Effects of Drought and Warming on Biomass, Nutrient Allocation, and Oxidative Stress in Abies fabri in Eastern Tibetan Plateau

Abies fabri (Mast.) Craib is an endemic and dominant species in typical subalpine dark coniferous forests distributed in the eastern Tibetan Plateau. To assess how A. fabri may respond and adapt to future climate changes, we investigated the effects of drought and warming on the growth, resource allocation in biomass, membrane stability, and oxidative stress of the seedlings over two growing seasons. Drought (11.4 % average reduction in soil moisture) was created by excluding natural precipitation with a plastic roof and warming was performed by an infrared heater above the plots. Drought increased root length, the root-to-shoot ratio, N concentration, and N/P ratio in all organs, and decreased seedling height and C/N ratio in all organs. Moreover, warming (2 °C) decreased seedling height, root length, total biomass, and N concentration in stems but increased the C/N ratio. Furthermore, the combination of drought and warming decreased seedling height and biomass in all organs, which further increased the N concentration and N/P ratio in all organs. A significant decrease in the membrane stability index and an increase in malondialdehyde, superoxide radical (O₂ ^?), and hydrogen peroxide (H₂O₂) were exactly matched with a dramatic decrease of total biomass under the combination of drought and warming treatment. Together these results implied that drought alone and warming alone were unfavorable for the early growth of A. fabri, and drought plus warming will intensify the opposite effect of drought alone or warming alone. Moreover, N will be a limited nutrient under extant and future climate changes.