Anaerobic ammonium oxidation (anammox) is the main microbial N loss pathway in alpine wetland soils of the Qinghai-Tibet Plateau

Abstract

Anaerobic ammonium oxidation (anammox) is an important process in the biogeochemical cycle of nitrogen (N). However, knowledge remains limited on the anammox bacterial community, controlling factors, anammox rates and contributions to N loss in alpine wetland ecosystems with low temperatures and deficient oxygen concentrations. This study focused on the distribution, abundance and biodiversity of anammox bacteria and their contribution to N2 production in the rhizosphere and bulk soils of alpine wetlands from the Qinghai-Tibet Plateau along an altitude gradient and discussed their potential relationship with environmental variables. A high diversity of anammox bacteria was found in alpine wetland soils, with most of the detected anammox bacteria classified as unknown species. The anammox bacterial abundance based on the 16S rRNA gene ranged from 1.35 × 103 to 2.52 × 104 copies·g−1 in all the samples, and the anammox process generally contributed 62.66%–88.77% of the N2 production in rhizosphere and bulk soils among the sites at different altitudes, except for the summer bulk soil in Jiuzhi (30.52%) and Maduo (28.84%). The anammox bacterial community was closely linked to the NO2− concentration and water content, while the abundance and activity of anammox bacteria showed a significantly positive correlation with the NO3− concentrations and denitrification rates in both bulk and rhizosphere soils (p < 0.05). These results emphasized the key role of anammox in N cycling in the high-altitude alpine wetlands of Qinghai-Tibet, and extended our understanding of the community dynamics of anammox bacteria and their environmental importance.