Drought legacy effects on microbial community structure in a managed grassland

The last decades were characterized by rising temperatures, enhanced atmospheric CO₂ concentrations, and by an increasing frequency of extreme events such as drought. Soil microorganisms are major drivers of biogeochemical processes, yet the effects of climate change in shaping microbial communities remain poorly understood.

To address this knowledge gap, we examined how future climate conditions (combined +300 ppm CO₂ and +3 °C warming, relative to ambient) and drought, alone and in combination, affect microbial community composition throughout the vegetation period in a sub-montane managed grassland (‘ClimGrass’ experiment; Styria, Austria). We combined amplicon sequencing of bacteria, archaea, and fungi with droplet digital PCR to perform quantitative microbiome profiling of seasonal and drought-legacy effects on soil microbial communities.

Drought strongly shaped the bacterial/archaeal and the fungal community structure during peak drought conditions, and this effect could still be detected two and fourteen months after ending drought by rewetting and removing rain-out shelters. In comparison, future climate conditions were observed to exert less pressure on the structure of bacterial/archaeal and fungal communities. Interestingly, abundances of members of Actinobacteria and Bacteroidota for bacteria, as well as Cladosporiaceae and Phaeosphaeriacea for fungi (amongst others) significantly increased during peak drought. Our findings suggest that drought can have immediate and lasting effects on the soil microbial community structure by contributing to the establishment of drought-tolerant microbial communities.