Plant roots are often associated with mycorrhizal fungi. i.e. mushrooms that colonize plant roots belowground, and play a crucial role in plant uptake of nitrogen (N) which is essential for plant growth. During this fieldwork we will take soil cores at the peak of the growing season to examine the vertical distribution and biomass of roots along the soil profile. Mycorrhizal colonization of plant roots will be determined, and frost damage on the rain-on-snow (ROS) plots will be recorded. With the N15 labelling method we will determine the amount of N that plants take up from the thawed permafrost. This is done by injecting trace amounts on N15, which is isotopically labelled ammonium, to the permafrost thaw front and after two weeks collecting plant leaves and analyzing the N15 content in them.
We predict that fast growing grasses with a deeper rooting system should have greater access to permafrost nitrogen (N), when the permafrost is thawing, compared to dwarf shrubs. However, dwarf shrubs which are often associated with mycorrhizal fungi with strong enzymatic activities will have a competitive advantage to acquire permafrost N. We expect goose grubbing and ROS to reduce plant access to permafrost N by reducing mycorrhizal mycelium (i.e. the fungal network found belowground); grubbing will cause physical soil disturbance and root damage, and ROS will damage plants through severe frost damage during the winter. These are both increasing in the Arctic due to climatic factors, the migratory geese in number and the ROS events in frequency, and both can affect permafrost thaw over large geographical scales.