Nitrogen deposition and climate drive plant nitrogen uptake in terrestrial ecosystems

Abstract The role of plants in sequestering atmospheric carbon dioxide is a critical component in mitigating the adverse effects of climate change. A key aspect of this role involves plant nitrogen (N) uptake (Nup) and N use efficiency (NUE), as these factors directly influence the capacity of plants to capture and store carbon. However, the contribution of climatic changes and N inputs remains inadequately understood, introducing significant uncertainties into climate change projections. Here, we used on-the-ground observations across 159 locations to calculate Nup and NUE and identify the main drivers of these processes in natural ecosystems. We found that Nup is primarily driven by abiotic factors, showing an increase with N deposition from anthropogenic activities such as agriculture and combustion, as well as increases in temperature and precipitation. NUE is primarily influenced by biotic factors, showing an increase with the presence of symbiotic ectomycorrhizal fungi and a decrease with microbial nitrogen stocks, likely due to microbial competition for N, and soil pH. In opposition to the classic paradigm in ecology, total soil N stocks were not found to be an important driver of Nup or NUE. A comparison with TRENDY land surface models revealed a potential Nup overestimation by land system models of around 100 Tg N yr-1 in the tropics and tripling the standard deviation on boreal latitudes. Our results underscore the importance of anthropogenic impacts, climate, and microbes as the main drivers of Nup and NUE.