Nitrogen resorption efficiency in mature trees and seedlings of four tree species co-occurring in a Mediterranean environment

Abstract

Many studies have revealed marked changes in the patterns of nitrogen use along ontogeny in tree species. However, there are no reports of the ontogenetic changes in resorption efficiency, despite the fact that nitrogen resorption from senescing leaves is one of the most important plant mechanisms to conserve and optimize the use of this nutrient. Our objective is to analyze the differences in nitrogen resorption between seedlings and adults and to elucidate which of the leaf traits changing along ontogeny determine these possible differences. Green and senescent leaves were sampled from five seedlings and mature specimens of four tree species. N resorption efficiencies were calculated from the differences between N contents in green and shed leaves collected from the same specimens. Minimum N concentrations in leaf litter were used as an estimation of resorption proficiency. N concentration in green leaves and N resorption efficiency were higher in adult specimens for all species. However, with the exception of Pinus pinea, there were no significant differences in proficiency. Contrary to our expectations, the species studied seem to have a lower potential for N resorption during the initial stages of their life cycle. The higher N concentrations seen in adult leaves could explain the higher percentage they are able to withdraw during senescence, probably because they have higher amounts of readily translocatable soluble molecules.