The Role of Plant Functional Diversity and Soil Amendments in Regulating Plant Biomass and Soil Biogeochemistry in Restored Wetland Ecosystems in the North Carolina Piedmont
Abstract
Human actions have led to the destruction or degradation of natural habitats in virtually
all parts of the Earth. Ecosystem restoration is one method to mitigate the effects
of habitat loss. But restoration ecology is a young discipline and there is much
left to be learned about how to effectively restore ecosystem functioning. This dissertation
examines how soil amendments and planted herbaceous species diversity affect the restoration
of ecosystem functions in wetlands, while also testing basic ecological questions
that help us understand ecosystem function. Using data from the greenhouse and from
the biodiversity and ecosystem function field experiment in Duke Forest, in Durham,
NC, I examine how plant trait diversity, average plant traits, and environmental conditions
influence nitrogen (N) removal from restored wetlands. Field data collected from
a restored wetland in Charlotte, NC, enables me to examine how soil organic amendments
influence the development of soil properties, processes, and plant communities. Finally,
combining field data from both sites, I compare how soil properties influence denitrification
potential in both restored wetlands.
One unanswered question in the research relating biodiversity and ecosystem function
is whether species diversity or species traits are more important drivers of ecosystem
function. The first portion of my dissertation poses several hypotheses about how
plant traits, plant trait diversity (calculated as a multivariate measure of plant
trait diversity), and environmental conditions are likely to influence two ecosystem
functions, biomass N and denitrification potential (DEA), and then examines these
hypotheses in a restored wetland in the Piedmont of N.C. Using multiple linear regression,
I demonstrate that functional diversity (FD), of traits important for plant growth
had no effect on biomass N, but two plant traits, leaf area distribution ratio (LADR)
and water use efficiency (WUE), had strong negative effects. Soil inorganic N also
had a positive effect. For DEA, FD of traits related to denitrification also did
not have a significant effect, but there was evidence of a weak positive effect.
Two plant traits had positive effects on DEA, aboveground biomass and aboveground
biomass C:N ratio; two traits, belowground biomass C:N ratio and root porosity, had
negative effects. Soil inorganic N and soil organic matter also had positive effects
on DEA. Results from a Principal Components Analysis (PCA) clustering plant species
in trait-space, suggest that Carex, Scirpus, and Juncus species tend to be associated with traits that maximize biomass N, while there is
no specific region of trait space or set of species that correspond to high DEA.
Instead, there are multiple plant trait combinations that can lead to high DEA. These
results suggest that, even though plant diversity (as measured by FD) does not significantly
influence biomass N or denitrification, plant trait diversity is important to maintaining
multiple ecosystem functions simultaneously.
Restored wetlands tend to have lower levels of soil organic matter than natural reference
wetlands. Low soil organic matter can limit nutrient cycling as well as plant survival
and growth in restored wetlands. In the second portion of my dissertation, I examine
how soil compost amendments influence the development of soil properties and processes
as well as plant communities at a restored wetland in Charlotte, NC. Using two-way
analyses of variance, multiple comparisons of means, and regression, I determine that
available N and phosphorus (P) increase with increasing soil organic matter in both
the low and high marsh. Total microbial biomass (MB) and microbial activity (measured
by denitrification potential (DEA)) also significantly increase with increasing organic
matter in both marsh communities, as does soil moisture. Neither total plant biomass
(in the low marsh), nor plant species richness (in the high or low marsh) demonstrate
any consistent patterns with soil organic matter level in the first three years post-restoration.
These results suggest that compost amendments can positively influence some soil properties
(i.e. soil available N, P, microbial biomass, and soil moisture) and some ecosystem
functions including nutrient cycling (such as denitrification potential), but may
have limited early impacts on plant communities.
In restoration ecology there is a general assumption that restoring ecosystem structure
will also restore ecosystem function. To test this fundamental assumption, I examine
whether two restored wetlands demonstrate similar general relationships between soils
variables (i.e. do the two systems have similar soil ecosystem structure), and whether
the importance of each soil relationship is the same at both systems (i.e. do the
two systems demonstrate the same soil function). I use structural equation modeling
to both pose hypotheses about how systems function and to test them using field data.
I determine that the same model structure of soil relationships is supported by data
from these two distinct, yet typical urban restored wetland ecosystems (that is, the
two systems have similar soil structure). At both systems higher soil organic matter
is the most important predictor of higher DEA; however, most of the other relationships
between soils variables are different at each system (that is, the two systems are
not functioning in the same way). These results suggest that some fundamental relationships
between soil properties and microbial functioning persist even when restored wetlands
have very different land-use histories, plant communities, and soil conditions. However,
restoring similar soil ecosystem structure does not necessarily lead to the restoration
of similar soil function. Ultimately, I hope this research advances our understanding
of how ecosystems function and improves future wetland restoration efforts.
Type
DissertationDepartment
EcologySubject
Biology, Ecologywetland restoration
wetland biogeochemistry
biodiversity and ecosystem function
functional diversity
denitrification potential (DEA)
soils
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https://hdl.handle.net/10161/620Citation
Sutton-Grier, Ariana E. (2008). The Role of Plant Functional Diversity and Soil Amendments in Regulating Plant Biomass
and Soil Biogeochemistry in Restored Wetland Ecosystems in the North Carolina Piedmont.
Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/620.Collections
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