Phosphorus allocation to and resorption from leaves regulate the residence time of phosphorus in aboveground forest biomass on Mount Kinabalu, Borneo

1. The residence time of phosphorus (P) in trees is a consequence of plant adaptation to P deficiency, with longer P residence time on soils with low P availability. P residence time has been studied at the leaf or canopy level but seldom at the whole-tree level. Whereas P residence time at the leaf or canopy level is largely determined by leaf longevity and the resorption of P before leaf abscission, P residence time at the whole-tree level will also be influenced by differences in P allocation to different plant parts because leaves and woody organs have distinct longevities. 2. We estimated the residence time of P in aboveground tree biomass (AGB) as the ratio of P mass (i.e. leaves plus wood) to the annual flux of P via litterfall (i.e. fine litter plus coarse woody debris) for seven tropical rain forests with different soil P availabilities on Mount Kinabalu, Borneo. We analysed the effects of P allocation to and resorption from leaves on P residence time along a soil P gradient. 3. P residence time (2.7–9.8 years) was approximately one fifth of biomass residence time (AGB/annual litterfall mass; 19.8–48.8 years). This was due to a disproportionately greater relative allocation of P to leaves (P mass in leaves/P mass in AGB; 0.11–0.46), which had a smaller fraction of biomass (leaf biomass/AGB; 0.02–0.05) but a shorter longevity (1.0–1.8 years). 4. The relative allocation of P to leaves was often high on low-P soils, and P residence time was expected to be short. By contrast, the resorption rate of P from leaves was also high on low-P soils, which extended P residence time with P deficiency. Consequently, P residence time was nearly constant across the forests. 5. The short residence time of P relative to biomass indicates that P residence time depends largely on relative P allocation among plant organs. Similar P residence times among sites were maintained because greater P allocation to leaves on low-P soils was effectively offset by higher P-resorption efficiency.