Abstract:

Background & Aim：Human activities have substantially altered natural nitrogen (N) regimes, resulting in a marked increase in reactive nitrogen entering terrestrial and aquatic ecosystems. Nitrogen inputs, together with the key ecological processes they drive—such as atmospheric deposition, nitrogen transformation, and changes in nitrogen availability—play a central role in shaping ecosystem structure and functioning. Excess nitrogen inputs disrupt ecological balance through soil acidification, aquatic eutrophication, habitat degradation, and the spread of invasive species, thereby exerting persistent pressure on biodiversity. As biodiversity loss has become a global environmental concern, increasing attention has been directed toward understanding how externally driven nitrogen inputs influence ecological processes most closely linked to species coexistence, community assembly, and ecosystem stability. Rather than treating N inputs driven processes as a closed biogeochemical system, recent studies have emphasized nitrogen inputs as a dominant external driver with direct ecological relevance. At the same time, advances in molecular techniques, remote sensing, and large-scale ecological monitoring have provided new opportunities to examine nitrogen–biodiversity relationships across spatial and organizational scales. 

Progresses：A growing body of evidence demonstrates that the ecological consequences of nitrogen inputs are strongly context dependent. In ecosystems characterized by low background nitrogen availability, moderate nitrogen enrichment may temporarily enhance primary productivity and, in some cases, support short-term increases in local biodiversity. In contrast, sustained or excessive nitrogen inputs are consistently associated with negative biodiversity outcomes, including species loss, community homogenization, and functional simplification. These effects are mediated by multiple interacting processes, such as shifts in soil physicochemical conditions, altered nitrogen availability and stoichiometric balance, and changes in microbially regulated nitrogen transformation pathways. Nitrogen enrichment often favors fast-growing, resource-acquisitive species, intensifying competitive exclusion and reducing niche differentiation, while simultaneously restructuring microbial communities and their functional capacities. Importantly, biodiversity itself can influence nitrogen dynamics. Functional diversity among plants, microorganisms, and soil fauna contributes to more efficient nitrogen use, reduced nitrogen losses, and greater ecosystem resistance to external nitrogen stress. Building on these insights, research on nitrogen inputs and associated ecological processes has increasingly informed biodiversity monitoring, ecological risk assessment, and ecosystem restoration, highlighting the practical relevance of process-oriented nitrogen research. 

Perspectives：Despite substantial progress, significant challenges remain in translating scientific understanding of nitrogen–biodiversity interactions into effective management and policy actions. Data relevant to nitrogen inputs and biodiversity responses are often fragmented across ecosystems, spatial scales, and disciplinary domains, limiting integrative analysis. In addition, monitoring approaches and indicators remain insufficiently standardized, constraining comparisons among regions and long-term assessments. Nitrogen management policies are frequently developed in isolation from biodiversity objectives, reducing the potential for synergistic outcomes. Future research should therefore focus on integrating multi-source datasets, including field observations, molecular information, and remote sensing products, to better capture the dynamics of nitrogen-driven biodiversity change. Developing standardized, process-based monitoring frameworks will be essential for linking nitrogen inputs to biodiversity responses in a policy-relevant manner. Strengthening coordination across sectors—particularly agriculture, environmental management, and biodiversity conservation—will further support the incorporation of nitrogen considerations into governance and decision-making. By adopting a process-informed perspective that explicitly connects nitrogen inputs, key ecological processes, and biodiversity outcomes, research in this field can provide more robust support for ecosystem restoration, adaptive management, and the implementation of the Kunming–Montreal Global Biodiversity Framework.

Key words: biodiversity conservation, nitrogen inputs, key ecological processes, functional diversity, ecosystem stability, ecological restoration