Plasticity and implications of water-use traits in contrasting tropical tree species under climate change

Plants face a trade-off between hydraulic safety and growth, leading to a range of water-use strategies in different species. However, little is known about such strategies in tropical trees and whether different water-use traits can acclimate to warming. We studied five water-use traits in 20 tropical tree species grown at three different altitudes in Rwanda (RwandaTREE): stomatal conductance (g_s), leaf minimum conductance (g_min), plant hydraulic conductance (K_plant), leaf osmotic potential (ψ_o) and net defoliation during drought. We also explored the links between these traits and growth and mortality data. Late successional (LS) species had low K_plant, g_s and g_min and, thus, low water loss, while low ψ_o helped improve leaf water status during drought. Early successional (ES) species, on the contrary, used more water during both moist and dry conditions and exhibited pronounced drought defoliation. The ES strategy was associated with lower mortality and more pronounced growth enhancement at the warmer sites compared to LS species. While K_plant and g_min showed downward acclimation in warmer climates, ψ_o did not acclimate and g_s measured at prevailing temperature did not change. Due to distinctly different water use strategies between successional groups, ES species may be better equipped for a warmer climate as long as defoliation can bridge drought periods.