A trait-based approach to unlock the secrets of fungal soil aggregation mechanisms

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Soil aggregation is a major ecosystem process. However, the precise, direct mechanisms leading to soil aggregates and in particular the impact of soil organism traits remain unclear. In the framework of this proposal and the resulting studies, we will unravel the mechanisms of soil aggregation (separately for soil aggregate formation and stabilization) and the impact of functional diversity of saprobic fungi. We will test the three hypotheses that (i) fungal traits contain a phylogenetic signal, (ii) fungal traits determine the ability of fungi to form and stabilize aggregates and (iii) increasing trait distance in pairs of fungi will lead to increased complementarity and thus greater soil aggregation responses. We will test our hypotheses on a set of 30 fungal isolates (saprobic fungi) that were optimized for phylogenetic representation and t-RFLP separation, all isolated from one grassland ecosystem. As a first step, we will gather data for 12 selected traits related to soil aggregate formation and stabilization. These data will be used to evaluate if closely related species have more similar trait combinations than more phylogenetically distant species. In the next step, the 30 isolates will be analyzed for their ability to form and stabilize soil aggregates; these aggregation ability data will be correlated with the corresponding traits to evaluate their importance for the two aggregation processes. In the final step, we will test in pair-wise assembled species combination the impact of trait distance on soil aggregation. The data obtained will shed new light on the mechanisms behind soil aggregation and the role of saprobic fungi in this multidimensional interaction framework; thus we will make an important contribution to soil aggregation research. On the other hand, this project will highlight the usefulness of trait-based approaches with fungi in general.