Identification of the key regulators of the soil carbon priming effect: A data synthesis

Abstract

Background and aims

The priming effect (PE) plays a crucial role in soil carbon (C) dynamics and the global C balance, yet its driving factors remain controversial.

Methods

Meta-analysis, boosted regression tree (BRT) model, and linear mixed model (LMM) were applied to investigate the effects of various abiotic factors on the PE.

Results

Recalcitrant substance inputs may induce negative PEs in forest and grassland soils, which may become positive in extremely acidic soils (≤ 5.0). Moreover, PE intensities were higher when soil C/N ratios were below 10 or substrate C/N ratios were below 20. According to the BRT model, substrate C input, SOC content, soil C/N ratio, and soil pH were identified as the primary determinants of the PE, explaining 65% of the total variation (each contributing > 10%). Moreover, substrate C input was positively correlated with PE intensity when the impacts of soil moisture, temperature, pH, C/N ratio, and substrate N/C ratio were separated as random effects in the LMM. The total random effect of soil pH and C/N ratio (39.7%) exceeded the total fixed effect of substrate C input and SOC (38.6%), highlighting their role as key regulators of the PE.

Conclusions

This study offers novel insights into the mechanisms of the PE by shifting the focus from soil microbial processes to the regulatory effects of abiotic factors on soil microbial activity and growth. To quantitively estimate the effects of PEs on soil C dynamics, multivariate models should be employed in future studies.