Leaf habit affects the distribution of drought sensitivity but not water transport efficiency in the tropics

Considering the global intensification of aridity in tropical biomes due to climate change, we need to understand what shapes the distribution of drought sensitivity in tropical plants. We conducted a pantropical data synthesis representing 1117 species to test whether xylem-specific hydraulic conductivity (K-S), water potential at leaf turgor loss (psi(TLP)) and water potential at 50% loss of K-S (psi(P50)) varied along climate gradients. The psi(TLP) and psi(P50) increased with climatic moisture only for evergreen species, but K-S did not. Species with high psi(TLP) and psi(P50) values were associated with both dry and wet environments. However, drought-deciduous species showed high psi(TLP) and psi(P50) values regardless of water availability, whereas evergreen species only in wet environments. All three traits showed a weak phylogenetic signal and a short half-life. These results suggest strong environmental controls on trait variance, which in turn is modulated by leaf habit along climatic moisture gradients in the tropics.