Soil aggregates regulate the impact of soil bacterial and fungal communities, on soil respiration

Soil aggregate size significantly impacts microbial communities and soil respiration. Soil total porosity and pH can regulate the distribution of soil bacteria and fungal communities within aggregates, thereby influencing soil respiration. However, it is unclear how it affects the microbial community composition distributed in soil aggregates, especially for fungal communities. The roles of soil total porosity and pH in controlling the microbial composition of soil aggregates are also unknown. In this study, we used high-throughput sequencing of the 16S rRNA and ITS gene regions to target bacterial and fungal members of aggregate samples of four sizes (2-4 mm, 1-2 mm, 0.25-1 mm and < 0.25 mm). Our results showed that high respiration occurred in soil aggregates of 2-4 mm and 1-2 mm when there was high soil total porosity and low soil pH than in aggregates of 0.25-1 mm and < 0.25 mm. Moreover, soil aggregates of 2-4 mm and 1-2 mm were dominated by four bacterial families (Oxalobacteraceae, Sphingomonadaceae, Cytophagaceae and Genunatimonadaceae) and two fungal families (Lasiosphaeriaceae and Rhizophlyctidaceae), while the 0.25-1 mm and < 0.25 nun aggregates were dominated by two bacterial families (Bacillaceae and Clostridiaceae) and one fungal family (Nectriaceae). Our results suggest that soil organic carbon and total porosity positively influenced the bacterial Shannon index, which led to a further positive influence on soil aggregate respiration, while soil pH positively affected the soil fungal Shannon index, leading to increased negative control of the respiration of soil aggregates.