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.

Mutualistic associations between plants and arbuscular mycorrhizal (AM) fungi may have profound influences on their response to climate changes. Existing theories evaluate the effects of interdependency and environmental filtering on plant-AM fungal community dynamics separately; however, abrupt environmental changes such as climate extremes can provoke duo-impacts on the metacommunity simultaneously. Here, we experimentally tested the relevance of plant and AM fungal community responses to extreme drought (chronic or intense) in a cold temperate grassland. Irrespective of drought intensities, plant species richness and productivity responses were significantly and positively correlated with AM fungal richness and also served as best predictors of AM fungal community shifts. Notably, the robustness of this community synergism increased with drought intensity, likely reflecting increased community interdependence. Network analysis showed a key role of Glomerales in AM fungal interaction with plants, suggesting specific plant-AM fungal pairing. Thus, community interdependence may underpin climate change impact on plant-AM fungal diversity patterns in grasslands.