RESORPTION EFFICIENCY DECREASES WITH INCREASING GREEN LEAF NUTRIENTS IN A GLOBAL DATA SET

To investigate effects of green-leaf nutrient status on senesced-leaf nutrient concentrations and resorption efficiency, we developed a database of nitrogen (N) and phosphorus (P) concentrations in green and senesced leaves from 92 published studies. We fit power functions (i.e., [nutrient]sen = A [nutrient]grB) separately for N and P. The database encompassed 297 perennial species of different life-forms. Across these divergent species and conditions, a major control on senesced-leaf nutrient concentration was green-leaf nutrient status; nutrient concentrations in senesced leaves were positively associated with green-leaf nutrient concentrations (r2 values from 51% to 84%). Within-species variation as well as species differences contributed to the overall variation in nutrient concentrations. Moreover, N and P resorption efficiency decreased, respectively, with increased N and P green-leaf status; fitted power functions indicated that a disproportionate amount of nutrient remained in senesced leaves of higher green-leaf nutrient status. Functional relationships between nutrient concentrations in senesced and green leaves were indistinguishable for evergreen and deciduous species, but evergreens tended to have lower concentrations in both senesced and green leaves. General relationships (across species and environments) between senesced- and green-leaf nutrient concentrations and broad, intraspecific variation in nutrient concentrations suggest that variation in resorption efficiency and proficiency could be a result (and not necessarily a cause) of species sorting across fertility gradients.