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

Drought is a critical constraint for Mediterranean agriculture that significantly affects soil carbon (C) fluxes and microbial dynamics. This study evaluated the influence of tillage (traditional (TT) vs. reduced (RT)) and fertilization (mineral (MF) vs. biosolid compost (BC)) on C mineralization during drying-rewetting cycles (5% to 60% field capacity (FC)). RT treatment exhibited 41% higher soil respiration during drying and a 32% stronger Birch effect post-rewetting compared to TT. This enhanced mineralization was linked to higher Water-Soluble Carbon (WSC) levels. BC amendment improved N-NO 3 − availability and increased microbial biomass carbon (MBC). Soil moisture was the primary driver of microbial assembly, overriding the effects of management practices. Extreme drought (5% FC) acted as an environmental filter favoring xerotolerant taxa like Proteobacteria and Acidobacteriota, while rewetting triggered the rapid proliferation of resistant taxa like Firmicutes. Contrary to one of our hypothesis, the combination of reduced tillage and biosolid compost (RT.BC) unexpectedly amplified rather than attenuated the Birch effect, demonstrating that while soil moisture dictates microbial structure, these management practices intensely modulate carbon mineralization dynamics under Mediterranean drought conditions.