Date of Graduation

12-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Savin, Mary C.

Committee Member

Coffey, Kenneth P.

Second Committee Member

Hays, Phillip D.

Third Committee Member

Norman, Richard J.

Fourth Committee Member

Wolf, Duane C.

Keywords

Biological sciences; Demographics; Earthworms; Endophyte; Nitrogen cycling; Stable isotopes; Tall fescue

Abstract

Evolutionary origin and ecological niche may impact how earthworm species affect N cycling. Tall fescue (Lolium arundinaceum (Schreb) S. J. Darbysh) infection with the toxic endophyte Neotyphodium coenophialum Glenn, Bacon & Hanlin (E+) may influence earthworm communities in soil compared to non-toxic endophyte (NE+) infected tall fescue. Conversely, different earthworms may contribute different amounts of N to E+ vs. NE+ tall fescue. A field survey was conducted from January 2007 to January 2008 to determine the impact of E+ and NE+ tall fescue, planting date, and seasonal variables, e.g. soil temperature and moisture, on earthworm species, abundances, and population age structure. Laboratory studies were conducted using 10-cm dia. cores filled with 20 cm of Captina silt loam and E+ or NE+ tall fescue litter and plants. Cores contained no worms, native, endogeic Diplocardia meansi, non-native, endogeic Aporrectodea trapezoides or anecic Lumbricus terrestris, or a mix of native and non-native earthworms. Litter in E+ cores was labeled with 15N to trace the movement of N from litter into earthworms, soil and live plants. Soil, microbial, dissolved total, organic, and inorganic N concentrations, and microbial activity were measured in E+ and NE+ cores to determine changes in N pools from the activities of different earthworm species. Endophyte type did not result in different adult earthworm populations. Dissolved N pools, but not plant uptake, was higher in the presence compared to the absence of earthworms. Earthworm origin and ecological group did alter N availability under E+ but not NE+ tall fescue. While fescue pastures can be converted to NE+ without altering earthworm communities, introduction of non-native earthworms can alter N cycling. Anecic earthworms increased nitrate to a greater extent than endogeic earthworms under E+, but not NE+ fescue. Further investigation of aboveground-belowground interactions in NE+ and E+ tall fescue systems is warranted.

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