Drought resistance and post-rewatering recovery of Dendropanax trifidus under elevated CO2 and temperature are mediated by photoprotective regulation and carbon reallocation

Background Drought is expected to become more frequent and severe under climate change, affecting forest structure and carbon sequestration. Tree responses involve multiple physiological and morphological adjustments, but the integrated mechanisms governing drought resistance and post-drought recovery under future climate scenarios remain insufficiently understood. We investigated drought resistance and recovery responses of Dendropanax trifidus seedlings, a warm-temperate species, under three shared socio-economic pathway (SSP) scenarios reflecting elevated CO 2 and temperature by the late twenty-first century. Results During drought exposure, increased absorption flux (ABS/RC) and dissipated energy flux (DI o /RC) per reaction center indicated enhanced photoprotective energy dissipation. Concurrently, decreases in net photosynthetic rate ( P n ) and stomatal conductance ( g s ) showed restricted gas exchange and carbon assimilation, while biomass allocation shifted toward roots to prioritize water acquisition. After rewatering, increased maximum quantum yield of photosystem II ( F v / F m ) and decreased ABS/RC and DI o /RC indicated alleviation of the drought-induced photoprotective state. These changes were accompanied by increases in P n , g s , and aboveground biomass reallocation. Notably, P n failed to return to pre-drought levels under SSP1 but exceeded them under both SSP3 and SSP5, suggesting that scenario-specific environmental conditions influenced photosynthetic recovery. Conclusions These findings suggest that D. trifidus drought resistance depends primarily on photosystem protection, reduced water loss, and root-centered resource allocation, rather than maintaining photosynthetic carbon gain. Post-rewatering recovery involves alleviating photoprotective regulation, restoring gas exchange and carbon assimilation, and shifting biomass allocation toward aboveground organs.