Impacts of Deicing Salt and Nitrogen Addition on Soil Nitrogen and Carbon Cycling in a Roadside Ecosystem

Roads and highways play an important function in the human-dominated Earth landscape and strongly affect the environment. Roadside ecosystems receive a number of pollutants, including deicing salt and inorganic nitrogen (N) from automobiles. We investigated how soil carbon (C) and N cycling were impacted by the application of salt (NaCl) and nitrate (NO₃⁻) to experimental plots in a field that is adjacent to Interstate 81, in Binghamton, NY. Experimental plots were constructed on two parallel transects; one was adjacent to the highway (0-m) and the other 50 m away from the highway (50-m). We hypothesized that the 0-m transect was exposed to roadway-derived pollutants over a long-term period of time, while the 50-m transect was exposed to fewer pollutants due to its distance from the road. Soils were collected in July and November 2011 and June and October 2012. Salt significantly decreased the rates of soil C mineralization and in situ soil respiration in both 0- and 50-m transects (p < 0.001), though it did not discernibly affect the rates of N mineralization or nitrification. Applications of NO₃⁻ had no significant impact on soil C or N mineralization. The effects of roadway pollutants were reflected in higher soil conductivities and pH at the 0-m transect. Under experimental salt treatment, C mineralization was reduced by 75% in the 50-m transect, compared to 20% reduction in the 0-m transect. We conclude that microbial communities near roads might have evolved to better withstand the impacts of roadway pollutants. Nevertheless, roads and vehicle traffic have strong impacts on the environment, and the application of road salt has important environmental consequences.