Microalgal amendments can improve soil structure by regulating extracellular polymeric substances (EPSs). However, the mechanisms underlying this process in red soils (characterized by high clay content and susceptibility to acidification) under different farming practices remain unclear. This study examined how Chlorella vulgaris (C. vulgaris) amendment influences EPS composition to enhance soil aggregate stability under arable land and rice paddy farming. A five-month pot experiment using a completely randomized design was conducted to investigate the effects of Chlorella vulgaris amendment on soils cultivated with Pennisetum × sinese and rice, two economically important crops commonly grown in South China. At the end of the experiment, Chlorella vulgaris amendment substantially increased both the mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates under both farming systems. Excitation–emission matrix (EEM) fluorescence spectroscopy revealed distinct changes in soil EPS components between the two farming types. Under arable land farming, humic-like and protein-like EPSs were dominant in Chlorella vulgaris-amended treatments, with fluorescence intensities more than doubling compared to the control. Conversely, under rice paddy farming, soil fulvic acid was the main component and showed a moderate increase. Partial least squares path modeling (PLS-PM) demonstrated that protein-like and humic-like EPSs had the strongest direct effects on aggregate stability in arable land red soil, while fulvic acid was the key factor in rice paddy red soil. The present study demonstrates that Chlorella vulgaris amendment improves aggregate stability in red soils through farming-specific, EPS-mediated pathways, providing a quantitative framework for researchers and land managers seeking to apply microalgal amendments for red soil enhancement and sustainable land management.

Remnant forests are vital in urban ecosystems as they serve as a crucial link between organisms, inorganic environments, and human settlements. However, there is a lack of research on how urbanization affects the physical and chemical properties of soil in remnant forests, as well as the response of soil fauna to environmental changes within these forests. Our study utilized the urbanization gradient research method to investigate the characteristics of the soil fauna community in remnant forests across different urbanization gradients and to understand its intrinsic response to environmental changes. Our results indicate support for the “moderate disturbance hypothesis” based on the statistical values of diversity indices. Additionally, it was found that SOM and Pb are the primary factors influencing soil fauna diversity in the remnant forests, while SOM and Zn are the main influencing factors for the dominant soil fauna groups. To elucidate the impact of urbanization on soil fauna biodiversity in remnant forests, future studies should consider other urbanization factors.