Foliar P- but not N resorption efficiency depends on the P-concentration and the N:P ratio in trees of temperate forests

Abstract

While there is evidence that foliar P concentration controls foliar P resorption efficiency, this is not found for N. Likewise, the foliar N:P ratio affects P, but not N resorption. This study focuses on foliar nutrient resorption efficiency, which describes the proportion of foliar nutrients that is resorbed before abscission. The two main tree types of temperate forests—deciduous and coniferous—are compared in this context. The aim of this meta-analysis is to describe the foliar resorption efficiency of N and P as a function of absolute and relative concentrations of these nutrients in mature foliage, which may serve as a proxy for the plants nutritional status. In addition to prior work on this subject which has focused mainly on single-nutrient resorption efficiency, the effects of relative- and absolute foliar N and P levels are decoupled and analyzed separately. P resorption efficiency was significantly higher at lower absolute foliar P concentration and strongly tied to the original foliar P concentration for both deciduous trees and conifers. In addition, a significant correlation between P resorption efficiency and the foliar N:P ratio was found for deciduous but not for coniferous trees. In contrast, the N resorption efficiency did not relate to the foliar N concentration, nor to the foliar N:P ratio for deciduous and coniferous trees. The results of this study provide strong evidence, that the decoupling of absolute and relative N- and P concentrations in mature foliage is a critical factor for assessing the effect of relative N:P nutrition on nutrient resorption from foliage. If the statistical dependency among absolute and relative foliar N and P concentrations is not considered, the effect of relative N:P nutrition on single nutrient resorption efficiency is likely over-estimated. Overall the results point towards trees of temperate forests being P limited rather than N limited.