Adaptive hydraulic strategies of Pinus tabuliformis to drought across moisture-level slopes in the central Qinling Mountains, China

Abstract

Understanding the response mechanism of tree growth to climate change is essential for predicting future forest dynamics in temperate regions facing significant warming and drying situations. However, the mechanisms by which trees adjust their hydraulic structure, growth and physiology in response to water stress and their effects on radial growth and canopy dynamics across different moisture environments remain poorly understood. We investigate the strategies employed by Pinus tabuliformis on dry and wet slopes of the central Qinling Mountains in China to adapt their xylem to climate variability, using anatomical indicators (theoretical hydraulic conductivity (Kh), cell wall thickness, and conduit wall reinforcement (CWR)), tree-ring width and intrinsic water-use efficiency (iWUE) derived from δ13C analyses. Contrasting drought adjustment strategies were observed on dry and wet slopes. Trees on the drier slope deployed a relatively acquisitive strategy characterized by higher Kh and lower CWR. In contrast, trees on wetter slopes adopted a relatively conservative strategy with lower Kh and higher CWR. Under increasing drought severity, trees demonstrated a rise in iWUE, which has the potential to strengthen the response of hydraulic efficiency and safety indicators to precipitation. Moreover, anatomical structure and iWUE differentially affected tree-ring width and Enhanced Vegetation Index at various growing stages. Increasing iWUE could not prevent a decline in radial growth under unfavorable moisture conditions. These findings offer foundational insights into the physiological mechanisms used by P. tabuliformis to adapt to environmental changes in temperate areas, highlighting the complex interactions among climate, anatomical and physiological indicators, and growth dynamics.