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My main research interest is in the patterns and processes related to plant diversity. My work is focused on identifying the underlying mechanisms of changes in plant diversity and the consequences of these changes for ecosystem functions, such as productivity, decomposition and pollination. The Wageningen Biodiversity Experiment (WBE, see picture below), which I initiated in 2000 as part of my PhD project and continued until 2011, has been instrumental in this work. Biodiversity experiments like the WBE typically show a positive relation between plant productivity and biodiversity. This pattern has been found repeatedly both aboveground and belowground and is now well established.
What is less established, however, is which mechanisms contribute to this pattern. Initially, potential explanations focused on plant-plant interactions, but empirical evidence for mechanisms such as spatial and temporal resource use partitioning or facilitation is still limited, or restricted to subsets of species (e.g. N-facilitation of grasses by legumes). Currently, we are working on root interactions, to investigate the importance of differentiation in rooting depth for biodiversity-ecosystem functioning relationships (e.g. in the PhD project of Lisette Bakker and projects within the Jena experiment). In addition, we have expanded our scope to plant-pathogen interactions. Research suggests that pathogens cause a decrease in plant biomass production at low plant diversity but not add high diversity, and we are currently working on revealing the underlying mechanism of this pattern (see PhD projects of Eline Ampt and Robert Veldman and the postdoc project of Davide Francioli).
Another major goal is to explicitly link biodiversity-ecosystem functioning to the drivers of changes in biodiversity. One of these drivers is climate change. Elucidating the effects of interactions between biodiversity loss and climate change on ecosystem functioning is a great future challenge, which we take up in two projects: 1) Linking existing biodiversity experiments to climate variability in the STABILITY group funded by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv). The first paper of this group appeared in Nature in autumn 2015, see publications. 2) performing new experiments that manipulate biodiversity and climate change (summer drought) simultaneously (see PhD project Lisette Bakker).