Abstract: The depth differentiation in soil carbon dynamics is one of the key factors contributing to the uncertainties in the responses of soil respiration to nitrogen deposition. Analyzing the impact of nitrogen inputs on the vertical differentiation of soil respiration will enhance our understanding of the adaptation mechanisms of soil carbon cycling under global change. We first reviewed the mechanisms underlying soil respiration and changes in atmospheric nitrogen deposition. Then, we examined the effects of both increased and decreased nitrogen deposition on soil respiration at different depths, with a focus on the contribution of nitrogen deposition to soil CO₂ flux in deep soil layer (>30 cm). Microbial nitrogen availability played a key role in regulating deep soil respiration, and nitrogen pool size may drive the response of soil respiration after reduced nitrogen deposition, but the interaction between environmental factors increases its uncertainty. Future research should prioritize exploring the vertical stratification mechanisms of soil respiration and its dynamic thresholds under the situation of reduced nitrogen input, as well as disclosing the interactive effects of multiple factors on carbon-nitrogen-water coupling processes. By integrating source partitioning of respiration components across soil layers and advancing multi-technique approaches, model capability for representing deep carbon turnover can be improved, thereby supporting the accurate assessment of ecosystem carbon budget in the context of global change.

Key words: increased nitrogen deposition, cessation of nitrogen deposition, soil respiration, soil profile, forest ecosystem