Chronic nitrogen addition differentially affects gross nitrogen transformations in alpine and temperate grassland soils

Hao, T. and Zhang, Y. and Zhang, J. and Müller, C. and Li, K. and Zhang, K. and Chu, H. and Stevens, C. and Liu, X. (2020) Chronic nitrogen addition differentially affects gross nitrogen transformations in alpine and temperate grassland soils. Soil Biology and Biochemistry, 149: 107962. ISSN 0038-0717

Text (2._Manuscript_Hao_et_al_clean_version)
2._Manuscript_Hao_et_al_clean_version.pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.
Download (958kB)

Abstract

Nitrogen (N) deposition can profoundly alter soil N cycling of grassland ecosystems. Substrates and soil acidification are expected to modify soil N transformations in response to elevated N deposition. Here, we carried out 15N tracing studies to test the effects of N addition rates (low: 30 kg N ha−1 and high: 90/120 kg N ha−1) and soil acidification on gross N transformation rates using two typical Chinese grassland soils, an alpine calcareous soil and a temperate neutral soil. We found that N addition significantly increased the ratio of gross nitrification rate to gross ammonia immobilization rate (N/I) in both soils, but gross N transformation rates changed differently as a function of N addition rates and soil types. In the calcareous soil, N addition increased soil gross N transformations, largely due to mineral N substrates, SOC, TN and fungal dominance. In contrast, low N addition did not affect gross N transformation rates in the neutral soil, but high N addition significantly decreased gross N transformation rates. Although both SOC and TN were increased with N addition in the neutral soil, N-induced soil pH decline decreased gross N transformation rates. Our results indicate that the effects of N addition on grassland soil gross N transformations are highly dependent on mineral N substrates, SOC and TN. Soil acidification played a more important role than SOC and TN in gross N transformation rate changes in response to elevated N deposition. These findings suggest that the different changes of gross N transformation rates in response to N deposition and soil properties (e.g. SOC, TN and soil pH) should be integrated into biogeochemical models to better predict grassland ecosystem N cycling in the future scenarios of N deposition.