Long-term drought increases soil dark-septate fungi and fungal community turnover, and alters biogeochemical processes in Amazon rain forest

Climate change, regionally driven by deforestation could result in the transformation of evergreen rain forests into seasonal savanna-type vegetation, changing biogeochemical cycles and compromising ecosystem services. Potential future changes in ecosystem carbon and nutrient dynamics in Amazonia were related to the impacts of 14 years of rain exclusion on soil fungal functional diversity and extracellular enzyme activities (EEA). We report increases in fungal diversity in response to drought and striking changes in functional types, with a conspicuous increase in dark-septate fungi, which is likely to be related to water regulation under stressful conditions and thus would enhance ecosystem resilience. Nutrient cycling also changed from an apparent phosphorus and carbon limitation under natural precipitation seasonality to N limitation under experimental drought. The high seasonality of EEA in the control and its remarkable suppression in the drought treatment are an indication of the ecosystem operating at its limits under long-term soil drought.