Drought-Driven Divergence in Photosynthetic Performance Between Two Provenances: Insights from Gas Exchange and Chlorophyll Fluorescence Dynamics.

, contributing 25% to China's commercial timber production, faces severe drought threats. However, provenance-specific photosynthetic adaptations remain poorly understood. Here, we compared gas exchange, prompt/delayed fluorescence (PF/DF), and modulated 820-nm reflection (MR) responses of two provenances (JXJJ and FJSM) under different drought treatment times. JXJJ maintained a higher net photosynthetic rate (Pn) and stomatal conductance (Gs) than FJSM under drought stress. The declining rates of F/F, φE, Ψ, δR, PI, TR/CS, and ET/CS were much more rapid in the FJSM than in the JXJJ. An MR kinetics analysis revealed significantly greater PSI impairment in FJSM, evidenced by a 60.2% reduction in P700 re-reduction rate (V) compared to only 44.4% in JXJJ ( < 0.05) at 20 d drought treatment. Similarly, DF measurements demonstrated more pronounced PSII energy transfer disruption in FJSM, with the I/I ratio increasing by 51.3% vs. 43.0% in JXJJ at 20 d drought treatment. These results demonstrate JXJJ's superior drought resilience through coordinated stomatal and non-stomatal regulation. Our findings provide actionable criteria for selecting drought-tolerant provenances, which is essential for sustainable forestry as the climate changes. This study underscores the significance of photosynthetic activity in how responds to drought and gives insights into boosting drought tolerance in forest species through genetic improvements.