Soil carbon fluxes and microbial community responses to drought–rewetting under contrasting tillage and fertilization systems[Dataset]

Drought water stress is a crucial constraint for Mediterranean agriculture, affecting microbial dynamics and soil carbon fluxes. This study evaluated the influence of tillage (traditional -TT- vs. reduced -RT-) and fertilization (mineral -MF- vs. organic biosolid compost -BC-) in a drying-rewetting incubation experiment to quantify the Birch Effect (the pulse of carbon and nitrogen mineralization following the rewetting of a dry soil). Soil samples were subjected to drought and rewetting cycles from 5% to 60% of field capacity (FC). Over these cycles soil respiration, chemical properties related to carbon and nitrogen cycles, and the composition of bacterial and fungal communities were analyzed. RT exhibited higher soil respiration (41% greater during drying) and a maximum CO2 pulse following rewetting (the so-called Birch Effect), linked to a higher concentration of Water-Soluble Carbon (WSC). RT soils also showed faster CO2 stabilization post-rewetting in comparison to TT. The BC amendment significantly improved N-NO3- and increased microbial biomass carbon (MBC). Water stress was the most determinant factor for microbial taxonomic structure, overriding the effect of management. Extreme drought (5% FC) maximized bacterial richness and evenness, acting as a filter that favored xerotolerant taxa like Proteobacteria and Acidobacteriota. Rewetting triggered the rapid proliferation of resistant taxa like Firmicutes. Our results highlight that soil moisture is the primary driver of microbial assembly, while management practices modulate carbon mineralization dynamics under Mediterranean drought conditions.