Sexual differences in gas exchange and chlorophyll fluorescence of Torreya grandis under drought stress

Torreya grandis seedlings showed significant gender difference under drought stress and females had a better performance in the process of photosynthesis. Starting with saturated moisture content, the natural drought stress process was comprehensively investigated to clarify the possible sex differences of Torreya grandis and how the components of the entire photosynthetic electron chain respond to drought stress. We examined gas exchange, prompt chlorophyll a fluorescence (PF), delayed fluorescence (DF), and modulated 820 nm reflection (MR) in both male and female torreya seedlings that received a drought stress treatment for a total of 20 days. The net photosynthesis (Pn) and stomatal conductance (Gs) of these plants all decreased relative to the corresponding control groups (0 days), and the exchange capacity between primary quinone acceptor (QA) to secondary quinone acceptor (QB) became limited compared to the onset of drought. The oxygen-evolving complex (OEC) was also damaged, and the performance index on an absorption basis (PIABS) was significantly reduced by drought. Drought stress affects either the oxidation of plastocyanin (Pc) and the PSI reaction center (P700) or the re-reduction of Pc+ and P700+ over time. Our results showed that torreya seedlings were inhibited by prolonged drought stress, which significantly reduced their photochemical activities of photosystem II (PSII) and photosystem I (PSI), but PSII was more sensitive than PSI. When the gender differences in gas exchange were compared, females performed better than males under drought. In the aspect of fluorescence curves, female plants also showed a slower rate of damage in PSII and PSI under drought stress than males. Thus, we concluded that female individuals of torreya might possess better adaptability to drought stress than male individuals.