Differential climate sensitivity of cell anatomy and species-specific hydraulic safety of two Asian tropical pines in Northern Thailand

Abstract

The xylem structure is crucial for mechanical support and hydraulic integrity in trees. However, the impact of climate change on xylem adaptation and hydraulic efficiency in tropical trees in Southeast Asia remains poorly understood. Our study analyzed the seasonal and annual variations in five cell anatomical parameters—lumen diameter (LD), cell diameter (CD), cell wall thickness (CT), number of tracheids (TN), and widths (RW)—as well as three hydraulic parameters—Bending resistance index (BRI), conduit wall reinforcement (CWR), and theoretical hydraulic conductivity (Kh)—in two co-occurring tropical pine species, Pinus kesiya (PIKE) and Pinus latteri (PILA) from 1970 to 2019. We evaluated tree-ring cell anatomy and hydraulic parameters in relation to environmental variables. BRI and CWR were significantly higher for PIKE, indicating better hydraulic safety than PILA across all seasons. We found cellular anatomical parameters of PIKE exhibited significant positive moisture sensitivity and negative temperature/atmospheric drought sensitivity during the dry season and the transition months (March-May). Higher relative humidity during the early-growing season promotes more tracheids with thicker cell walls and wider earlywood in PIKE. The climatic effects are more pronounced on all PIKE parameters than that of PILA, particularly during the latewood phase. Moving correlations revealed the temporal dynamics of climate sensitivity in both pine species, which have become more evident in recent decades due to temperature changes and atmospheric drought. Our findings emphasize the importance of considering species-specific climate sensitivity and tree hydraulic strategies for sustainable forest management and conservation efforts in response to climate change in the Asian tropics.