Understanding of the relationship between structural and diversity attributes and biomass is important for plant biodiversity conservation, ecosystem service function enhancement and sustainable development of urban forest ecosystems. In this study, road forest (RF), attached forest (AF) and landscape and relaxation forest (LF) were selected as research objects. We systematically evaluated the diversity attributes and above ground biomass (AGB) at two dimensions of different diameter at breast height (DBH) grades and different tree height grades of urban forests in Changchun, Northeast China. Structural equation modeling (SEM) analyses of the correlation between structure attributes, diversity attributes and biomass among different types of urban forests were carried out. The results showed that species richness (SR) and Shannon–Wiener index (H′) of shrubs were lower than those of trees. Under the DBH grades, H′ in each forest type was highest in the 0–10 m grades and SR was highest in the 10–20 m grades. Under tree height grades, both H′ and SR of each type were at the top of the list. AGB was highest in each forest type under 5–10 m height grades. The relationship between AGB and H′ was better in LF, but with no significant relationships in the other forest types. SEM highlighted that in the overall aspect, the effect of forest type on biomass was mediated by structure and diversity attributes. Particularly in LF, there were direct and indirect effects between structure attributes and biomass mediated by diversity attributes. The improvement of the H′, evenness index (J′) and SR could enhance urban forest services, especially for the biomass and diversity of LF.

The rhizosphere microenvironment is crucial to plant–soil physiological processes. The differences among microbial communities in the rhizosphere and non-rhizosphere peatland topsoil (0–15 cm) and subsoil (15–30 cm) in five plant communities dominated by Carex schmidtii, Chamaedaphne calyculata, Ledum palustre, Betula fruticosa, and Vaccinium uliginosum, as well as non-rhizosphere soil in discontinuous and continuous permafrost regions, were studied. We found that the bacteria and nifH gene abundances in the C. calyculata rhizosphere soil in the discontinuous permafrost region were higher than those in continuous permafrost region, while the nirK and nifH gene abundances in the non-rhizosphere soil of the discontinuous permafrost region were lower than those in the continuous permafrost region. The ratio of bacteria to fungi decreased and that of nirK to nirS increased significantly from the discontinuous to the continuous permafrost region, indicating that permafrost degradation can change soil microbial community composition. Fungal abundance was higher in the rhizosphere than the non-rhizosphere soils, suggesting that plant roots provide a more suitable environment for fungi. Moreover, the abundances of the topsoil bacteria; the fungi; and the nirK, nirS, and nifH genes were higher than those in the subsoil because of the organic matter from plant litter as a source of nutrients. The microbial abundance in the subsoil was also more affected by nutrient availability. To sum up, the microbial abundance varied among the different types of rhizosphere and non-rhizosphere soils, and the carbon and nitrogen cycling processes mediated by soil microorganisms may be greatly altered due to permafrost degradation under climate warming.

Alien plants invasion have become a hot issue in the field of ecology. The invasion of alien plants is usually accompanied by changes in the physical and chemical properties of the soil, the ensuing negative feedback creates a favorable environment for its own growth and expansion. Invasive plans have a strong ability to sequester carbon, which can greatly affect the original local ecological environment. In this study, we selected Rhus typhina, an invasive plant widely used for greening, as the experimental subject and natural growing grassland as the control. The aims were to investigate the effects of different degrees of invasion of R. typhina on soil physicochemical properties and carbon emissions, and to explore the influential factors on carbon emission. The results showed that R. typhina invasion significantly increased soil pH, total nitrogen content, easy extraction of glomalin-related soil protein (EEG) and cumulative CO₂ emissions (CEM). It is worth noting that the CEM increased significantly during the severe invasion by R. typhina. The significant increase in soil NH₄⁺-N content and the decrease in soil NO₃⁻-N content indicate that the soil after the invasion of R. typhina has better uptake of NH₄⁺-N. Temperature and soil moisture content had significant direct effects on CEM, while NH₄⁺-N, NO₃⁻-N, EEG and temperature sensitivity of soil organic carbon mineralization Q₁₀ (30 °C/20 °C) had a direct but non-significant effect on CEM. The above findings suggest that R. typhina can generate positive feedback by influencing the physicochemical properties and CEM of the soil, opening the way for its own expansion, which can be targeted to prevent the destruction of local ecosystems during the introduction of cultivation and subsequent management.

Urban parks, as vital components of urban green infrastructure, can improve urban ecological environments, showcase urban culture, and offer spaces for human recreation and exercise. However, human activities in these parks also produce severe disruption to soil ecosystems. Studying the effects of recreational disturbances on soil properties and microbial communities is crucial for conserving urban biodiversity and maintaining ecosystem services. This study investigated the effects of human recreational disturbances (HRDs) on soil physicochemical properties and bacterial communities in four forest stands (Phellodendron amurense Rupr (Phe amu), Salix matsudana Koidz. (Sal mat), Pinus tabuliformis var. mukdensis (Pin tab), and Picea asperata Mast. (Pie asp)) in Changchun’s South Lake Park. The results showed that HRD significantly reduced soil water content (SWC) and total phosphorus (TP) while increasing soil bulk density (SBD) and pH. Soil organic carbon (SOC) and total nitrogen (TN) increased in Phe amu and Pie asp soils but decreased in Sal mat and Pin tab soils (p < 0.05). Electrical conductivity (EC) changes were inversely related to SOC and TN trends. Dominant bacterial phyla included Actinobacteriota, Proteobacteria, Acidobacteriota, and Chloroflexi. HRD reduced bacterial species richness and diversity by 5.3% and 7.6%, respectively. SWC and SBD were key factors influencing bacterial community dynamics, with SBD affecting Bacteroidota, Proteobacteria, and Myxococcota, and SWC impacting Proteobacteria, Bacteroidota, and Actinobacteriota. These findings provide insights for urban park management, supporting soil microbial diversity and sustainable urban ecosystem development.