Does liming improve microbial carbon use efficiency after maize litter addition in a tropical acidic soil?

Soil pH is one of the main drivers of soil microbial functions, including carbon use efficiency (CUE), the efficiency of microorganisms in converting substrate C into biomass, a key parameter for C sequestration. We evaluated liming effects after maize-litter addition on total CUE (including microbial residues), CUE of microbial biomass (CUEMB), and fungal biomass on an acidic Acrisol with a low C. We established a 6-week incubation experiment to compare limed and unlimed Acrisol treatments and a reference soil, a neighboring Nitisol with optimal pH. Fungal biomass (ergosterol) increased ~ 10 times after litter addition compared with soils without litter, and the final amount was greater in the limed Acrisol than the Nitisol. Litter addition induced a positive priming effect that increased with increasing pH. The increases in soil pH also led to increases in litter-derived CO₂C and decreases in particulate organic matter (POM)C. Thus, in spite of increasing microbial biomass C, CUE decreased with increasing pH and CUEMB was similar across the three soils. CUEMB was positively associated with saprotrophic fungi, implying that fungi are more efficient in incorporating litter-derived C into microbial, especially fungal biomass after 42 days. By including undecomposed maize litter and microbial residues, CUE provided a more comprehensive interpretation of pH and liming effects than CUEMB. Nevertheless, longer-term studies may provide further information on substrate-C turnover and the persistence of liming and pH effects.