High nitrogen accumulation in alpine forest soils of southeastern
Nitrogen (N) deficiency has been recorded in the top surface of Tibetan
Plateau. However, the variation of soil N availability across the
elevational gradient in alpine forests remains poorly understood. Here,
the elevational patterns and determinants of soil N composition, key N
transformation processes and functional microbes across three typical
mountains on the southeastern Tibetan Plateau were characterized by
multiple techniques. Our results showed that soil total N and ammonium
were markedly enriched in high elevation zones where a stable N release
via mineralization and extremely low net nitrification were observed.
Further, the increasing biological N fixation rates along the elevation
driven by abiotic (i.e., high organic carbon) and biotic (i.e., key
diazotrophic taxa like Bradyrhizobium, Herbaspirillum and Klebsiella)
factors greatly benefited N accumulation at high elevations. Our study
offers new insights into the N dynamics in alpine forests on the Tibetan
Plateau under scenarios of future climate change.