Acid and antibiotic stress suppresses soil microbial carbon use efficiency via fungal proliferation: Mechanistic...

Despite extensive research on environmental implications of acid and antibiotic stresses in soil systems, their effects on the transformation of organic carbon and the soil microbial carbon use efficiency (CUE) remain poorly understood. Here, we used soils from a 36-year field experiment with contrasting fertilization regimes (mineral NPK vs. manure) and conducted microcosm incubations combining ¹⁸O labeling, pH manipulation, and bacterial/fungal inhibition to assess how microbial CUE responds to those stresses. Our results show that CUE declined most strongly under fungal dominance: pH shifts increased the fungal-to-bacterial ratio (F:B) by 142.7 % in manure soils and 228.6 % in NPK soils, while bacterial inhibition induced extreme fungal proliferation and reduced CUE by 57-71 %. Regression analysis revealed an exponential decline of CUE with fungal abundance, whereas microbial diversity and more complex bacterial-fungal networks were positively associated with CUE. Collectively, these findings demonstrate that fungal dominance under acid and bacterial antibiotic stress suppresses microbial carbon efficiency, while biodiversity and cross-domain interactions can buffer such losses, underscoring microbial mechanisms under the stresses of soil acidification and antibiotic contaminations.