<b>Organic acids reconfigure microbial carbon-processing potential in biochar-amended Moso bamboo forest soil</b>

Biochar consistently suppressed hydrolytic enzyme activities and increased RubisCO-related activity, shifting the measured functional profile away from decomposition-related activity, while not significantly altering the fungal-to-bacterial gene-copy ratio (F/B) in the no-acid control. In the absence of biochar, all three organic acids increased microbial biomass, cellulose-degradation gene abundances and selected hydrolytic activities at day 14, but did not produce a consistent shift in F/B. In biochar-amended soils, responses became strongly acid- and function-specific.

By day 56, relative to biochar alone, malic acid decreased F/B but increased FPBI, whereas citric acid increased cellulose-degradation gene abundances despite lower cellobiohydrolase activity. By day 56, the organic-acid effect remained significant for FPBI but not for DEAI, indicating that acid effects persisted more clearly in functional-gene potential than in the enzyme-activity profile.</p><p dir="ltr">4. Organic-acid-specific decoupling among fungal-to-bacterial representation, functional-gene potential and enzyme activity indicates that organic-acid chemistry modulates microbial C-processing responses to biochar.</p>