Spatial pattern and scale of leaf N and P concentration in a Quercus robur population

Abstract

Although there are numerous descriptions of the spatial variability of nutrients in soil at relevant scales for individuals of a plant population, there are no studies relating this spatial structure with nutrient concentration in plant tissues. The aim of our study was to describe by geostatistical techniques the spatial variability in leaf nitrogen (N) and phosphorus (P) concentrations in a population of young Quercus robur L. growing under a pine canopy, and to examine their relationship with the spatial variability of N and P availability indices in soil. Samples of oak leaves were obtained from 125 individuals previously mapped in an area of 120 m × 120 m. Four soil samples were obtained under each individual. Leaf N, leaf P, soil N-mineralization rate, soil net nitrification, and soil extractable P were analyzed. Whereas leaf N concentration did not correlate with any soil variable, leaf P concentration and N-to-P ratio correlated significantly with the extractable P concentration. Semivariograms detected spatial dependency in all the study variables, with similar ranges for leaf and soil variables. Examination of the maps of P concentration in leaves and soil indicated a greater probability of finding high values of both variables in the northern part of the study plot. These results demonstrate that spatial dependence is evident in the variations in leaf nutrient concentration between individual members of a population, and that at least for the limiting nutrient there is a spatial coincidence with structures observed in soil. Nevertheless the spatial range of leaf P concentration is higher than for soil P, suggesting the capacity of plants to homogenize the environment by exploiting nutrient-rich patches. The existence of spatial dependence in leaf N and P content can have important consequences for herbivores and nutrient cycling in the ecosystem.