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Fungal Community Structural and Functional Responses to Disturbances in a North Temperate Forest

TitleFungal Community Structural and Functional Responses to Disturbances in a North Temperate Forest
Publication TypeThesis
Year of Publication2021
AuthorsCastillo BT
Academic DepartmentEcology and Evolutionary Biology (EEB)
UniversityUniversity of Michigan
CityAnn Arbor
Thesis TypeDissertation

Globally soils contain three times as much carbon (C) as the Earth’s atmosphere, with an
additional 5-10% as much C stored in coarse woody debris as in the atmosphere. Due to the large
sizes of these organic C stocks, small shifts in the amounts of soil organic matter, coarse woody
debris, and the microbial communities responsible for decomposition could have large effects on
global carbon cycle. In this dissertation I combine a series of observational and manipulative
experiments to analyze fungal community responses to historical and predicted future
disturbances in a forest ecosystem. I explore how fungal communities respond spatially and
temporally to clear-cutting and burning, and whether they follow trends in diversity predicted by
the intermediate disturbance hypothesis (IDH). In Chapter II, I investigate the short-term effects
of clear-cutting and prescribed burning on fungal community composition and function in
mineral soils, and how spatial variation in disturbance severity within a 1-ha plot structured these
communities. I observed differential effects of clear-cutting or clear-cutting + burning within a 1-
ha stand and found that the areas of highest burn disturbance yielded lowest fungal diversity and
extracellular enzyme activity (EEA). High burn areas also tended to drive plot level differences
in soil physio-chemical properties with increases pH and effective cation exchange capacity
(ECEC), while plot level increases in fungal diversity were driven by areas that primarily
received the clear-cutting disturbance. My results highlight the importance of spatial variation
and scale of sampling when examining both abiotic and biotic responses to disturbances. In
Chapter III, I leveraged an existing +100-year cut+burn chronosequence to explore whether soil
fungal communities follow decadal patterns in successional trajectories predicted and often
observed in plant communities by the IDH. I found that plant community diversity in the
chronosequence adhered to patterns predicted by the IDH, however, fungal diversity did not
follow similar trajectories. Fungal diversity was lowest in the 61-year old mid-successional plot.
The low diversity observed in this plot was primarily attributed competitive exclusion due to a
dominance of ectomycorrhizal taxa in the Cortinariaceae that was accompanied by a high
abundance of oaks relative to the other experimental plots. When the successional patters were
analyzed with just the remaining chronosequence plots diversity was seen to decrease with
successional stage. Conversely, I observed a steady increase in microbial abundance into later
successional stages reflecting similar patters observed in primary producer productivity. In
Chapter IV, I investigated patters of fungal decomposer communities in coarse woody debris of a
pioneering tree species in temperate forests, Populus grandidentata, from standing dead trees to
the incorporation of woody necromass into soil. I showed that fungal communities are dynamic
during and after a decay class continuum, colonizing while trees are standing and continuing to
shift throughout coarse woody debris decay. Specifically, I note that nitrogen is an important
driver of enzymatic activity in microbial communities and show a correlation with bacterial and
fungal species composition and abundance along the continuum of decay. Overall, the work
described here offers further support for the importance of disturbances in structuring soil fungal
communities. Notably, my work highlights the importance of spatial variability in disturbance
severity and long-term legacies on fungal composition, activity, and successional trajectories.

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