The effects of nitrogen availability on plant species in the boreal tundra ecotone

Abstract

In high latitude biomes, increasing temperatures due to climate change are predicted to increase nutrient availability. Given the boreal region is dominated by plant and fungal species that are adapted to surviving in low nutrient soil, an increase in nutrients like nitrogen may cause a variety of responses in mycorrhizae fungi and their host plants. I found that several plant species responded to three years of 10 – 100 kg ha-1 nitrogen addition by changing their leaf N isotope ratios, morphology and physiology. However, these changes showed no obvious correspondence with mycorrhizal status. Although ectomycorrhizal fungi slow down the mineralization rates of nitrogen, and help to immobilize nitrogen, both ectomycorrhizal host plants, Picea glauca (Moench) Voss, and Dryas integrifolia Vahl, increased in total chlorophyll ∂15N while lowering the C:N ratio within their tissue due to fertilizer. The ericoid host plants (Ledum decumbens (Aiton) Lodd. ex. Steud, Vaccinium uliginosum L., and Empetrum nigrum L.) all responded differently from one another and did not respond to nitrogen unlike the ectomycorrhizal host plants. These results suggest that mycorrhizal types do not predict how boreal plant species will take up and utilize inorganic nitrogen. In some regions, climate change has resulted in boreal forests range expanding northwards, especially with a northward shift of coniferous trees. Northward range expansion for conifers on the tundra may involve the establishment and expansion of tree islands: clusters of conifers that create microhabitats on their leeward side. While we predicted these microhabitats would benefit conifer establishment and survival, we did not find this. After planting P. glauca and Pinus banksiana Lamb, seed around tree islands near Churchill, Manitoba, I found higher germination further away from the tree islands and on the windward side.