Seasonal variations in the soil microbiota of a temperate wetland in Northeast China in response to nitrogen deposition

Purpose: China has recently witnessed a significant rise in nitrogen (N) deposition associated with human activities, especially in temperate regions. Although much research has been conducted on aboveground biodiversity, the effects of long-term N deposition on the composition, function and variety of the soil microbiota (especially across seasons) have received less attention. Methods: We investigated the effects of varying levels of nitrogen deposition on the composition, function and diversity of soil microbiota (bacteria and fungi) in temperate natural wetlands in summer and winter using Illumina sequencing. N deposition are categorized into low N addition (LN: 40 kg N/ha yr-1) and high N addition (HN: 80 kg N/ha yr-1). Results: In both summer and winter, N deposition had a significant effect on bacterial alpha diversity. In contrast, fungal alpha diversity exhibited no significant change in either of the two seasons. Additionally, the diversity of the soil microbiota exhibited higher sensitivity to N deposition in winter compared to summer. During the summer months, nitrogen deposition significantly altered the relative abundance of bacterial phyla such as Acidobacteria, Myxococcota, Verrucomicrobia and Actinobacteria. In winter, bacterial phyla in the surface soil exhibited distinct changes in their relative abundance. Relative abundance of Epsilonbacteraeota was highest in plots without added nitrogen, whereas the N-treated plots exhibited the lowest abundances. In addition, the relative abundance of Ascomycota was significantly increased by the addition of N, whereas Mortierellomycota exhibited a significant decrease, with Basidiomycota exhibiting no significant effect. The results from the structural equation model (SEM) revealed that soil organic carbon (SOC) and total nitrogen (TN) exerted a significant influence on the composition of both bacterial and fungal communities in the soil, regardless of the season. Specifically, in the summer season, SOC and TN account for 87 % of the variation observed in bacterial diversity and 83 % of the variation in fungal diversity. Likewise, during the winter season, these factors explain 91 % of the changes in bacterial diversity and 88 % of the changes in fungal diversity. Conclusion: Our research findings have unveiled that bacterial communities display a heightened sensitivity to nitrogen (N) deposition compared to their fungal counterparts. This discovery emphasizes the crucial need to concurrently evaluate the responses of the soil microbiome to global changes across various seasons, highlighting the intricate interplay between microbial dynamics and environmental factors.