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

在第三阶段，SP5将与以前专注于CSP中P循环的SP12合并，形成一个专门从事生物地球化学循环的SP。我们将采用另一种框架来研究基于生产生态学方程(Monteith，1977；Binkley等人，2004)的树木多样性-生产力关系背后的机制：总初级生产=资源供应×资源捕获比例×资源利用效率。因此，我们将量化决定生产力的这三个基本方面，它们与生态系统内的养分循环密切相关。我们假设(A)资源供应(即土壤和生物量中的营养库和通量、凋落物下降、矿化)在很大程度上取决于非生物立地条件、与养分循环相关的植物特征和植物多样性。我们将使用生态景观方法(Z1)中确定的这些参数的基线曲线性能作为当前性能的先验修正因子。(B)捕获资源的比例和(C)资源利用效率高度依赖于乔木和灌木的功能特性和多样性，导致在高多样性与低多样性的情况下更封闭的养分循环。(D)不同物种表现出地上生物量、叶片显示和养分的不同分布，以优化C增益(冠层光合作用的最优化理论)。(E)物种多样性变化引起的资源供应、捕获量和效率的变化不同于立地质量的提高，导致多样性-生产力关系的斜率随着立地质量的增加而变得越来越陡峭。为此，我们量化了以下资源供应的关键方面：(I)森林地面和矿物土壤中有效N、P和阳离子的池(有SP6)；(Ii)通过凋落物产生的凋落物和养分通量(有SP1)；(Iii)矿化(有SP13)。此外，还将确定捕获资源比例的下列方面：(I)乔木、灌木和草本层中的N、P和阳离子(采用SP11)，(Ii)树冠和根系内的生物量和养分分配模式(采用SP1和SP2)。最后，资源利用效率的这些方面将被量化：(I)植物组织中的N、P和阳离子浓度；(Ii)叶片寿命(通过SP3)；叶片衰老期间的叶片养分再吸收效率；(Iv)凋落物中的养分浓度。此外(与SP1和SP2一起)，我们将模拟树木冠层中的光利用，以评估如何有效地利用营养物质进行光合作用。

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.