Meghan Hamp, MSc Candidate, Terrestrial Ecosystem Ecology Lab Atmospheric deposition of nitrogen (N) derived from fossil fuel burning is likely to impact the long-term stability of many ecosystems as it can have critical impacts on soil health, plant species diversity, and nutrient cycling. Grassland ecosystems are one of the most important terrestrial carbon sinks that could be utilized to mitigate climate change because of their high productivity, and their significant potential for enhanced soil carbon sequestration due to their rapid turnover of fine roots. Eastern Ontario is currently experiencing atmospheric N deposition levels of ~10 kg N ha-1 yr-1 , and meadow hayfields in the region occur on a wide range of soiltypes. The long-term consequences of enhanced atmospheric N deposition on such grasslands are difficult to predict because their responses to increased low-level N availability may be strongly influenced by factors such as soil texture that have not previously been investigated. A simulated enhanced atmospheric N deposition experiment was set up within a meadow hayfield in Eastern Ontario in 2005 and consists of six replicate treatment and control plots on both clay-based soils and sand-based soils. The objective of this research is to determine the relative impacts of experimentally increased low-level N additions (simulating 2050 atmospheric N input rates) and soil texture on species diversity, above- and belowground biomass and ecosystem carbon dioxide fluxes. The chronic low-level nitrogen additions had no significant impacts on growth of any plant species or on carbon dioxide fluxes. Instead, ecosystem carbon dioxide fluxes were primarily controlled by soil texture, soil temperature, and sampling date over the growing season. Aboveground biomass and species diversity were principally controlled by variation in soil moisture, while belowground biomass did not vary in response to any measured environmental parameters. The consistent lack of responses to the nitrogen addition treatment indicates that future increases in atmospheric nitrogen deposition are unlikely to have major impacts on Ontario’s meadow hayfields. By contrast, the strong interconnected influences of soil texture and soil moisture on multiple community and ecosystem-level properties suggest that effects of anticipated future declines in summer precipitation on subsequent water availability to vegetation will differ among soil-types. Therefore, future climate changes in this region are likely to have very substantial, but highly spatially variable, impacts on plant community structure and carbon cycling in its meadow hayfield ecosystems.
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