Soil salinity initiates a cascade of changes in soil biological communities and activities

Soils in the Northern Great Plains of North America can host high salt concentrations, resulting from geologic origin, and strongly tied to landscape climate and hydrology patterns. Salt concentrations in topsoil can be elevated with intensive management for row crop production. We know that high salt concentrations in topsoil directly impact plant productivity and crop yield; however, our investigations indicate that belowground communities and processes do not necessarily align with patterns of plant productivity. Multiple years of field surveys have revealed that communities and functions of saline soils are distinctly different than non-saline soils. As expected, soils within saline patches tend to have reduced structural development, higher water content, lower surface residues and organic matter incorporation, and elevated soil nutrient concentrations. Thus, the habitat for soil organisms is physically and chemically different than nearby non-saline soils. We have observed that these habitat changes are associated with shifts in soil biological communities (microbial groups, nematodes, arthropods, and earthworms) and their activities (greenhouse gas production and decomposition) in unexpected ways. While total microorganism abundance is fairly stable across the saline and non-saline soils, arthropod, nematode, and earthworm counts are reduced in saline soils. Due to the abundance of microbes, soil water, and labile nutrients in saline soils, we observed elevated greenhouse gas emissions in saline soils. Decomposition rates are stable across salinity levels, providing further evidence that saline soils are microbiologically active despite a paucity of plant production. Given that soil salinity occurs within a suite of soil conditions that influence soil functions, and that these shifts happen over short distances, salinity appears to be an important driver of spatial heterogeneity in soil properties. These observations have implications for intensive, targeted management for mitigating the agroecosystem impacts of salts.