Effects of long-term nitrogen and sulfur deposition on soil microbial communities and soil properties in the Athabasca oil sands region in northern Alberta, Canada

Abstract

Intensified oil sands activities have resulted in elevated levels of nitrogen (N) and sulfur (S) deposition in the mixedwood boreal forest in the Athabasca oil sands region (AOSR) of northern Alberta, Canada. The deposition of N and S can affect the surrounding ecosystem and it is important to monitor possible effects. To improve the understanding of the response of boreal forest ecosystems to increased N and S deposition in the AOSR, an experiment was established in 2006 with the following treatments: control, +N addition (30 kg N ha-1 yr-1 as NH4NO3), +S addition (30 kg S ha-1 yr-1 as Na2SO4), and +NS addition (30 kg N plus 30 kg S ha-1 yr-1). Nine years of simulated N and S deposition did not affect soil bacterial diversity, community composition, abundance, functional profiles, and co-occurrence patterns, suggesting that soil bacteria were resistant or resilient to increases in N and S addition in the studied boreal forest. In contrast, increased N and S addition increased the abundance of soil fungal communities, suggesting fungi were more sensitive than soil bacteria. Additionally, ten years of simulated N and S deposition did not change soil chemical properties including soil pH, cation and N concentrations and leaching of N below the main rooting zone. Therefore, there was no evidence of N saturation or soil acidification in the experimental forest ecosystem in the AOSR after ten years of N and S addition. Continued long term research of N and S deposition in the AOSR is needed to enhance the current level of understanding and to quantify the collective ecosystem impacts.