Role of inter-specific ectomycorrhizal fungal diversity for forest ecosystem nutrition

本项目的主要目的是表征磷获取和循环生态系统中外生菌根真菌对磷吸收和树木营养的种间多样性。在该项目的第一阶段，研究表明，磷形态的垂直分布在我们研究地点的不同土壤深度表现出不同的模式和浓度。这些结果表明，磷的分布对植被的磷供应机制起决定性作用。在这个更新提案中，我们计划研究磷形态和磷有效性是否以及如何构成真菌群落的分类和功能组成。我们将解决以下假设：(i)真菌群落（腐生或菌根真菌）的功能组成根据土层呈现垂直梯度。结果表明，不同磷有效度站点的o层功能相似性高于a层。O层细根及其伴生菌根对缺磷地的磷供应和高磷循环起重要作用，而富磷地的A层细根及其伴生菌根促进磷的获取。为了验证这一建议，我们将研究垂直真菌分布（宏基因组分析），并通过土壤交换实验测试功能差异。对于根相关真菌的功能分析，将应用摄磷成像。（ii）磷有效性的变化引起真菌群落的分类和功能变化。这一假设将通过在贫磷和富磷森林立地施用P、N和N × P进行验证。我们预计施氮也会影响菌根群落的磷有效性。（iii）磷的吸收和向寄主的转运受外生菌根真菌的供应和新近的光同化物的调节。为了验证这一假设，将进行环绕实验。

The main goal of this project is to characterize the inter-specific diversity of ectomycorrhizal fungi for P uptake and tree nutrition in P acquiring and recycling ecosystems. In the first phase of this project, it was shown that the vertical distribution of P forms exhibited contrasting patterns and concentrations in different soil depths of our study sites. These findings suggest that the distribution of P is decisive for the mechanism of P supply to the vegetation. In this renewal proposal we plan to study whether and how P forms and P availability structure the taxonomic and functional composition of the fungal communities. We will address the following hypotheses:(i) the functional composition of the fungal communities (saprophytic or mycorrhizal fungi) shows a vertical gradient according to soil layers. We propose that the functional similarity is higher in the O-horizons than in A-horizons of sites with contrasting P availability. Fine roots and their associated mycorrhizas in the O layer are important for P supply at the P poor site leading to high P recycling, whereas those in the A horizon at the P rich site foster P acquisition. To test this suggestion we will study the vertical fungal profiles (metagenome analysis) and test functional differences by soil exchange experiments. For functional analyses of root associated fungi, imaging of P uptake will be applied.(ii) Changes in P availability induce taxonomic and functional changes of the fungal communities. This hypothesis will be tested by application of P, N and N x P in P-poor and P-rich forest sites. We expect that N application also influences P availability with consequence for the mycorrhizal communities.(iii) P uptake and translocation to the host is regulated by the supply of the ectomycorrhizal fungi with recent photo-assimilates. To test this hypothesis, girdling experiments will be conducted.