Research on biocrusts in degraded subtropical karst ecosystems remains limited, and the few reports that are available focus on only one small area. Here, we assessed the effects of moss crusts on soil physicochemical properties, enzyme activities, and bacterial communities in four subtropical karst ecosystems experiencing varying degrees of degradation. We also explored the response mechanisms underlying moss crusts' ecological functions along the same eco-degradation gradient. Our results indicate that moss crusts influence soil enzyme activities and physicochemical properties in the same way in each of the four karst ecosystems, regardless of the degree of degradation: moss crusts significantly improved soil physicochemical properties and enhanced aggregate stability (soil organic carbon, total nitrogen, alkali-hydrolyzable nitrogen, available kalium, silt + clay content, and soil aggregate mean weight diameter) and enzyme activities (N-acetyl-beta-D-glucosidase, leucine aminopeptidase, beta-glucosidase, and sucrase). Moss crusts greatly enhanced soil bacterial community species richness, except in HF with a much lower pH (5.35 similar to 6.08), suggesting that the connection between moss crusts and bacterial species richness is most relevant in weakly alkaline (HJ and KD) and nearly neutral (YT) karst environments. Soil enzyme activities and chemical properties are more dominant drivers influencing bacterial communities within moss crusts in karst ecosystems with different degrees of degradation. Furthermore, moss crusts significantly enhanced the stability and complexity of soil bacterial networks in all study areas except HF. The influence of moss crusts on soil properties (total nitrogen, mean weight diameter, and sucrase) and bacterial network structure became stronger with an increasing degree of degradation, and interactions between soil bacterial taxa tended to become increasingly cooperative. This study deepens our understanding of the ecological functions of moss crusts in different ecosystems and offers a theoretical reference for the study of how biocrusts and their ecological functions respond to global climate change.