Grazing altered carbon exchange in a dry mixed-grass prairie as a function of soil texture

Abstract

How soil carbon dioxide (CO2) and methane (CH4) fluxes and above- and belowground C respond to grazing management across a grassland landscape is poorly understood. Thus, we quantified soil CO2 and CH4 fluxes, and above- and belowground C, for sandy loam and loamy sand soils within a dry mixed-grass prairie subjected to annual rotational cattle grazing (grazed) since 1970 or grazing exclusion for 4 yr (rested). Gas samples were collected weekly (May to October). The CO2 flux was 24% greater from the rested than grazed sandy loam. Higher CO2 fluxes from the rested than grazed sandy loam were associated with 49% and 68% greater water-extractable organic C concentrations in May and July, respectively, a 34% greater soil organic C concentration, and 88% greater peak aboveground vegetation C. In contrast, the rested and grazed loamy sand had similar CO2 flux and above- and belowground C, but 16% more CH4 uptake occurred in the grazed than rested. Across soil textures, water-filled pore space (WFPS) explained 59% of early-season CH4 flux variability and 37% overall. Soil respiration and above-and belowground C appeared most responsive to grazing in the soil with finer particle texture, whereas WFPS most strongly controlled early-season CH4 fluxes across soils.