SP1: Microbial root symbionts as drivers of eco-evolutionary dynamics and long- term biodiversity–ecosystem functioning relationships in plant communities

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The relationship between biodiversity and ecosystem functioning (BEF) often becomes stronger over time. One mechanism that could explain this observation is a co-adaptation, which develops over time between plants and soil organisms, in particular with arbuscular mycorrhizal fungi (AMF) that live in symbiosis with roots of the vast majority of today’s plant species. Carbon acquisition of AMF strictly depends on plants, which they support by mobilization and transfer of mineral nutrients from soil. Through this interaction, AMF specific to plant species contribute to partitioning of resources among plant communities. However, by forming common mycelial networks, generalist AMF can also facilitate resource sharing. Both mechanisms could contribute to the increase of the BEF relationship over time. Nevertheless, there is a lack of knowledge regarding the dynamics of arbuscular mycorrhizal (AM) symbiosis along plant diversity gradients. In particular, the short- and long-term responses of AMF diversity and community assembly to plant diversity are unclear, as well as the role of these responses in the impact of biodiversity on important AMmediated ecosystem functions. Our subproject explores whether (1) ecosystem aging corresponds to co-adaptation between the fungal and plant partners of AM symbioses, and (2) how this co-adaptation affects AMF specialization and the strength of the symbiotic link. Furthermore, we test (3) whether the contribution of AM symbioses to the BEF relationship is contingent on soil history, plant history, or both. Finally, we investigate (4) whether the observed dynamics are specific to AMF within the soil fungal community and its further functional groups. The subproject will make use of the manipulations of plant diversity in the Jena Experiment, and predominantly, of the experimental treatments, which disentangle time-related co-adaption of plant history and soil history effects. Using molecular methods, we will assess the community structure of AMF in bulk soils and compare it to other fungal communities. In addition, symbiotic community structure, specialization of AMF and mycorrhization intensity will be determined using rhizosphere and roots of resident plant species, both in the Field Experiment and the Ecotron Experiment. Taken together, this subproject aims to elucidate whether the interplay between plant- and AMF diversity changes over time, and whether the resultant AM symbioses play a role in the strengthening BEF relationship over time. In addition, we will assess whether due to their high dependency on plants, AMF behave differently than other fungal groups in the soil that may be less plant species-specific, such as saprotrophs or parasites.