Isotopic labeling evidence shows faster carbon release from microbial residues than plant litter

Abstract Carbon (C) release from plant and microbial residues is a primary pathway of energy flow from photosynthetic and metabolic biomass to carbon dioxide (CO 2 ) in terrestrial ecosystems. Traditional view show that microbial residue C is more resistant to decompose than plant litter because their smaller particle sizes could be preferentially occluded in microaggregates with less microbial accessibility. However, we still lack a quantitative assessment (i.e. isotopic C labeling) to isolate the progressive release of C fractions from both plant and microbial residues. Here we used a global data set of 117 decomposition experiments that traced the 13 C or 14 C release of isotopically labeled plant and microbial residues to estimate the C release rates and turnover times by using a first-order exponential kinetics model. The average C release rates of crop, grass and tree litter were 7.78, 3.79 and 2.11 yr −1 , which were significantly lower than microbial residues (13.07 yr −1 ). Although C release rates of both plant and microbial residues were positively correlated with site temperature, the mean turnover time of microbial residues was 2–6 times lower than plant litter. We suggest that a constraint in microbial and plant residues leads to a predictable pattern of C release during terrestrial decomposition, which could be included in Earth system models.