Urbanization alters land uses and creates heterogeneous environmental conditions in cities and their surroundings, which may directly or indirectly impact soil microorganisms. However, how urbanization affects soil bacterial diversity and community composition, particularly in different land use types, remains largely unknown. In this study, we collected 36 soil samples (18 forest and 18 grass soils) along a rural-suburban-urban gradient in Chang-Zhu-Tan agglomeration. The bacterial diversity and community composition were investigated using 16S rRNA gene sequencing that targeted the V3-V4 region. Our results showed that urbanization induced shifts in bacterial diversity and community composition in both forestlands and grasslands. Specifically, soil bacterial diversity was higher in urban areas than in their suburban and rural counterparts in forests and grasslands, particularly in forests, where significant increases were detected. Urbanization changed the most dominated soil bacterial community from Acidobacteria to Proteobacteria in forestland. Significant decrease and increase were observed in the relative abundance of Acidobacteria (e.g., Acidobacteriales, Acidobacteriia_Subgroup2 and Solibacterales) and Proteobacteria (e.g., Betaproteobacteriales, Myxococcales and Sphingomonadales), respectively, in the forests with increasing urbanization intensity. In contrast, Proteobacteria always dominated the soil bacterial community along the rural-suburban-urban gradient in grassland, and significant decrease and increase in Nitrospirae and Latescibacteria were induced by urbanization, respectively. In addition to urbanization and total nitrogen, total organic carbon and ratio of carbon and nitrogen were the main factors that related with the bacterial community in forest soils, whereas soil water content was the main factor related with soil bacterial community in the grasslands. Together, our results indicate that the urbanization results in shifts in bacterial community composition and diversity, but the extent varied between forest and grassland, which may due to different human management intensity.

Soil food webs are extremely complex as they contain diverse organisms. Feeding preference, also known as prey selection, is an important determinant of soil community compositions. However, the feeding preferences of nematodes are commonly ignored in ecology research. In this paper, the population dynamics and feeding preferences of three bacterial-feeding nematodes (i.e., Caenorhabditis elegans, Protorhabditis spp., and Acrobeloides spp.) for eight bacterial prey species were evaluated. Protorhabditis and Acrobeloides were isolated from a paddy soil in subtropical China. C. elegans, the most common model system for biological research, was used as a control in this study, and it was revealed that C. elegans could feed on all the eight bacteria strains. Protorhabditis could only survive when fed E. coli and Bacillus thuringiensis. Acrobeloides could only survive when fed E. coli and B. aryabhattai. During 10 days of culture, C. elegans populations reached the maximum in 5–7 days, and most C. elegans populations exceeded 10,000 individuals. The two Protorhabditis populations on E. coli and Bacillus thuringiensis included less than 800 individuals during 10 days of culture. Acrobeloides population on B. aryabhattai reached the maximum (7799 individuals) on day 8, while on E. coli was its population included less than 500 individuals. These results indicate that different nematode species indeed have distinct feeding preferences. In addition, the population dynamics of the two soil nematodes isolated from soil could not fully match with their inferred life-history strategies (i.e., cp values, and a 1-5 colonizer-p-ersister series that range from r-strategists to K-strategists). Our findings highlights the existing deficiencies in the understanding of the feeding behavior and the life-history strategies of soil nematodes.

Microbial biomass nitrogen highlights the importance of diverse microbial communities in nutrient cycling and availability. Complex soil food webs improved soil nutrient availability and soybean growth. Soil sterilization boosts soybean growth, likely by eliminating soil-borne pathogens and pests. Soil fertility is one of the key determinants of agricultural productivity. Soil food webs play an important role in driving soil nutrient cycling and plant health. However, it is poorly known how the soil food web composition and complexity affect plant growth and soil fertility. In this study, soil microorganisms and nematodes isolated from two soil types (i.e., calcareous soil and red soil) and two land use types (i.e., corn-soybean cultivation and natural grass-shrubland) were used to sequentially establish four soil micro-food webs (FW1, FW2, FW3, and FW4) with increasing levels of community complexity based on food web complexity. The four micro-food webs were inoculated to sterilized soils which were then planted with soybeans for three months in a pot experiment under ambient environment. The sterilized soil without food web inoculation was employed as control (C) and unsterilized soil with its original food web was also regarded as a treatment (US) in the experiment. The effects of soil micro-food web complexity on soil nutrient and soybean growth were explored. The results showed that soil total nitrogen (TN) and phosphorus (TP), soil microbial biomasses, and plant nitrogen and phosphorus were generally higher in the four food web inoculation treatments than in the control or unsterilized soil. Surprisingly, the original soil food web treatment (i.e., unsterilized soil) had lower soil or soybean nutrient than the no food web treatment (i.e., sterilized soil). In addition, the complexity of inoculated food webs was positively correlated with soil TN, TP, and total potassium (TK). These results suggest that soil micro-food web complexity is an important driver of soil fertility and affects crop growth. Particularly, complex soil micro-food web maintains higher soil fertility and crop growth. This study provides solid evidence of the roles of soil food web in controlling ecosystem services; and the findings could provide a better understanding of the soil food web structure and soil fertility relationships.

Methane (CH₄) emissions are regulated by the balance between CH₄ production and oxidation, which are mediated by methanogens and methanotrophs. Little is known about the key drivers of potential methane production (PMP) under different land use types in the Dongting Lake area. This study investigated four land use types (natural wetland, poplar plantation, rice cropland, and vegetable field) in the Dongting Lake area. The effects of land use types on (a) the abundances and community compositions of soil methanogens and methanotrophs and (b) soil potential methane production were investigated. The results showed that the soil potential methane production of the rice cropland (0.26 ± 0.02 µg g⁻¹ h⁻¹) and vegetable field (0.26 ± 0.01 µg g⁻¹ h⁻¹) was higher than that of the poplar plantation (0.16 ± 0.01 µg g⁻¹ h⁻¹). The compositions of methanogenic and methanotrophic communities varied in response to different land uses. The mcrA gene abundance in the rice cropland (0.84 ± 0.05 × 10⁸ copies/g) and vegetable fields (1.23 ± 0.15 × 10⁸ copies g⁻¹) was higher than that in the natural wetland (0.09 ± 0.01 × 10⁸ copies g⁻¹) and poplar plantation (0.08 ± 0.03 × 10⁸ copies g⁻¹). The pmoA gene abundances in the rice cropland (1.65 ± 0.08 × 10⁸ copies g⁻¹) and vegetable fields (1.88 ± 0.32 × 10⁸ copies g⁻¹) were higher than those in the natural wetland (0.16 ± 0.02 × 10⁸ copies g⁻¹) and poplar plantation (0.11 ± 0.03 × 10⁸ copies g⁻¹). In addition, both pmoA and mcrA gene abundances were positively correlated with potential methane production. However, the regression line between pmoA gene abundance and potential methane production showed a shallower slope than that between mcrA gene abundance and potential methane production. These results suggest that soil potential methane production was primarily driven by increased methanogenesis rather than reduced methane oxidation. In addition, soil organic carbon, total nitrogen, water content, and pH were key abiotic factors regulating potential methane production and the abundance and community compositions of methanogens and methanotrophs in the Dongting Lake area.