Effects of Plant Diversity and Functional Identity on Ecosystem Nitrogen Retention and Removal in Great Lakes WetlandsEPA Grant Number: F07F10959
Title: Effects of Plant Diversity and Functional Identity on Ecosystem Nitrogen Retention and Removal in Great Lakes Wetlands
Investigators: Martina, Jason Philip
Institution: Michigan State University
EPA Project Officer: Just, Theodore J.
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text | Recipients Lists
Research Category: Ecological Assessment , Academic Fellowships , Fellowship - Biogeochemistry and Ecosystem Ecology
Human-induced alteration to the global nitrogen cycle has more than doubled the amount of reactive nitrogen entering the biosphere. These inputs have contributed to major ecological and human health problems, such as tropospheric ozone formation, acid rain, increased nitrate levels in drinking water, eutrophication, harmful algal blooms, high biological oxygen demand, and the formation of dead zones. While wetlands provide a host of ecosystem services such as wildlife habitat, flood control, and shoreline stabilization, one of the main services provided by these ecosystems is the enhancement of water quality via the retention and removal of excess N. The central theme of the proposed research program is to investigate the effects of plant community composition on the ability of Great Lakes wetlands to retain and remove nitrogen. The invasion of many Great Lakes wetlands by aggressive invasive species, such as Phalaris arundinacea and Phragmites australis, has resulted in the introduction of novel plant traits that can influence key nitrogen transformation pathways (e.g. nitrification, mineralization, and denitrification). My work aims to determine if the plant traits of the dominant wetland species, such as plant N uptake, biomass production, litter quantity and quality, and rooting depth affects the rate and dominance of the above mentioned nitrogen transformation pathways. It will also be determined if plant diversity affects these ecosystem level processes.
Two study regions will be used in this investigation. One region will be based near the Kellogg Biological Station (KBS) in south-central Michigan and the second region will be the coastal wetlands on the eastern shore of Lake Michigan. At each study region, replicate wetland sites will be identified with native plant community structure as well as sites that have been invaded by aggressive invasive plants, including Phalaris arundinacea and Phragmites australis. At each site, species and functional group diversity will be determined along with species-specific aboveground net primary production (ANPP) and belowground NPP (BNPP). Samples of leaf tissue, litter, and soil will be analyzed for %C and %N. Proximate analysis will be used to quantify concentrations of hot-water soluble carbohydrates, soluble nonpolars, hollocellulose, and acid insoluble material. Compound-specific substrate data will be obtained using 13C-NMR facilities at Michigan State University.
To determine whether plant community structure influences microbial activity by altering organic matter quality, a series of ‘common garden’ soil incubations will be conducted to determine C and N mineralization. Soil microclimates within each site will also be monitored, including soil temperature, water table position, soil redox status, and dissolved oxygen levels. Water samples will be analyzed for pH, electrical conductivity, anion/cation concentrations, and dissolved organic N (DON). N mineralization and net nitrification rates will be quantified in situ using the buried polyethylene bag technique at each site along with laboratory soil incubations. Static chamber techniques and gas chromatography will be used to directly measure N2O flux from five locations in each wetland as a measure of denitrification.
It is predicted that plant N uptake is critical to short-term N retention in wetlands and is influenced by plant community composition and functional group structure. Due to the large biomass production of most invasive species, invaded wetlands should have elevated community level plant N uptake. Plant community composition is expected to control litter and substrate quality, which will influence soil N mineralization and ultimately determine the effectiveness of wetlands in transforming excess N from surface waters. Also, plant community composition should influence N transformations in wetland soils through plant trait controls on soil microenvironments.