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Single and mixed vegetation types have significant effects on soil parameters and the composition and diversity of soil bacterial community. To understand the influence of different vegetation types on the structure of soil bacterial community across soil depth in a subtropical forest, we assessed the relative abundance of edaphic bacterial community and soil parameters, including pH, cation exchange capacity (CEC), and dissolved organic C in Daiyun Mountain Nature Reserve in Fujian Province, southeastern China. The study area constitutes pine coniferous forest (CF) of Pinus taiwanensis Hayata, broad‐leaved forest (BF) of Castanopsis fabri Hance, and a mixed forest comprising CF and BF (MF). Quantitative polymerase chain reaction (PCR) and Illumina sequencing of 16S ribosomal DNA were used to analyze the abundance, diversity, and composition of soil bacteria. The results showed that the pH, CEC, and diversity of tree species are all associated with the composition of bacterial community in the soil. It was found that CEC, soluble organic N, and pH largely affected the structure of soil bacterial community in A horizon, whereas CEC, moisture content, and organic P affected the structure of soil bacterial community in B horizon. We found that the dominant taxa in the CF and BF were Proteobacteria and Acidobacteria, respectively. The results of both mental and random forest analyses displayed groups according to vegetation types, indicating that the bacterial communities in the research site were significantly influenced by vegetation types in subtropical forests. The study highlights the ecological effects of forest management and elucidates the differences in the functional structure of soil bacterial communities under different vegetation types and soil depths. Core Ideas: Broad‐leaved forests have the highest soil nutrient content in subtropical forests.Acidobacteria and Proteobacteria are biomarker phyla in subtropical forests.Vegetation type affects soil bacterial community structure in subtropical forests.Soil moisture content and organic P affect bacterial community composition in the A horizon.Cation exchange capacity and pH affect bacterial community composition in the B horizon. [ABSTRACT FROM AUTHOR]

Purpose: Dissolved organic matter (DOM) plays an important role in soil C and N cycling. However, the driving mechanisms of DOM concentration and composition under the background of N deposition remains ill-defined. Through experimental N addition, we explored the influence and contribution of microbial community characteristics on DOM concentration and composition. Materials and methods: Field experiments with different N-addition levels were set up in the Daiyunshan Nature Reserve, Fujian, China. Using water extraction and DAX-8 resin separation and phospholipid fatty acids as well as 96-well microplate methods, we mainly probed into the response of DOM concentration and composition, microbial community structure, and extracellular enzyme activity at two soil depths (0–10 and 10–20 cm) to N addition, separately. Furthermore, structural equation models (SEMs) were constructed to explore the effects of microbial community characteristics on the DOM concentration and composition. Results and discussion: The dissolved organic carbon and hydrophilic matter (HIM) decreased significantly with N addition. Moreover, low N addition significantly increased the abundance of gram-negative bacteria and microbial biomass nitrogen, and the activities of urease and cellobiohydrolase in soil. SEMs revealed that the contribution rates of microbial community characteristics to dissolved organic matter (DOM) concentration and HIM were 65% and 60%, respectively. This study focused on the microbial regulation paths for the DOM concentration and composition, including mechanical decomposition, extracellular enzyme secretion, and absorption assimilation. Conclusion: Short-term N addition stimulated microbial communities to regulate soil DOM concentration and composition via three pathways in the subtropical Pinus taiwanensis forest. Under short-term N addition, the absorption and utilization of unstable hydrophilic DOM by microbial communities is the main regulation process, which eventually leads to soil C loss in the form of water-soluble organic C. [ABSTRACT FROM AUTHOR]

Nutrient addition to forest ecosystems significantly influences belowground microbial diversity, community structure, and ecosystem functioning. Nitrogen (N) addition in forests is common in China, especially in the southeast region. However, the influence of N addition on belowground soil microbial community diversity in subtropical forests remains unclear. In May 2018, we randomly selected 12 experimental plots in a Pinus taiwanensis forest within the Daiyun Mountain Nature Reserve, Fujian Province, China, and subjected them to N addition treatments for one year. We investigated the responses of the soil microbial communities and identified the major elements that influenced microbial community composition in the experimental plots. The present study included three N treatments, i.e., the control (CT), low N addition (LN, 40 kg N ha-1 yr-1), and high N addition (HN, 80 kg N ha-1 yr-1), and two depths, 0−10 cm (topsoil) and 10−20 cm (subsoil), which were all sampled in the growing season (May) of 2019. Soil microbial diversity and community composition in the topsoil and subsoil were investigated using high-throughput sequencing of bacterial 16S rDNA genes and fungal internal transcribed spacer sequences. According to our results, 1) soil dissolved organic carbon (DOC) significantly decreased after HN addition, and available nitrogen (AN) significantly declined after LN addition, 2) bacterial α-diversity in the subsoil significantly decreased with HN addition, which was affected significantly by the interaction between N addition and soil layer, and 3) soil DOC, rather than pH, was the dominant environmental factor influencing soil bacterial community composition, while AN and MBN were the best predictors of soil fungal community structure dynamics. Moreover, N addition influence both diversity and community composition of soil bacteria more than those of fungi in the subtropical forests. The results of the present study provide further evidence to support shifts in soil microbial community structure in acidic subtropical forests in response to increasing N deposition. [ABSTRACT FROM AUTHOR]