Sex-Specific Seasonal Trajectories of Photosystem II Function During Natural Senescence in Ginkgo biloba Revealed by OJIP Fluorescence Analysis

Dioecious plants often exhibit sex-specific physiological strategies that influence their response to environmental change. However, it is not well understood whether such dimorphism extends to the developmental trajectory of the photosynthetic apparatus during natural senescence. In this study, we compared the seasonal development and decline of photosystem II (PSII) function in naturally grown male and female Ginkgo biloba using non-destructive fast chlorophyll a fluorescence induction kinetics (OJIP) and JIP-test analysis. Sun-exposed, healthy leaves were sampled at approximately 15-day intervals from 18 July to 26 November 2024 [day of year, (DOY 188–332)]. The study monitored chlorophyll content and OJIP-derived parameters, and evaluated sex differences statistically (p < 0.05). Chlorophyll content began to decline after DOY 268 in both sexes, but decreased earlier and more rapidly in males. By DOY 332, male chlorophyll content fell to 1.37% of its level at DOY 268, whereas females retained 9.55%. OJIP fluorescence transient analysis revealed that ΔWoj shifted from negative to positive values after DOY 268 in male plants, accompanied by a sustained increase in the relative variable fluorescence at the J step (Vj). This pattern indicates an earlier and more pronounced acceptor-side limitation of PSII in male plants, associated with accelerated accumulation of QA− and restricted electron transfer from QA− to QB and the plastoquinone (PQ) pool. In addition, male plants showed a clearer donor-side limitation, with a pronounced ΔWok response, suggesting reduced stability of the oxygen-evolving complex (OEC). In contrast, females maintained higher cross-section-based energy fluxes (TR0/CS0, ET0/CS0) and PSI-end acceptor reduction capacity (RE0/CS0), and exhibited a slower decline in integrated performance indices (PI abs, PI total, DF abs). Principal component analysis further suggested that male senescence trajectories were more tightly associated with changes in electron-transport efficiency, whereas females exhibited a more gradual adjustment in energy-flux allocation. Collectively, these results reveal pronounced sexual dimorphism in the PSII–PSI functional decline pathway during natural senescence in G. biloba and provide a physiological basis for understanding sex-specific variation in photosynthetic decline in this species, with potential relevance to broader studies of dioecious plants.