Higher phylogenetic diversity prevents loss of functional diversity caused by successive drying and rewetting cycles.

Microbial communities regulate nutrient cycling in soil, thus the impact of climate change on the structure and function of these communities can cause an imbalance of nutrients in the environment. Structural and functional changes of soil bacterial communities in two contrasting biomes in Brazil, the Atlantic Forest and the Tropical Dry Forest (Caatinga), were studied by simulating, in microcosms, rainfall and drought events. Soil samples were collected in three Brazilian states: Bahia, Pernambuco and São Paulo, in a total of four sampling sites. Analysis of 16S rRNA amplicon libraries revealed changes in microbial communities after three drying-rewetting cycles (60-30% water holding capacity). Alpha diversity indexes were obtained for bacterial communities, as well as the functional diversity index (Shannon) based on the activity of the following enzymes: acid and alkaline phosphatase, arylsulfatase, dehydrogenase, cellulase, amylase, urease and phytase. In general, the soils of Caatinga showed a decrease in the diversity indexes studied, conversely, however, the soils of Atlantic Forest were found to be more resistant during the drying-rewetting cycles. Functional diversity was significantly different for the two biomes, with a decrease in Caatinga soils, while Atlantic Forest samples demonstrated a greater stability of enzymatic activity. Further, the Atlantic Forest samples showed more resistance when compared to samples from Caatinga. The results found in this study have confirmed the hypothesis that biomes, independent of climate, when subjected to successive events of drought and rewetting exhibit structural and metabolic changes.