The upper temperature limits of leaf function in tropical trees from a wet tropical forest

Abstract

With the increase in high temperature incidences due to global warming, it has become very important to understand the thermotolerance of plant species. In this study, the thermotolerance and leaf traits of 41 forest species and 14 agroforestry species from a wet tropical forest in the central Western Ghats were measured and their thermal time constants and leaf temperatures calculated. The thermal time constant, 𝜏, determines a leaf’s resistance to external environmental fluxes and the leaf temperature (Tleaf) is an estimate of the temperature a leaf actually experiences in a given ambient temperature. Around half of the measured species showed a negative thermal safety margin (difference between thermotolerance limit, T50, and estimated high value for Tleaf) suggesting that these forests are at great risk from warming events and may experience huge losses to biodiversity. Contrary to expectations, the thermotolerance of the plants did not show any relation to any of the functional traits (leaf mass per area, leaf dry matter content), morphological traits (leaf area, effective leaf width, normalised difference in margin complexity and perimeter/area), leaf temperature (Tleaf) or thermal time constant (𝜏). Among the functional traits, LDMC showed stronger negative correlation with Tleaf and 𝜏 than LMA, suggesting that plants with greater carbon investment to their leaves might be at an advantage in future warming events while being less resistant to sudden environmental fluxes. The positive correlation between Tleaf and 𝜏 hints to a trade-off between the ability to maintain leaf temperatures and resistance to sudden environmental changes. Comparison of the thermotolerance of species which occur in both the northern and central Western Ghats did not show any significant difference between their thermotolerance between the two sites.