Long-term mitigation of drought stimulates changes in the forest soil metagenome and alters decomposing microbial communities

Climate change can alter the flow of nutrients and energy through terrestrial ecosystems. Using an inverse climate change field experiment in the central European Alps, we explored how long-term irrigation of a naturally drought-stressed pine forest altered the metabolic potential of the soil microbiome. Drought mitigation by a decade of irrigation stimulated profound changes in the functional capacity encoded in the soil metagenome, revealing alterations in carbon and nitrogen metabolism as well as regulatory processes protecting microorganisms from starvation and desiccation. Despite the structural and functional shifts from oligotrophic to copiotrophic microbial lifestyles under irrigation, degradation of cellulose and lignin was not affected, although different microbial taxa were involved in the degradation as determined by a time-series incubation experiment with 13C-labeled cellulose and lignin. 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 and will help to improve our understanding of alterations in biogeochemical cycling under a changing climate.