Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

Tharayil, Nishanth

Committee Member

Kerrigan , Julia

Committee Member

Wells , Christina

Abstract

Plant species invasion is problematic around the world due to its negative effects on native plant biodiversity, ecosystem function, and ecosystem stability. Understanding the mechanisms of plant species invasion is necessary to predict new invasions and to control current problematic species. Polygonum cuspidatum Sieb. & Zucc. (Polygonaceae, Japanese Knotweed) is an invasive species found in 40 of the 50 United States and listed as a noxious species in nine states. It is known to exclude native plant communities, and its eradication is nearly impossible. The extensive negative effects associated with this species make understanding its mechanism of invasion a prerogative. To this end, I have examined belowground mutualisms and shifts in nutrient cycling associated with P. cuspidatum in the United States.
Mycorrhizal symbioses are present in the vast majority of vascular plants. However, the benefits of invasive plant species association with native belowground communities, in terms of biomass accumulation, are not well known. I paired an invasive plant species, P. cuspidatum, with the native belowground community from an invaded site in the upper piedmont of South Carolina. Through limitation of phosphorous and arbuscular mycorrhizal (AM) inoculum in a greenhouse experiment, I sought to determine the benefits of association between the plant and AM fungi, in terms of increased biomass accumulation. I found that P. cuspidatum associated with the native AM community and also formed associations with dark septate endophytes (DSE), a lesser known and potentially mycorrhizal group.
Next, I determined nitrogen levels in soils collected inside and outside of the zone of invasion of P. cuspidatum across the eastern United States. Previous studies have examined the nitrogen pool as a whole, potentially confounding the effects of the study species on plant-available and plant-unavailable nitrogen pools. I fractionated the nitrogen pool into nitrate, which is plant available, and total nitrogen less nitrate (TNLN), which is composed of organic forms of nitrogen and ammonia. I found that, while not all sites differed, nitrate levels increased with the presence of P. cuspidatum.

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