Enhanced priming effect in agricultural soils driven by high-quality exogenous organic carbon additions: A meta-analysis

The addition of exogenous organic carbon (C) to soil can either accelerate or retard the soil organic carbon (SOC) mineralization, i.e., the priming effect (PE), which plays a crucial role in SOC sequestration and thus is significant in the context of global warming. However, the influence of exogenous organic C quality on PE remains poorly understood, potentially limiting our understanding of SOC dynamics. Thus, we conducted a global meta-analysis to reveal the effect of exogenous organic C quality on PE through compiling a data set of 2031 experiment trials. Our results revealed that the addition of organic C significantly enhanced SOC decomposition by 46.23 % in agricultural soils. Labile C compounds induced a stronger PE than both intermediate and recalcitrant C compounds. Organic C materials rich in labile C compounds or with low lignin/N ratios exhibited a greater PE than the resistant substrates. Notably, a threshold C/N ratio of 25 was associated with a higher PE in substrates with C/N < 25. Given the pronounced PE observed with high-quality organic C addition (characterized by C/N <25, low lignin/N ratio, and easy decomposability), we proposed that "stoichiometric decomposition" might predominate the PE in agricultural soils. Collectively, the current study underscores the significant role of exogenous organic C quality in modulating the PE, emphasizing the need for further research to inform effective SOC management strategies.