Effects of Combined Extreme Warming and Drought on the Physiology and Growth of Quercus variabilis Blume Seedlings

초록

Climate change is intensifying extreme climatic events such as warming and drought. This study investigated the physiological and growth responses of Quercus variabilis, a major broadleaf plantation species in South Korea, to warming and drought under open-field conditions. From July to August 2024, one-year-old seedlings were exposed to factorial treatments of temperature (ambient: TC; +3 degrees C: T3; +5 degrees C: T5) and precipitation (ambient: PC; drought: DR). Gas exchange was measured twice (early: 12 July; late: 16 August) during the treatment period. In the early phase of the experiment, net photosynthetic rate (P-n) was 11.4% lower in DR than in PC, whereas differences were no longer significant in the late phase. Stomatal conductance (g(s)) was significantly affected by the interaction between temperature and precipitation. These results suggest that the decline in photosynthesis was driven by non-stomatal limitations such as photosystem II impairment or reduced Rubisco activity, despite maintained or enhanced stomatal conductance. Consequently, intrinsic water-use efficiency (iWUE) during the late phase was 24.3% lower in T5 than in TC. Root collar diameter (RCD) was more sensitive to drought than height growth. Shoot (stem + leaf) biomass was 23.7% higher in T5 than in T3, and root biomass was 20.5% higher in T5 than in TC. However, the root-to-shoot (R/S) ratio did not differ significantly among temperature and precipitation treatments. These findings suggest that Q. variabilis seedlings exhibit physiological plasticity and maintain relatively stable biomass allocation under short-term warming and drought conditions.

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