Soil Bulk Density and Matric Potential Regulate Soil CO2 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 (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.