Prolonged water limitation shifts the soil microbiome from copiotrophic to oligotrophic lifestyles in Scots pine mesocosms

Reductions in soil moisture due to prolonged episodes of drought have the potential to affect the whole ecosystem , including soil microbes and their functions. We used a mesocosm experiment with Scots pine saplings and natural forest soil maintained at different soil water contents for two years to assess how the composition of soil microbial communities is affected during prolonged episodes of water limitation and how changes are related to alterations in plant development and soil properties. We combined analyses of multiple physicochemical soil properties and tree parameters with DNA metabarcoding. Prolonged water limitation induced continuous changes in soil microbial community composition. The dissimilarity between prokaryotic communities at different levels of water limitation increased over time regardless of seasonality, while fungal communities were less affected by prolonged water limitation. Under low soil water contents, desiccation-tolerant groups outcompeted less adapted organisms, and the lifestyle of prokaryotic taxa shifted from copiotrophic to oligotrophic. While the abundance of saprotrophic and ligninolytic groups increased alongside an accumulation of dead plant tissues, the abundance of symbiotic and nutrient-cycling taxa decreased, likely impairing the development of the trees. Overall, prolonged episodes of drought appeared to continuously alter the structure of microbial communities, pointing to a potential loss of critical functions provided by the soil microbiome.