Fresh carbon (C) input can modify soil C cycling through priming and exogenous C incorporation. Identifying the patterns and drivers of these two processes is essential for understanding C cycling in terrestrial ecosystems. We conducted a laboratory analysis based on 51 soils collected along an elevation gradient to evaluate the magnitude of priming and exogenous C incorporation. The priming effect showed a hump-shaped pattern along the elevation, and the proportion of exogenous C incorporation decreased with elevation. Deep soils had significantly higher priming and exogenous C incorporation than surface soils. The variance in priming effect was negatively controlled by soil initial metabolic quotient (qCO(2)), possibly because of the different microbial energy requirements and consequently, selective utilization of energy-rich or energy-poor substrates. Exogenous C incorporation was negatively correlated with soil qCO(2) and the relative abundance of copiotrophic microorganisms, and positively correlated with soil C saturation deficit. The magnitude of exogenous C incorporation was greater than that of priming, resulting in a net C balance averaging 48.8% of the added exogenous C. Our findings highlight the critical roles of the various microbial properties in regulating soil C cycling under exogenous C input. Considering the above-mentioned factors could improve the performance of C models under changing environments.
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