plants is highly sensitive to drought and salinity. While studies have examined the individual effects of drought or salt stress on photosynthesis, their combined impact remains poorly understood. In this study, we investigated the diurnal dynamics and primary limiting factors (stomatal, mesophyll, and biochemical) affecting the net photosynthetic rate (An) in Ginkgo (G.) biloba under drought, salt, and combined drought–salt stress. The results revealed that G. biloba exhibited a bimodal pattern of An under control conditions, primarily driven by mesophyll conductance (gm). Under drought, this pattern shifted, with stomatal limitations dominant in the late afternoon. In contrast, salt and combined stress induced a unimodal An pattern due to a flattened gm curve and reduced correlation between gm and An. Interestingly, combined stress caused significantly lower mesophyll limitations than salt stress alone, compensating for increased stomatal limitations and leading to a higher An. Our findings reveal a dynamic shift in the limiting factors over time and stress types, suggesting that G. biloba has mechanisms to mitigate combined drought–salt stress. These insights deepen our understanding of plant resilience under complex environmental conditions.