Advances on microbial mechanisms of nitrogen transformation during nitrification and denitrification at soil aggregates scale

Soil aggregate is a basic structural unit of soil, consisting of primary particles (sand, silt, clay), cementing materials and pores. Specific and independent microhabitats composed of soil aggregates of different particle sizes are biochemical reactors for soil nitrogen transformation. Differences in the physical and chemical properties of microhabitats lead to different microbial differentiation characteristics, which further influence key processes of the nitrogen cycle. The fixation and transformation of nitrogen is carried out by large, small and micro-aggregates together. However, the relative contribution of aggregates of different particle sizes to the key process of the nitrogen cycle is not clear, nor is the interception and retention of different forms of nitrogen. This paper reviews studies on nitrogen transformation during nitrification and denitrification at the soil aggregate scale. We summarize recent advances in aggregate-microbe interactions and key nitrogen cycling processes within aggregates, with emphasis on microbial differentiation patterns. Future research should prioritize two directions: (1) Enhancing the monitoring and quantification of in−situ soil, particularly through ¹⁵N isotope tracing technology to clarify the fate of exogenous nitrogen and plant-microbe competition for nitrogen forms; (2) Development of predictive models for aggregate spatial distribution based on microbial environmental thresholds. These efforts will promote long-term supply and efficient utilization of soil nitrogen, and provide a solid scientific foundation for advancing the theory of micro-scale nitrogen cycling.