Distribution and key influential factors of comammox in drained and waterlogged soils of zoige plateau peatland

Peatlands are important carbon and nitrogen reservoirs, playing crucial roles in nitrogen cycling. During microbially-driven nitrogen cycling, nitrous oxide (N₂O, 298 times global warming potential of CO₂) can be emitted, exacerbating global warming. Complete ammonia-oxidizing bacteria (comammox), a newly discovered group of prokaryotes, can independently oxidize ammonia directly to nitrate, bypassing the nitrite stage, and thereby reducing N₂O production associated with the traditional two-step nitrification process. However, information on comammox distribution and its key influential factors in plateau peatlands remains scarce. Thus, this study chose Zoige plateau peatland in China to collect soil samples from different soil types (drained and waterlogged), across different seasons (non-growing and growing), and at various depth (0-100 cm) to assess comammox abundance and community composition. Additionally, soil properties were analyzed and correlated with comammox abundance and community composition to identify the key factors affecting comammox distribution. Comammox abundance varied significantly across soil types, depth, and sampling seasons. Waterlogged soils demonstrated higher comammox abundance than drained soils. In waterlogged soils, comammox abundance showed higher during growing season than non-growing season, while the opposite trend was observed in drained soils. Regardless of soil types, comammox abundance decreased with increasing soil depth. In soils of Zoige plateau peatland, comammox clades A.1, A.2, A.3 and B.1 were identified, with clade B.1 dominating the comammox community. Both Nitrospira sp. CG24A (clade B.1) and Candidatus Nitrospira nitrificans (clade A.1) showed great seasonal variations. Soil properties, including moisture, pH, carbon, and nutrients, collectively influenced comammox abundance and diversity. Among these factors, NH₄⁺-N was the main factor affecting comammox abundance, while moisture primarily drove community distribution. These findings provide valuable insights into comammox distribution, enhancing our understanding of its potential role in mitigating N₂O emissions and thus nitrogen cycling in plateau peatland soils.