Biogeochemical effects of an invasive grass across a land-use gradient: linking alterations of nitrogen cycling to depleted soil carbon pools

An emerging synthesis in invasion ecology is that the effects of invasive plant species depend on spatial context. Therefore, to predict how the functioning of invaded systems will change across spatially heterogeneous landscapes, there is a need to understand the mechanisms underlying the effects of invasive plants and how they may interact with spatially-variable abiotic or biotic factors. I studied the biogeochemical effects of the invasive grass, Microstegium vimineum, to determine 1) whether a common plant-soil feedback involving alterations of nitrogen (N) cycling is linked to declines in soil carbon (C) stocks and 2) whether this mechanism explains variability in the invader’s impacts on soil C across a land-use gradient. To do this, I quantified the effects of M. vimineum on belowground C and N dynamics and enzyme activities in forests across a 45-km urban-rural gradient in Southern Appalachia, USA. Consistent with previous reports, invasion was associated with depleted soil organic C pools and increased N availability. Structural equation modelling demonstrated that N uptake and preference under M. vimineum resulted in greater mass-specific microbial activity which, in turn, led to diminished soil organic C stocks. This suggests that M. vimineum may stimulate the microbial community to mine soil organic matter for N by driving microbial N limitation. As such, I expected that differences in N availability across the urban-rural gradient would lead to differential impacts of M. vimineum on soil C and litter decomposition, with more soil C loss and greater litter decomposition at sites with low N availability. However, I found that this effect was contingent on M. vimineum biomass such that the largest reductions of soil C, but smallest effects on litter decomposition, occurred at plots with low N availability and high invader biomass. Soil C was unaffected or even increased in areas with high N availability and high invader biomass, but these areas had faster litter decomposition rates. Because N availability and M. vimineum biomass tended to be greater in forests within an urban land use matrix, I observed less severe or even opposite effects of invasion on soil C, but greater effects on litter decomposition in these areas. Taken together, my findings demonstrate that N-mediated plant-soil feedbacks may be linked to alterations of other biogeochemical cycles in invaded systems. Furthermore, understanding these linkages enables predictions of how the impacts of invasive plants will interact with other anthropogenic changes.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Craig, Matthew

Contributors dc:contributor

• Fraterrigo, Jennifer M.

• invasive plant
• plant-soil feedback
• carbon cycle
• Nitrogen cycle
• land use
• nitrogen availability

Statement dc:rights

• Copyright 2014 Matthew Craig

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/49773

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/49773