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

<i>Cunninghamia lanceolata</i>, 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_V/F_M, φE_O, Ψ_O, δR_O, PI_ABS, TR_O/CS_M, and ET_O/CS_M 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_red) compared to only 44.4% in JXJJ (<i>p</i> < 0.05) at 20 d drought treatment. Similarly, DF measurements demonstrated more pronounced PSII energy transfer disruption in FJSM, with the I₂/I₁ 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 <i>C. lanceolata</i> provenances, which is essential for sustainable forestry as the climate changes. This study underscores the significance of photosynthetic activity in how <i>C. lanceolata</i> responds to drought and gives insights into boosting drought tolerance in forest species through genetic improvements.