The forest soil microbiome in the face of climate change: decomposing soil microbial communities under the influence of water-limitation

Climate change can alter the flow of nutrients and energy through terrestrial ecosystems. In semi-arid environments, limited water availability caused by a combination of high summer temperatures and low rainfall can constrain biogeochemical cycling mediated by the soil microbiome. Using an inverse climate change field experiment in the central European Alps, we explored how long-term irrigation of a long-term drought-stressed pine forest altered the metabolic potential of the soil microbiome and decomposition processes as an important ecosystem function. Drought release by a decade of irrigation stimulated profound changes in the functional capacity encoded in the soil metagenome, showing alterations in carbon and nitrogen metabolism as well as regulatory processes protecting from starvation and desiccation. Despite these structural and functional shifts from oligotrophic to copiotrophic lifestyles under drought release, degradation of cellulose and lignin was not affected, although different microbial taxa were involved in the process as determined by a time-series stable isotope probing incubation experiment. These findings provide new insights into the impact of precipitation changes on the soil microbiome and associated ecosystem functioning in a drought-prone pine forest ecosystem and will help to improve our understanding of alterations in biogeochemical cycling under a changing climate.