Ammonia‐oxidizing bacteria rather than ammonia‐oxidizing archaea dominates soil nitrification during vegetation restoration in karst areas

Abstract Soil nitrification, driven by ammonia‐oxidizing archaea (AOA) and ammonia‐oxidizing bacteria (AOB), is a crucial process in maintaining the soil nitrogen (N) balance. However, the influence of AOA and AOB on soil gross nitrification rates (GNR) in response to vegetation restoration remains unclear, particularly in karst regions. In this study, we investigated soil GNR and the abundance, diversity, and community composition of AOA and AOB across after vegetation restoration. Four land use types were examined: plantation forest (PF), forage grass (FG), a combination of plantation forest and forage grass (FG), and cropland (CR, control). Soil ammonium N () was higher in the vegetation restoration compared to that in cropland, whereas nitrate N () exhibited the opposite trend. Soil GNR were reduced by 55.4%–90.3% in the vegetation restorations compared to that in cropland. The abundance, Chao1, and Shannon index of AOB were lower in vegetation restorations compared to cropland, respectively. The abundance and diversity of AOA were higher than those of AOB but were unaffected by vegetative restoration. Furthermore, AOB community is more sensitive to vegetation restoration than AOA community. Specifically, the abundance of AOB taxa belonging to the genera Nitrosospira and Nitrosovibrio was decreased by the restoration efforts. In addition, soil nutrients availability (e.g., , , and phosphorus) and AOB index (e.g., Shannon index) were the main factors driving soil GNR. This study highlights the importance of AOB in driving soil nitrification during vegetation restoration and emphasizes the necessity to optimize soil nitrogen management in karst ecosystems.