Scaling the leaf nutrient resorption efficiency: Nitrogen vs phosphorus in global plants

Nutrient resorption from senescent leaves is one essential plant nutrient strategy. Allocation of nitrogen (N) and phosphorus (P) reflects the influences of evolution and ecological processes on plant functional traits, and thus is related to functional types and environmental factors. However, we know little about the pattern among plant functional types (PFTs) and the driving factors of the allometric relationship of N resorption efficiency (NRE) against P resorption efficiency (PRE) in plant leaves (NRE ~ PRE^b; b, scaling exponent). We compiled N and P resorption data from the literature, including 2541 records, 894 plant species, and 488 sites worldwide, and then explored the allometric relationships between NRE and PRE across different PFTs and environmental factors (i.e. climate and soil nutrients). The scaling exponent for overall species was 0.88, suggesting that plants generally re-absorb P from senesced leaves at a higher rate than N. Among diverse PFTs, the scaling exponents of broadleaved (0.91), deciduous (0.92), non-leguminous (0.88), and woody plants (0.90) were higher than those of coniferous (0.81), evergreen (0.89), leguminous (0.74), and herbaceous plants (0.76), respectively. The scaling exponents increased with increasing latitude and soil nutrient (N and P) availability, and decreased with increasing mean annual temperature. Our results suggest that terrestrial plants utilize P relative to N more effectively through resorbing a higher proportion of P than N from senescent leaves. However, the differential resorption efficiency between N and P may vary among diverse plant types, and displayed a biogeographic pattern at global scale through the plant-environment interactions. These findings can broaden our understanding of the nutrient recycling processes within plants, and help in better prediction of nutrient balance in response to global changes.