Foliar macronutrient concentrations of forest understorey species in relation to Ellenberg's indices and potential relative growth rate

In order to investigate broad patterns of variation of the foliar mineral nutrient concentrations of herbaceous plant communities in the ground layer of W Europe forests, correlations were examined between Ellenberg's indices (N-index: mineral nitrogen availability, R-index: pH, F-index: soil moisture and L-index: light intensity) and literature values of macronutrient concentrations for 84 forbs and 39 graminoid species. Significant, positive correlations were found between the R-index and the plants' concentration of Ca and K (forbs only) and between the N-index and the plants' concentration of K, P (forbs only) and N (forbs and graminoids). Multiple regressions showed that the N-index was the best predictor of the plants' concentration of N (forbs and graminoids), P (forbs) and Ca (graminoids) and the R-index of the plants' concentration of Ca and K (forbs). The mineral nutrient concentrations of graminoids were lower and less strongly correlated with Ellenberg's indices than those of forbs. It is argued that the mineral nutrient concentrations in the plants match the availability of mineral nutrients in the soil for N, P (N-index) and Ca (R-index), but not for K and Mg. Significant, positive correlations were found between potential relative growth rate and the concentration of some elements (N, P, K and Ca in forbs, Ca and Mg in graminoids). This suggests that the increase in the concentration of these elements in plants along fertility gradients is due, at least partly, to genetically controlled alterations of leaf anatomy associated with increasing potential relative growth rate.