Drought tolerance traits explain differential stem growth rates of evergreen and deciduous trees in a tropical karst forest

The karst forest in southwestern China is characterized by thin soil layers, numerous fissures and holes, resulting in low soil water availability and poor water retention, making it challenging for plant growth and survival. While the relationship between plant functional traits and tree growth performance has been extensively studied, the links between tree seasonal growth and drought-tolerant traits in tree species with different leaf habit remains poorly understood. This study evaluated the associations between four-year averaged rainy season stem diameter growth rate and 17 branch and leaf traits across evergreen and deciduous species in a tropical karst forest in southwest China. The cross-species variations in tree growth rates were related to plant hydraulic traits (e.g. vessel lumen diameter, xylem vessel density, stomatal density, and stomatal size) and leaf anatomical traits (e.g. total leaf thickness, lower/upper epidermis thickness, and spongy thickness). The growth of evergreen trees exhibited lower hydraulic efficiency but greater drought tolerance than deciduous tree, which enabled them to maintain higher persistence under low soil water availability and consequently a relatively longer growing season. In contrast, deciduous species showed no correlation between their functional traits and growth rate. The distinct water use strategies of evergreen and deciduous trees may offer a potential explanation for their co-existence in the tropical karst forests.