Different levels of soil moisture alter the composition but not the diversity of fungal communities

Fungi are an integral part of the soil ecosystem because they assume key roles in decomposition, nutrient cycling, and as plant symbionts. These ecosystem services could be impaired under environmental perturbations such as climate change. Several studies have examined impacts of climate change on fungal communities, yet with no consistent results between surveys. Here we investigated the impact of moisture stress on fungal communities of temperate grassland soils in a seasonal time-scale of almost four months to determine if diversity, community structure, or functional composition is altered. We used Illumina meta-barcoding to characterize the fungal community of a low input meadow near Frankfurt/Main, Germany. In a controlled semi-field experiment, using terrestrial model ecosystems (TME) three treatments of low, high and intermediate moisture were applied over the course of 15 weeks. We found a diverse community of > 3,000 fungal operational taxonomic units (OTUs). Respective community diversity did not change with different experimental soil moisture-levels. However, compositional changes of the community were detectable at the taxonomic level of fungal classes, and OTUs in form of abundance shifts. We identified and functionally assigned 316 OTUs that were significantly responding to either of the moisture conditions. Among these significantly responding OTUs we observed a functional shift: under drought conditions mycorrhizal fungi increased in abundance, while saprobionts decreased. This might indicate that plant-fungal mutualisms buffer the soil ecosystem against environmental perturbations. Overall, the fungal community of the studied grassland seemed largely robust against moisture perturbations, with approximately 10% of the community responding to treatments.