Belowground plant and fungal community response to an accelerated forest succession manipulation
Future climatic conditions are predicted to increase forest disturbances, which could alter productivity, biogeochemical cycles and successional trajectories. Understanding how soil processes, plant and fungal species composition, and nutrient cycles are altered during succession and in response to disturbances is essential for understanding the role forests play in mitigating climate change in a changing environment. The Forest Accelerated Succession ExperimenT (FASET) at the University of Michigan Biological Station presents a unique opportunity to study changes in plant and fungal community structure post disturbance. FASET consists of a 39-ha treatment in which all primary successional Populus tremuloides, P. grandidentata, and Betula paperifera were killed by stem-girdling in 2008. My study asks: How do root and fungal communities differ in a temperate forest following an intermediate disturbance? Given the previously observed increases in maple leaf production and the removal of two ectomycorrhizal associated trees, I predicted that girdling will increase maple root proportions and their arbuscular mycorrhizae. Furthermore, saprotrophs will increase while ectomycorrhizae decline due to fewer ectomycorrhizal host trees and increasing nitrogen availability. In this study I combine molecular and biochemical techniques to test hypothesized mechanisms relating plant and fungal composition to alterations in nutrient cycling post disturbance.
Four years after the girdling treatment overall fungal diversity, plant diversity, and root biomass were similar in girdled and ungirdled stands. Maple roots did not increase as did foliag, which is contrary to our predictions: girdling tended to decrease maple roots (p=0.07). Arbuscular mycorrhizae were similar between girdled and reference treatments. Girdling also decreased ectomycorrhizae (p=0.05) and increased saprotrophs by 7%. Furthermore, ectomycorrhizae proportions decreased with increasing nitrogen availability (p=0.01) while saprotrophs increased (p=0.02) with nitrogen availability. This research illustrates the propensity for disturbances in forest ecosystems to shift nutrient availabilities, and corresponding plant and fungal community compositions. The belowground changes could have implications for carbon storage in soils under future disturbance regimes. More research is needed into the direct mechanism for this decline in ectomycorrhizae, how the shifted community affects fluxes of carbon through the soil, and what the shifts toward a more saprotrophic-dominated system mean for soil carbon storage.