Soil pore structure and soil water content are critical regulators of microbial activity and associated carbon dioxide (CO₂) emissions. This study evaluated the impacts of soil bulk density and matric potential on carbon dioxide (CO₂) emissions through modifications of total porosity, air-filled porosity, water retention, and gas diffusivity. Soil samples were manipulated into four bulk densities (1.0, 1.1, 1.2, and 1.3 Mg m⁻³) and ten matric potential levels (−1, −2, −3, −4, −5, −6, −7, −8, −9, and −10 kPa) in controlled soil cores. The results showed that lower bulk densities enhanced while higher densities suppressed CO₂ emissions. Similarly, wetter matric potentials decreased fluxes, but emission increased with drying. Correlation and regression analyses revealed that total porosity (r = 0.28), and gravimetric water content (r = 0.29) were strongly positively related to CO₂ emissions. In contrast, soil bulk density (r= −0.22) and matric potential (r= −0.30) were negatively correlated with emissions. The results highlight that compaction and excessive water content restrict microbial respiration and gas diffusion, reducing CO₂ emissions. Proper management of soil structure and water content is therefore essential to support soil ecological functions and associated ecosystem services.

The deteriorating soil health under continuous monoculture is commonly found across various cropping systems. This study evaluated the effects of different tillage practices (conventional tillage and no till) and species mixtures (legumes and grasses) on arbuscular mycorrhizal fungi (AMF) community properties, soil nutrients, and enzyme activity in a 3-year experiment. Compared with traditional tillage, the number of AMF species under no-till conditions was increased, with the Glomus group being dominant. Under different tillage conditions, TN (total N) and AN (available N) contents under no till were significantly higher than those under conventional tillage, while no significant differences among other nutrients were found. The activities of soil acid phosphatase (S-ACP), soil dehydrogenase (S-DHA), and soil sucrose (S-SC) under conventional tillage were significantly higher than those under no till, and the cover crop mixtures also had an exclusive advantage in yield. Soil organic matter (SOM) indicated a significant negative correlation with glomalin-related soil protein (GRSP). The increase in diversity associated with the AMF species community was strongly correlated with the increase in three enzyme activities, and AN was negatively correlated with all species. Tillage did not significantly change soil chemistry, except for AN, and the high concentration of AN led to a decrease in AMF species. The results of this study showed that no till was an effective measure for enriching soil micro-organism population. Additionally, soil AMF diversity was improved by cover crop mixtures, and microbial diversity was higher than that under monoculture cover crops. Different AMF groups responded differently to tillage and cover crop mixtures. Across all mixtures, the combination of hairy vetch (Vicia villosa R.) and ryegrass (Lolium perenne L.) performed the best.