Fig. 1

Soil microbial carbon use efficiency. Plants primarily input carbon into the soil through root exudates and leaf litter. This litter serves as a carbon source for soil microorganisms, with a portion of the carbon released into the atmosphere through respiratory metabolism. Another portion is assimilated into microbial biomass. Upon death, these microorganisms form microbial residues, which contribute to the accumulation of soil organic carbon. Only a small amount of carbon is consumed for the secretion of extracellular enzymes and metabolic products (negligible). Therefore, microbial carbon use efficiency refers to the ratio of carbon consumed by microorganisms for their own growth to the sum of carbon consumed for both growth and respiration