Semester

Spring

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Jonathan Cumming

Committee Member

Stephen DiFazio

Committee Member

William Peterjohn

Committee Member

Louis McDonald

Committee Member

Jingjing Liang

Abstract

Since the colonization of North America by Europeans, ecosystems in Appalachia and across the continent have been in a prolonged state of flux. Areas particularly rich in natural resources, such as Appalachia, have historically borne the brunt of these swift changes, often with devastating consequences. Downwind of much of the power generation facilities of the Ohio Valley, Appalachian forests have been geographically predisposed to high rates of acidic deposition, a circumstance mitigated by the passage of Clean Air Legislation beginning in the 1970s. Nevertheless, decades of elevated nitrogen (N) and sulfur (S) inputs had a profound impact on the ecology and biogeochemistry of these forests. While inputs of these important plant nutrients can provide fertilization effects on plant life, the acidic N and S forms deposited in precipitation also result in a variety of negative outcomes. Plant nutrition can be influenced by acidic inputs in a variety of ways, including modifications to decomposition processes. Microbially-mediated decomposition results in the liberation of nutrients from organically-bound, often recalcitrant forms. When nutrients are abundant due to acidic deposition or by tree species effects such as N fixation and/or readily decomposable low C/N litter, decomposition processes may be suppressed. Since extracellular soil enzymes (ESEs)–the biomolecules responsible for mediating many of the rate-limiting transformations in terrestrial nutrient cycling–are metabolically expensive, and their synthesis and activities tend to be suppressed under nutrient fertilization. In Chapter 2, I present a literature review of ESE activities in the context of their ecosystem function and responses to disturbance, such as different types of pollution episodes, including acidic deposition. In addition to alterations to forest soil decomposition processes, acidic deposition may have other consequences on forest biogeochemistry. Poorly-buffered forest soils are particularly vulnerable to losses of essential nutrient cations, overriding any potential benefits from plant fertilization effects. In addition, the liberation of phytotoxic aluminum cations in an acidifying soil substrate can be extremely detrimental to plant growth. I hypothesize in Chapter 3 that I will observe declines in soil and foliar nutrient element concentrations as modeled estimates of cumulative historic N deposition in high-elevation red spruce forests increase. Likewise, Chapter 4 considers the effects of acidic deposition in the same ecosystem, testing the hypothesis that ESE activities will decline in concert with a legacy fertilization effect still present in high elevation red spruce forest soils. Lastly, I examine the relationships between plant functional guilds and soil processes using the Stand Initiation and Diversity Experiment (SIDE) at Point Pleasant, West Virginia. I hypothesize that I will observe differences in ESEs in plots dominated by different functional guilds of woody tree species: those bearing arbuscular mycorrhizal symbioses, ectomycorrhizal symbioses, and those capable of fixing N. This research will investigate the interplay between anthropogenic disturbances to ecosystem processes, legacy effects due to historic disturbances, tree species effects on ecosystem processes, and the role of tree species functional guilds on ESE profile and decomposition. Observing the effects of past disturbances will provide insight on the nature of contemporary and future changes to natural systems.

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