Lithologic control of priming effect in subtropical forest

Lithology is a pivotal factor in controlling soil organic carbon (C) stabilization. The decomposition of soil organic matter can be potentiated by plant C inputs, a phenomenon termed the 'priming effect' (PE), which is a crucial yet highly unpredictable factor in soil C dynamics. However, our understanding of lithology's influence on soil PE remains scant. Here, we quantified soil priming effects in forest soils with different lithology (limestone and clastic rock). Our findings reveal a positive PE intensity in limestone soils, averaging at 0.34 +/- 0.28 mg CO2-C/g SOC. Conversely, clastic rock soils exhibited a negative PE intensity, averaging at -0.38 +/- 0.48 mg CO2-C-1 g SOC. Glucose amendment primed 189.2 % more organic C from the limestone soil than from the clastic rock. Greater PE intensity is associated with higher soil pH, exchangeable calcium/magnesium and lower short-range order iron/aluminum minerals, simple SOC chemical structures, lower iron- and calcium-associated C, dissolved organic C and fungi:bacteria ratio. Additionally, the magnitude and direction of priming effect was negatively correlated with the ratio of fungal to bacterial growth on glucose, and microbial C use efficiency, but correlated positively with total oxidative enzyme activity. Our results provide evidence that priming effects intensity is inherently dependent on lithology, carrying significant implications for refining C cycling models amid changing environmental conditions.