Complete or overcompensatory thermal acclimation of leaf dark respiration in African tropical trees.

Tropical climates are getting warmer, with pronounced dry periods in large areas. The productivity and climate feedbacks of future tropical forests depend on the ability of trees to acclimate their physiological processes, such as leaf dark respiration (R ), to these new conditions. However, knowledge on this is currently limited due to data scarcity. We studied the impact of growth temperature on R and its dependency on net photosynthesis (A ), leaf nitrogen (N) and phosphorus (P) contents, and leaf mass per unit area (LMA) in 16 early-successional (ES) and late-successional (LS) tropical tree species in multispecies plantations along an elevation gradient (Rwanda TREE project). Moreover, we explored the effect of drought on R in one ES and one LS species. Leaf R at 20°C decreased at warmer sites, regardless if it was expressed per unit leaf area, mass, N or P. This acclimation resulted in an 8% and a 28% decrease in R at prevailing nighttime temperatures in trees at the intermediate and warmest sites, respectively. Moreover, drought reduced R , particularly in the ES species and at the coolest site. Thermal acclimation of R is complete or overcompensatory and independent of changes in leaf nutrients or LMA in African tropical trees.