Resource fluctuations and niche separation in plant communities: Can land-use effects on soil moisture explain observed patterns in plant diversity?

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Plant diversity in grassland systems has been hypothesised Silvertown et al. (1999 Nature) to be related to the plant species' tolerance to drought and water saturated soil, respectively. They argue that drought-tolerant species are particularly sensitive to water-logged soils and vice versa, yielding a drought-water logging-trade off that explains plant diversity. This hydro-ecological hypothesis has as such not been tested independently or experimentally. Here, we propose to use the unique data collected within the Biodiversity Exploratories to test the hydro-ecological hypothesis. Furthermore, we propose to investigate the effect of land use and soil type on hydrological conditions and to test alternative explanations for the hydrological effect (particularly related to soil chemistry). Also, we propose to carry out two manipulative experiments in mesocosms to test the causal link between fluctuating soil moisture and plant diversity, and to disentangle the contribution of nutrient availability and soil moisture. Finally, we propose a pilot study to transfer the hydro-ecological hypothesis to the forest understorey. Here adaptation to shade may trade-off against physiological tolerance of light spots and thus forest floor plant diversity may be similarly explained by differential adaptation to fluctuating resource conditions.