Effekte der Baumdiversität auf die Verfügbarkeit, Aufnahme und Nutzungseffizienz von Nährstoffen in einem subtropischen Baumdiversitätsexperiment

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In the third phase, SP5 will be merged with SP12, which focussed previously on P cycling in the CSPs, to form one SP dedicated to biogeochemical cycling. We will adopt an alternative framework to study mechanisms behind the tree diversity–productivity relationship based on the Production Ecology Equation (Monteith, 1977; Binkley et al., 2004): Gross primary production = resource supply x proportion of resources captured x efficiency of resource use. We will thus quantify these three basic aspects that determine productivity, and which are closely related to nutrient cycling within ecosystems. We hypothesize that (a) resource supply (i.e. nutrient pools and fluxes in soil and biomass, litter fall, mineralisation) is strongly determined by abiotic site conditions, nutrient-cycling related plant traits, and plant diversity. We will use the baseline plot performance of these parameters as determined in the Ecoscape approach (Z1) as a priori correction factors for current performance. (b) The proportion of resources captured and (c) the efficiency of resource use are both highly dependent on tree and shrub functional traits and diversity, resulting in a more closed nutrient cycling at high vs. low diversity. (d) Different species exhibit differential distribution of aboveground biomass, leaf display and nutrients to optimise C gain (optimality theory of canopy photosynthesis). And (e) changes in resource supply, capture and efficiency caused by changes in species diversity are differently affected by increasing site quality leading to increasingly steeper slopes of the diversity-productivity relationship with increasing site quality.For these aims we quantify the following key aspects of resource supply: (i) pools of available N, P and cations in the forest floor and the mineral soil (with SP6); (ii) litter production and nutrient flux via litter fall (with SP1); (iii) mineralisation (with SP13). In addition, the following aspects of the proportion of resources captured will be determined: (i) N, P and cations in trees, shrubs and the herb-layer, both above- and belowground (with SP11), (ii) biomass and nutrient allocation patterns within the canopy and the root system (with SP1 and 2). Finally, these aspects of resource use efficiency will be quantified: (i) N, P and cation concentrations in plant tissues; (ii) leaf longevity (by SP3); leaf nutrient resorption efficiency during leaf senescence; (iv) nutrient concentrations in litter fall. In addition (together with SP1 and 2), we will model light use in the canopy of trees to assess how efficient nutrients are used for photosynthesis.