The effect of tree species diversity on phosphorus availability and cycling

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The maintenance of soil fertility through species diverse forests might be an important ecosystem service in tropical regions with their large areas of forest plantations. Preliminary investigations at the Comparative Study Plots of BEF China have shown, that soil P concentrations are very low, a large proportion of available P is in organic from, and that many of the species show of leaf and litter P concentrations that are indicative P limitation. However, the high variation of P tissue concentrations points to a variety of species-specific mechanisms to adopt to limited P supply. Given the large range of biologically available soil P compounds, and the variety of mechanisms by which plants can access P, we assume that co-existing plant species partition soil organic P to reduce competition. Based on this we hypothesize that (a) the proportion of soil P in available fractions increases with increasing tree species diversity of plots, (b) neighbourhood tree species diversity affects soil P fractions and nutrition of individual trees, and (c) effects of tree species diversity on productivity decline (complementarity reduction) with decreasing diversity of soil organic P sources. In addition, we will explore whether the different soil P fractions can be distinguished on the basis of their spectral properties, which would greatly reduce analytical efforts.