Various seasonal patterns and potential mechanisms of soil nitrogen transformation along an elevational gradient in the Hengduan Mountains

Abstract Soil nitrogen (N) transformation, a key microbial process in global N cycling, is thought to alter soil N availability and subsequently regulate ecosystem functioning. In particular, the gross rates of N transformation can provide a deeper understanding of internal N dynamics and mechanisms, but questions of whether gross N transformation processes and their underlying drivers change with seasons and elevations remain large uncertain. Based on field collection along an elevational gradient and laboratory incubation experiments, we investigated the seasonal processes of soil N mineralization and nitrification with 15 N isotope dilution technique, and also explored the potential mechanisms involved in the Hengduan Mountains. Unimodal soil gross/net mineralization rates were higher in the wet season (61.32 mg kg −1 day −1 ; 1.01 mg kg −1 day −1 respectively) than in the dry season (10.88 mg kg −1 day −1 ; 0.55 mg kg −1 day −1 respectively) ( p < 0.001), with a peak at medium elevation. Soil gross/net nitrification rates were lower in the wet season (1.43 mg kg −1 day −1 ; −0.017 mg kg −1 day −1 ) than in the dry season (2.49 mg kg −1 day −1 ; 0.004 mg kg −1 day −1 respectively) ( p < 0.001), which increased with increasing elevation. The results detected the dominant drivers of the gross transformation rates, specifically microbial attributes occupied crucial roles in controlling the gross mineralization/nitrification in the wet season, and soil physicochemical properties were dominant controllers on the gross mineralization/nitrification during the dry season. This study revealed the divergent patterns and drivers of N transformation, suggesting that seasonal N cycling should no longer be overlooked if we are to predict N biogeochemical cycles in response to environmental change accurately. Read the free Plain Language Summary for this article on the Journal blog.