Enhanced soil quality and carbon sequestration in urban green spaces through the application of Fe-modified biochar combined with Bacillus clausii

During the process of urbanization, urban green spaces soil experience severe degradation due to human activities, resulting in a significant reduction in nutrient content. This degradation severely hampers the ecological functions of urban green spaces soil. Therefore, it is crucial to investigate and implement effective management measures that can improve the soil quality and enhance soil carbon sequestration in urban green spaces. This study aimed to investigate the effects of different treatments, including Bacillus clausii (BC), biochar (B), Fe-modified biochar (FeB), biochar and Bacillus clausii (BBC), and Fe-modified biochar and Bacillus clausii (FeBBC), on the quality of urban green spaces soil. Additionally, this study investigated the effects of these treatments on soil carbon sequestration, the activity of C-cycling-related enzymes and bacterial communities. The results indicate that individual inoculation of Bacillus clausii is the most effective in improving soil Fe availability. The B and BBC treatments result in higher soil pH, available phosphorus and potassium contents. In comparison to the individual application of FeB and BC, the FeBBC treatment significantly enhances soil alkali-hydro nitrogen content, invertase activity, and aggregate stability (particle size > 0.25 mm), thereby contributing to improved soil quality. Additionally, all biochar treatments exhibit higher soil organic carbon (SOC) and particulate organic carbon (POC) contents, thereby increasing organic carbon sequestration, particularly in the FeBBC treatment. When compared to the individual addition of FeB and BC, the FeBBC treatment promotes the conversion of CO2 into carbonate by carbonic anhydrase, thereby augmenting the inorganic carbon content in the soil. Moreover, the FeBBC treatment increases microbial community richness and diversity, improving the composition of carbon cycling-related bacterial communities. This plays a crucial role in maintaining the balance of urban ecosystems. Our results suggest that the FeBBC treatment can be effectively applied as a management measure for urban green spaces soil.