Vegetation and Moisture Controls on Soil C Mineralization in Semi-Arid Environments

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Soil Science Society of America Journal



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Mechanisms of vegetation control on C mineralization in semiarid ecosystems are not well understood. We developed a series of model predictions for beneath the native shrub Wyoming big sagebrush [Artemisia tridentata (Nutt.) ssp. wyomingensis], the invasive annual grass cheatgrass (Bromus tectorum L.), and the exotic introduced perennial grass crested wheatgrass [Agropyron desertorum (L.) Gaertn.]. Soil samples (0–10 cm) collected biweekly for two growing seasons were analyzed in the laboratory for: water content, CO2 from intact soil cores and CO2 from soils sieved and wetted to 23%, total organic C, total N, and microbial biomass C. Our results suggest that different vegetation types in the Great Basin affect C mineralization primarily through modification of soil moisture and, secondarily, the amount of labile C. Soils beneath cheatgrass and sagebrush canopy retained more water after high‐and moderate‐intensity rainfalls than soils beneath crested wheatgrass and sagebrush interspace. Sagebrush canopy probably intercepts more incoming precipitation without significant throughfall to the soil surface below than cheatgrass or crested wheatgrass. At the same time, soils beneath cheatgrass had 8% more labile C and 36% higher C mineralization rates than sagebrush. Regression analysis showed that soil water content alone explained nearly 84% of the variation, and adding information on labile C accounted for nearly 88% of the variation in soil C mineralization rates. With increasing variability of precipitation in this region, the continuously increasing presence of cheatgrass in the semiarid and arid western United States may significantly impact the CO2 contributions to overall greenhouse gas emissions.

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