Microbial community assembly is influenced by a continuum (actually the trade-off) between deterministic and stochastic processes. An understanding of this ecological continuum is of great significance for drawing inferences about the effects of community assembly processes on microbial community structure and function. Here, we investigated the driving forces of soil microbial community assembly in three different environmental contexts located on subalpine coniferous forests of the Loess Plateau in Shanxi, China. The variation in null deviations and phylogenetic analysis showed that a continuum existed between deterministic and stochastic processes in shaping the microbial community structure, but deterministic processes prevailed. By integrating the results of redundancy analysis (RDA), multiple regression tree (MRT) analysis and correlation analysis, we found that soil organic carbon (SOC) was the main driver of the community structure and diversity patterns. In addition, we also found that SOC had a great influence on the community assembly processes. In conclusion, our results show that deterministic processes always dominated assembly processes in shaping bacterial community structure along the three habitat contexts.

The large-scale construction of photovoltaic (PV) panels causes heterogeneity in environmental factors, such as light, precipitation, and wind speed, which may lead to microhabitat climate changes that may affect ecosystems. In this study, plant–soil–microbial systems in shady and non-shady gaps of PV panels in a solar park in Northern China were investigated. The shading caused by the PV panels significantly affected the alpha diversity of plant and fungal communities (p < 0.05). The compositions of plant and soil microbial (bacteria, fungi, and protists) communities were significantly different between shady and non-shady areas (p < 0.05), and the beta diversity of the plant community was significantly correlated with that of the soil microbial community (p < 0.05). Shading enhanced the complexity of microbial communities by strengthening the associations among soil microbes. Photosynthetically active radiation was the main driving factor in the assembly of aboveground and belowground communities on a small scale, and it indirectly shaped the microbial community through its effects on the plant community. This study highlights the important effects of light on microbial community formation and on the relationships among communities in plant–soil–microbial systems. Thus, the effects of solar park establishment on degraded ecosystems should be considered.

Denitrifiers have been shown to vary in abundance and diversity across the environmental gradients; 6 however, the factors that determine the type and magnitude of the response of the denitrifier communities remain unclear. 7In order to reveal the effects of alkaline mine drainage (AlkMD) on the denitrifier community composition and diversity 8 maintenance mechanism in a tailings reservoir, we examined the diversity patterns and adaptation mechanisms of 9 different denitrifier communities in Shibahe copper tailings water in Zhongtiaoshan, China. The results showed that the 10 α-diversity of Proteobacteria and the nosZ І -bearing denitrifier community in downstream seeping water (SDSW) were 11 the highest, while those in the upstream tailings water (STW1) were the lowest. The highest nirS and nirK-bearing 12 denitrifier community α-diversity were measured in STW1, and the lowest in STW3. The community dissimilarity of the 13 denitrifier communities was strongly correlated with environment parameters, but the factors varied in different groups. 14 The Proteobacteria community was correlated strongly with nitrate (NO 3 -); the nirS and nirK-bearing denitrifier 15 communities were correlated strongly with pH, total carbon (TC), NO 3 and ammonia nitrogen (NH 4 + ), and the 16 nosZ І -bearing denitrifier community was correlated strongly with total organic carbon (TOC), dissolved oxygen (DO), 17 NO 3 -, electroconductibility (EC) and spatial distance (PCNM1). Our results indicated that environmental changes were 18 valuable index reflecting variations in denitrifier community composition in AlkMD. Additionally, the findings in this 19 study are helpful in understanding the relationship between the microbial community composition changes and 20 functional adaptation in different ecosystems. (B. Chai).2 IMPORTANCE Metal mine tailings pond is an important site polluted by heavy metals and nitrogen, and excess 22 nitrogen is mainly removed by microorganisms through denitrification. Although many studies have reported that 23Proteobacteria is the main denitrifying bacteria, and nirS, nirK and nosZ-bearing denitrifiers are three key functional 24 groups in denitrification process. However, less is known of their response to discharge of alkaline copper tailings 25 wastewater (AlkMD). AlkMD exerts an adverse impact on composition and structure of denitrifying bacteria community. 26The change of nitrogen and carbon concentration along the flow direction of wastewater resulted in the change of 27 denitrifying bacteria community diversity pattern, that is to say, environmental filtering force drove the denitrifier 28 community structure in this highly polluted ecosystem. 29

The mechanisms underlying community dynamics, which govern the complicated biogeographical patterns of microbes, have long been a research hotspot in community ecology. However, the mixing of multiple ecological processes and the one-sidedness of analytical methods make it difficult to draw inferences about the community assembly mechanisms. In this study, we investigated the driving forces of the soil microbial community in subalpine coniferous forests of the Loess Plateau in Shanxi, China, by integrating multiple analytical methods. The results of the null model demonstrated that deterministic processes (especially interspecific relationships) were the main driving force of the soil microbial community assembly in this study area, relative to stochastic processes. Based on the results of the net relatedness index (NRI) and nearest taxon index (NTI), we inferred that historical and evolutionary factors, such as climate change and local diversification, may have similar effects on microbial community structure based on the climatic niche conservatism. Based on the results of a functional traits analysis, we found that the effects of ongoing ecological processes on the microbial community assembly varied among sites. Therefore, the functional structures seemed to be more related to ongoing ecological processes, whereas the phylogenetic structures seemed to be more related to historical and evolutionary factors, as well as the tradeoff between deterministic and stochastic processes. The functional and phylogenetic structures were mainly shaped by different ecological processes. By integrating multiple ecological processes, our results provide more details of the mechanisms driving the community assembly