Mycorrhizas under Arctic shrub expansion: Effects of temperature, nutrient limitation, and host species on symbiotic root processes

• Main Author: Dunleavy, Haley Rose
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: QK Botany; Arctic; Tundra; Alaska
• Online Access: https://openknowledge.nau.edu/id/eprint/5752/; https://openknowledge.nau.edu/id/eprint/5752/1/Dunleavy_2021_mycorrhizas_under_arctic_shrub_expansion_effects_tempera.pdf

In the nutrient limited Arctic tundra, mycorrhizae greatly influence nutrient cycling, providing up to 86% of nitrogen (N) to their host plants. As the Arctic warms, both nutrient availability and mycorrhizal host shrub abundance are increasing in tundra ecosystems. The resulting changes in mycorrhizal community and function are likely to affect not only nutrient, but also carbon (C) dynamics. In this dissertation, I studied how mycorrhizal-associated nutrient cycling may change with future warming, increased nutrient availability, and shifts in host plant abundance by pairing measurements of degradative extracellular enzymes on mycorrhizal roots with 1) mycorrhizal fungal identity, 2) aboveground plant abundance and height, and 3) another symbiotic root process occurring on the same shrub—N fixation. In chapter 2, I tested the effects of long-term experimental warming and fertilization on ectomycorrhizal fungal community and root enzyme activity. Warming tended to increase enzyme activity while fertilization decreased activity. Though these responses were partially explained by changes in EcM fungal community, our findings also suggest changes in enzyme activity were taxon-specific. In chapter 3, I further tested how nutrient limitation affected EcM as well as ericaceous shrub abundance and root enzyme activity, measuring non-linear responses across a long-term experimental soil fertility gradient. I found evidence of the co-expansion of ericaceous shrubs along with deciduous EcM shrubs and support for the potentially increased relative importance of EcM root enzymes compared to those of ericaceous roots in the degradation soil organic matter a future tundra. In chapter 4, I explored drivers of root enzyme activity and N fixation on Siberian alder, a deciduous EcM shrub found in boreal and Arctic Alaska. Across a latitudinal gradient, root enzyme activity and N fixation were correlated. Furthermore, the direction of this correlation appears to depend on relative availability of soil N and phosphorus. Overall, ...