Soil Bulk Density and Matric Potential Regulate Soil CO 2 Emissions by Altering Pore Characteristics and Water Content

Soil pore structure and soil water content are critical regulators of microbial activity and associated carbon dioxide (CO 2 ) emissions. This study evaluated the impacts of soil bulk density and matric potential on carbon dioxide (CO 2 ) 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 CO 2 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 CO 2 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 CO 2 emissions. Proper management of soil structure and water content is therefore essential to support soil ecological functions and associated ecosystem services.