Predicting Variability in the Impact of Plant Invasion on C and N Cycling with a Conceptually Driven Framework

EPA Grant Number: F13F31249
Title: Predicting Variability in the Impact of Plant Invasion on C and N Cycling with a Conceptually Driven Framework
Investigators: Lee, Marissa Ruth
Institution: Duke University
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2014 through September 1, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecology

Objective:

Plant invasions can have detrimental consequences for critical ecosystem processes, such as carbon storage and nutrient retention. This project aims to understand factors that drive variability in the effect of one of the most widespread invasive plant species in the eastern United States, Microstegium vimineum, on carbon (C) and nitrogen (N) cycling. Specifically, it will investigate the relative importance of two hypotheses that describe variation in invader impact: first, that species have greater impact where they are most abundant (the mass ratio hypothesis); and second, that species have greater impact where they have the most different ecosystem function than the resident vegetation (the novel-traits hypothesis). In addition, experimental manipulations will determine the relative importance of litter and root-derived invader inputs on soil dynamics in forest plots varying in the dominant nutrient form (inorganic or organic) and, hence, the degree to which resident vegetation function most differently from the invader.

Approach:

Observational studies and field manipulations will be used to study how M. vimineum affects coupled C and N cycling across a landscape that varies in M. vimineum abundance and varies in the degree to which M. vimineum nutrientuse characteristics differ most from the resident vegetation. C and N cycling will be characterized in paired invaded and uninvaded forest plots along a nutrient economy gradient. Plots will be chosen to maximize variation along the nutrient economy gradient based on the tree mycorrhizal status at each plot, because mycorrhizal status is a good indicator of the primary form of nutrients used by plants and microbes in that system. To determine the relative importance of litter and root-derived inputs from M. vimineum on soil C and N cycling across the nutrient economy gradient, a fully factorial experiment will cross root removal with three levels of 15N-labeled M. vimineum litter addition (none, ambient density and double density) in invaded areas at three points along the nutrient economy gradient. Two forest stands with 0–20 percent, 40–60 percent, and 80–100 percent of the trees associated with arbuscular mycorrhizal fungi will be randomly selected for use in this study. M. vimineum’s litter C and N contribution, root C contribution, and total C and N contribution under factorial treatments will be calculated by summing M. vimineum-derived C or N across all soil and microbial pools.

Expected Results:

If the effects of M. vimineum are predicted by the mass ratio hypothesis, the magnitude of M. vimineum’s effect will correlate with its abundance in invaded plots. Alternatively, if the impact of M. vimineum supports the novel-traits hypothesis, the magnitude of M. vimineum’s effect will be greater in forest stands that occupy the organic end of the nutrient economy, where M. vimineum has traits that are dissimilar from the existing dominant nutrient economy. Results are expected to confirm the patterns in M. vimineum’s effect magnitude found across M. vimineum biomass and nutrient economy gradients in the paired plots. It is further hypothesized that M. vimineum litter is more labile than resident litter in systems dominated by organic nutrient forms, thereby promoting litter decomposition; however, M. vimineum is likely to be more nutrient limited in these systems and thus may promote root exudation of labile C to stimulate rhizosphere N mineralization.

Potential to Further Environmental/Human Health Protection

Global climate, soil fertility, ecosystem productivity and ecosystem resilience are all tied to carbon cycling. This project will provide vital information for predicting where and under what conditions invasive species will have the greatest impact on C and N cycling, which will have significant implications for natural areas management and restoration. The focal species is listed by the U.S. Forest Service as one of only 26 Category 1 invasive plants—“highly invasive plants which invade natural habitats and replace native species”—in the Eastern Region of the United States. This research will provide data to generate better predictive models of where M. vimineum is likely to alter ecosystem functions, leading to more efficiently targeted control and restoration efforts and improved strategies for managing and restoring invaded habitats.

Supplemental Keywords:

carbon cycling, nitrogen cycling and deposition, soil fertility

Progress and Final Reports:

  • 2015
  • Final