Print PageNutrient withdrawal from senescing leaves (foliar nutrient resorption) allows plants to use the same unit of nutrients in multiple iterations of biomass growth, reducing losses of potentially limiting nutrients. Foliar chemistry variation resulting from nutrient resorption can directly affect litter quality and, in turn, regulate decomposition rates and soil nutrient availability. Here we investigated patterns of nitrogen (N) and phosphorus (P) resorption in six canopy tree species in a lowland tropical rain forest in Costa Rica. We measured total N and P concentrations in sunlit canopy leaves and species-specific leaf litter collected in littertraps, calculated resorption as the difference between canopy and littertrap leaf nutrient concentrations per unit canopy nutrient, and compared each tree’s bulk leaf litter and topsoil nutrient concentrations to nutrient resorption patterns. We then explored N and P resorption in an Amazon forest regeneration chronosequence where data previously suggested a transition from plant N to P limitation as forests grew back after disturbance. Finally, we put these data into the context of published global resorption datasets to elucidate how resorption relates to ecosystem nutrient status and structure across multiple scales.
Results/Conclusions
In the Costa Rica tropical forest, N and P resorption varied significantly by tree species, and resorption patterns were directly related to species-specific footprints in leaf litter and soil N and P. Species’ leaf litter nutrient concentrations were significantly correlated with canopy leaf, bulk leaf litter and soil nutrients, yet soil and canopy leaf concentrations were not related, suggesting a role for species-specific nutrient resorption (via effects on litter chemistry) in driving small-scale spatial patterns of tropical forest nutrient availability. On average, canopy trees resorbed significantly more P than N (31 vs. 20% resorption, respectively), consistent with previous data suggesting P constraints on ecosystem processes at this site. Patterns in nutrient concentrations across an Amazon forest regeneration chronosequence suggested that, while canopy leaf N:P ratios did not vary systematically with forest age, litterfall N:P changed in concert with other metrics of ecosystem N availability. At larger scales, global nutrient resorption datasets support the notion that N:P resorption ratios are <1 in tropical forests, where P is commonly believed to limit plant growth, and >1 in temperate forests where N is often limiting. Together, these data suggest that, while N and P resorption vary on multiple scales, resorption N:P ratios could offer an alternative foliar metric with which to consider nutrient limitation.
