Published in:
Journal of Geophysical Research: Biogeosciences, 126 (2021) 5
Language:
English
DOI:
10.1029/2020jg006211
ISSN:
2169-8953;
2169-8961
Origination:
Footnote:
Description:
<jats:title>Abstract</jats:title><jats:p>Elevated reactive nitrogen (N) input could modify soil N transformations, regulating ecosystem functions such as soil N retention and loss. Although multiple hypotheses advocate nonlinear variations in soil N transformations with continuous N input, there still lacks empirical evidences for the responses of soil N transformations to multiple N additions. Here, based on a manipulative N addition experiment and a <jats:sup>15</jats:sup>N pool dilution approach, we explored changes in soil gross N transformations with eight N addition levels and associated mechanisms in a Tibetan alpine steppe. Our results showed that soil gross N mineralization rate (GNM) increased first and then stabilized with increasing N additions. Meanwhile, soil microbial immobilization rate (MIM) exhibited an initially increased and subsequently declined pattern under various N addition levels. In contrast, soil gross nitrification rate (GN) increased linearly across multiple N addition levels. Our results also revealed that variations in GNM were mainly regulated by aboveground vegetation N pool‐induced changes in dissolved organic N content along the N addition gradient. Meanwhile, changes in GN were dominantly modified by soil pH‐induced variations in ammonia‐oxidizing archaea abundance across multiple N addition levels. Additionally, alterations in MIM under various N input levels were primarily controlled by microbial biomass which was regulated by dissolved organic carbon content under low N input and NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>‐N content at high N level, respectively. Overall, patterns and drivers of soil N transformations observed in this study provide valuable benchmark for Earth system models to better predict ecosystem N dynamics under global N‐enrichment scenarios.</jats:p>