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

Mary C. Savin

Committee Member

Kenneth P. Coffey

Second Committee Member

Phillip D. Hays

Third Committee Member

Richard J. Norman

Fourth Committee Member

Duane C. Wolf

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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