Soil clay minerals: An overlooked mediator of gross N transformations in Regosolic soils of subtropical montane landscapes

Abstract

Soil physiochemical and biological properties have been demonstrated as key controllers of nitrogen (N) transformation in soil; however, the roles of different soil properties in regulating the transformation processes and rates of N remain largely uncertain. Therefore, we quantified the gross transformation rate of N in soil and examined its relationships with N transformation-related functional gene abundances, clay minerals, and soil physiochemical properties across seven Regosolic soils within a subtropical montane agricultural landscape using the 15N tracing approach. We detected substantial variations in gross N mineralization, nitrification, and immobilization rates of NH4+ and NO3− across these Regosolic soils; however, across all soils, the immobilization rate of NH4+ was relatively high to NO3− and the soil's capacity to retain NO3− remained very low. The substantial variation in the gross N transformation in soil was primarily attributed to the influences of microbial functional genes (e.g., bacteria amoA for autotrophic nitrification) and soil properties (e.g., soil pH and sand content for organic N mineralization rates). Moreover, the clay mineral content and soil type regulated rates of gross N transformation processes, including autotrophic nitrification, mineralization, and NH4+ immobilization of Regosolic soils in subtropical montane landscapes. These findings suggest that clay minerals should no longer be overlooked as mediators of gross N transformations in soil.