Linking Water and Carbon Use Traits to Drought and Warming Response Strategies in Three High-Elevation Species

Accelerated drought stress along with global warming has significantly impacted high-elevation ecosystems, causing a massive decline of conifers worldwide, including Korean fir (Abies koreana E.H.Wilson). However, studies on the climate adaptability and underlying physiological mechanisms of coexisting species remain limited, despite their importance for understanding future species composition. To investigate species-specific responses to climate change, a rainfall reduction and heat experiment was implemented by blocking precipitation by 33% and 67% and increasing temperature by 1.5°C for three coexisting high-elevation tree species: Korean fir, Korean pine (Pinus koraiensis Siebold & Zucc.), and Manchurian ash (Fraxinus mandshurica Rupr.). Korean fir exhibited the most sensitive stomatal control to conserve its hydraulic status, which significantly suppressed photosynthesis, depleted root starch reserves, and ultimately reduced growth. In contrast, Manchurian ash showed the highest resistance, with stable stomatal response through active leaf osmoregulation and increased chlorophyll content, which supported the maintenance of photosynthesis and root nonstructural carbohydrate (NSC) reserves. Korean pine exhibited intermediate responses, with the second-most sensitive stomatal and photosynthetic regulation, along with temporarily tolerant traits such as increased leaf sugar and chlorophyll content, while allocating relatively more carbon to growth than to storage. This resulted in the highest mortality in Korean fir, followed by Korean pine and Manchurian ash. This study enhances our understanding of the early stress responses of high-elevation species and provides insights into predicting future forest dynamics.