Broad-scale patterns of soil carbon (C) pools and fluxes across semiarid ecosystems are linked to climate and soil texture

Dryland (semiarid and arid) ecosystems are responsible for most of the interannual variation in atmospheric CO2 concentrations and contain a considerable fraction of the globe’s soil carbon (C) stock. Despite their important contribution to the global land C sink, we have a poor mechanistic understanding of the processes that drive C cycling patterns in drylands. In this study in eastern Utah, we examined the natural variation of soil C pools and fluxes along semiorthogonal gradients of climate and soil texture in order to determine the pertinent environmental controls on soil C cycling dynamics. Our study revealed a high degree of collinearity among C stocks and fluxes, which were related to climate, vegetation, and soil clay content. Soil C pools were positively correlated with both soil clay content and precipitation, which in turn was linked to aboveground plant biomass. By contrast, enzyme activities were negatively associated with temperature. We observed a strong decoupling of C pools and fluxes (for example, total C, DOC, microbial biomass C, and respiration) from the enzyme activities involved in organic matter decomposition. Overall, our findings indicate that the within- and between-site variation of soil C pools across diverse dryland ecosystems was strongly linked to both climate and edaphic characteristics, but the high degree of local variability within sites could challenge interpretations of environmental controls at broader scales.