Unraveling trees P sources based on the linkage of bottom up und top down approaches for P uptake modelling

有机和无机源对树木吸收磷的贡献仍然没有得到解决。本研究的中心假设是，随着土壤磷储量的减少，有机源对树木的磷营养变得更加重要。我们的测试方法是综合使用自下而上和自上而下的方法来模拟树木对磷的吸收。SPP联合项目为采用这一方法提供了独特的机会。古老的山毛榉林的磷需求将进行评估执行自上而下的建模的基础上的增长数据和凋落物的生产。自下而上的模型将提供潜在的根系吸收的基础上吸收根表面和潜在的供应从矿物和有机源。具体的根长度的评估将结合测量的extramatical菌丝（微）形态学方法，使用反射显微镜。磷动员动力学的分析将在低土壤温度（仅无机磷）和温暖的土壤温度（无机和有机磷）使用薄膜（DGT）中的扩散梯度。然后将数据拟合到动力学过程模型。将通过微透析评估羧酸盐渗出和根系网络协同作用的具体影响以及土壤水分的影响。土壤团聚体的分级将评估与土壤结构相关的磷有效性的变异性。我们的项目的不同工作包将提供相关的知识，在研究地点的过程控制磷的吸收。此外，我们的方法将连接土壤和植物的分析，并将有助于综合多方面的数据有关的P动员和植物吸收的研究地点。我们并不期望一个一致的P-预算的对比森林网站，但实验和不同的模型方法的组合将作为一个框架，其敏感性的输入变量的分类响应P吸收。

The contribution of organic and mineral sources to the P uptake of trees is still unresolved. The hypothesis that organic sources get more important for the P nutrition of trees with decreasing P stocks of soils is in the centre of our project. Our approach of testing this is the integrative use of bottom-up and top-down approaches for the modelling of the P uptake by trees. The joint SPP project provides unique opportunities to follow this approach. Phosphorus requirements of old-grown beech forests will be assessed performing top-down modelling based on growth data and litter production. The bottom-up model will provide the potential uptake of the root system based on the absorbing root surface and the potential supply from mineral and organic sources. The assessment of the specific root length will be combined with the measurement of extramatrical hyphae by (micro)morphological methods using reflecting microscopy. The analyses of P-mobilization kinetics will be performed using diffusive gradients in thin films (DGT) at low soil temperatures (only inorganic P) and warm soil temperature (inorganic and organic P). The data will then be fitted to a kinetic process model. Specific effects by exudation of carboxylates and synergisms of root networks, and the effect of soil moisture will be assessed by microdialysis. Variability of P availability that can be related to soil structure will be assessed by the fractionation of soil aggregates. The different working packages of our project will provide relevant knowledge on the processes controlling P uptake at the study sites. In addition our approach will link soil and plant analyses and will help synthesize manifold data related to P mobilization and plant uptake gained from the study sites. We do not expect a consistent P-budget of the contrasting forest sites, but the experiments and the combination of the different model approaches will serve as a framework for the classification of input variables regarding their sensitivity to the responding P uptake.