The rapid increase in reactive nitrogen (N) released into the environment by human activities has notably altered the structure and composition of forest soil microbial communities (SMCs), profoundly impacting the N cycle in terrestrial ecosystems. However, the response of soil microorganisms to nitrogen addition in different seasons is not clear. This study delved into how SMCs in a subtropical region of central Yunnan, China, specifically in an evergreen broad-leaved forest (EBLF), respond to N deposition during both the dry and wet seasons. Through high-throughput sequencing, we assessed the composition and structure of SMCs under varying N addition treatments across seasons, examining their interplay with soil chemical properties, enzyme activities, and community responses. The findings revealed significant outcomes following four years of N addition in the subtropical EBLF: (1) Significant changes were observed due to the interaction between N addition and seasonal changes. Soil pH significantly decreased, indicating increased soil acidification, particularly in the dry season. Increased moisture in the wet season mitigated soil acidification. (2) In the dry season, N addition led to a decrease in microbial richness and diversity. In the wet season, N addition increased microbial richness and diversity, alleviating the downward trend observed in the dry season. (3) N addition significantly impacted the composition of soil bacterial and fungal communities. Dominant fungal genera in the wet season were particularly sensitive to N addition. (4) Seasonal changes and N addition altered soil microbial community structures. Soil chemical properties and enzyme activities significantly influenced the microbial community structure. However, due to differences in soil moisture, the key environmental factors that regulate microbial communities have changed significantly during the dry and wet seasons. This study serves as a foundation for understanding how N deposition impacts SMCs in EBLF ecosystems in subtropical regions, offering valuable insights for the scientific management of forest ecological resources amidst global change trends.

Atmospheric nitrogen deposition has a profound impact on soil nitrogen (N) cycling within terrestrial ecosystems, altering the microbial community structure and composition. To investigate how nitrogen deposition impacts microbial communities across different seasons, this study focused on a mature subtropical Quercus aquifolioides forest. Four nitrogen treatments were applied, and high-throughput sequencing was utilized to analyze soil microbial composition and structure changes during dry and wet seasons. Additionally, the study explored the interactions between soil nutrients, microbial communities, and nitrogen treatments. Following four years of nitrogen supplementation, the results revealed that: (1) Soil chemistry and enzyme activity shifted significantly due to the combined effects of nitrogen addition and seasonal variations. A marked reduction in soil pH indicated substantial acidification, although the wet season’s increased soil moisture mitigated these effects. (2) Fungal richness and diversity were more sensitive to nitrogen addition than bacterial diversity. (3) During the wet season, nitrogen deposition caused notable shifts in soil microbial community composition, with a notable elevation in the relative proportion of the fungal genus Sebacina (↑112.68%) under MN treatment. (4) Nitrogen addition affected the co-occurrence network complexity of soil bacteria and fungi in a season-dependent manner. During the dry season, bacterial network complexity decreased significantly while fungal network complexity increased. In contrast, the wet season showed an elevation in bacterial network complexity and a reduction in fungal network complexity. (5) The fungal community structure remained stable across seasons and nitrogen treatments, whereas the bacterial community structure showed significant differences after nitrogen addition. Environmental factors influencing bacterial and fungal community structures varied depending on water conditions. These findings provide insights into forest soil management and microbial remediation strategies in response to future atmospheric nitrogen deposition.

Soil microbial communities contribute to the growth, health, and productivity of crops during agricultural production, and yet it is not clear how different fertilization practices affect the diversity, composition, and co-occurrence network of soil bacterial communities at different stages of growing tobacco. Here, we report the characteristics of changes in soil bacterial communities at different tobacco growth stages and fallow periods after fertilizer application by selecting long-term continuous crop tobacco fields with different fertilizers (control (CK), a cattle manure organic fertilizer (OM), a cattle manure organic fertilizer and chemical fertilizer mix (MNPK), a chemical fertilizer (NPK), and crushed straw (ST)) at the time of tobacco planting, combined with high-throughput sequencing technology and molecular ecological network methods. The results showed that soil bacterial diversity did not respond significantly to fertilizer application during the growing period of roasted tobacco, which only increased bacterial diversity in the fallow period. The key taxa of the co-occurrence network were lost during the peak and maturity periods of tobacco cultivation and were gradually recovered after fallowing. The choice of straw, chemical fertilizer, and cow manure organic fertilizer mixed with chemical fertilizer when planting tobacco can better feed the growth of roasted tobacco, and the choice of an organic matter fertilizer (straw and cow manure) as the base fertilizer can accelerate the repair of the bacterial co-occurrence network after the soil has been fallowed and improve the subhealth of the planted tobacco soil.