Wider research context: Nutrients are an essential link across trophic levels and networks. Tree diversity has been shown to influence nutrient cycles across trophic levels. However, the complexity inherent in each of the levels and interactions among trophic levels constrain our understanding of tree diversity effects on nutrient cycling that is required to predict the response of forest ecosystems to unprecedented rates of biodiversity loss.
Hypotheses: Here we propose to study the redistribution of nutrients via erosion and the nutrient-related interactions between soil microorganisms (consumers) and plants (primary producers) along the tree diversity gradient of BEF-China. Our central hypotheses are: (1) Erosion redistributes nutrients along slopes and differentiates the nutrient pattern in soils available to soil microorganisms and trees. Eroded parts show lower nutrient availability and foster nutrient recycling while deposition areas are dominated by nutrient overyielding. (2) Soil microorganisms both recycle and take up nutrients more efficiently (‘nutrient overyielding’) in soil of diverse tree mixtures while nutrient overyielding dominates as the underlying process. (3) Trees also both recycle and take up nutrients more efficiently in diverse tree mixtures but recycling is more important. Consequently, the dominance of either one of the processes results in a divergence of stoichiometric responses of trophic levels to tree diversity.
Methods: We will use a stoichiometric approach and assess tree diversity effects on trophic interactions in terms of nutrient cycling. We will combine state-of-the-art runoff-plot based sediment flux measurements, nutrient analyses in soil, plants, and animals and the determination of oxygen isotope signatures in phosphate to reach our aims. In addition, the project will comprise a full soil data baseline (all major nutrients and soil properties) as a courtesy to all projects involved in the research group.
Innovation: We will continue the unique long-term monitoring of soil properties. We will study the influence of tree diversity on lateral matter transport by erosion including the redistribution of nutrients and other aboveground surface components like litter, pollen, plant debris, and organisms, which is a widely neglected mechanism in biodiversity research. Furthermore, we aim to resolve whether higher trophic levels, for example soil microorganisms that consume tree litter, share the same responses to tree diversity as lower trophic levels.