Date Available

10-29-2012

Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Biology

First Advisor

Dr. Mary A. Arthur

Second Advisor

Dr. Philip Crowley

Abstract

Invasive species are significant drivers of global environmental change, altering the stability and functioning of numerous ecosystems. The exotic shrub Lonicera maackii is an aggressive invader throughout much of the eastern United States. While much is known about its population and community impacts, little is known about effects on ecosystem processes.

This dissertation documents changes in ecosystem processes associated with L. maackii growing beneath three native tree species (Fraxinus quadrangulata, Quercus muehlenbergii, Carya ovata) in a savanna in Kentucky. Like many invasive plants, L. maackii litter decomposed and lost nitrogen (N) rapidly, especially in comparison with native tree litter. In comparison to the soils beneath the trees where the exotic shrub was absent, soils beneath L. maackii had a lower bulk density, elevated soil organic matter, C:N, and total soil N and a modified soil microbial community. Inorganic N deposition from spring throughfall was also altered by L. maackii, with higher NO3-N deposition beneath shrubs located beneath the tree canopy relative to canopy locations without L. maackii.

While many exotic plant species have been shown to alter ecosystem processes, their impact is often not uniform. This variability is attributed to among-site differences (soil, climate, plant community): within site variability is often ignored. While many of L. maackii’s alterations to ecosystem processes were uniform across the site, several were dependent upon interactions between the exotic and the native tree species. Litter from L. maackii decomposed and lost N more rapidly under C. ovata than under the other native tree species. Soils beneath L. maackii shrubs located under C. ovata also had a greater fungal:bacterial ratio and a greater abundance of the saprophytic fungal lipid biomarker 18:1ω9c.

These results demonstrate that L. maackii’s impact extends to ecosystem processes and suggests that invasive plants may have variable effects within a given environment depending on their interactions with the dominant native species. Identifying native species or communities that are more vulnerable to alterations of ecosystem function upon invasion may prove useful to land managers and foster a better understanding of the role that community dynamics play in moderating or enhancing invasive species impacts.

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