Mccormick, Melissa , Morcol, Taylan , Saunders, Jaclyn , Szlavecz, Katalin , Whigham, Dennis .
Direct and indirect effects of non-native earthworms on mycorrhizal fungi.
Non-native earthworms have been introduced into many ecosystems throughout North America, including forests lacking and with native earthworm communities. In forests devoid of native earthworms, non-native earthworms have been found to decrease arbuscular mycorrhizal colonization of tree seedlings. This decreased colonization could be an indirect effect of earthworms increasing nutrient availability and so decreasing plant need for mycorrhizal fungi or a direct negative effect of earthworms on fungi that might form mycorrhizae. Non-native earthworms change soil microbial communities from fungal-dominated to bacterial dominated. Decreases in the abundance of soil fungi can negatively affect tree species that interact with mycorrhizal fungi to obtain nutrients that they need for growth. We are conducting laboratory and field manipulations to determine whether earthworms affect different types of mycorrhizal fungi (arbuscular and ectomycorrhizal) equally, and whether those effects are direct or indirect.
We used physical manipulations to mimic the different ways earthworms influence soil structure. We examined the effects of mixing soil horizons and disrupting fungal hyphae, crossed with the effects of earthworm cast addition, in field mesocosms. We used quantitative real-time PCR to quantify bacteria, fungi, arbuscular mycorrhizal fungi, and the two dominant ectomycorrhizal genera (Tomentella and Russula) and related these to activity of polyphenol oxidase (PPO), n-acetyl glucosaminidase (NAG), and B-glucosidase (BG) enzymes. We found that both mixing and fertilization decreased the abundance of both ectomycorrhizal fungi. Addition of earthworm casts increased BG and decreased PPO activity, while mixing had the opposite effect, suggesting that mixing increased accessibility of soil carbon pools. Effects of hyphal disruption were variable. We use these results to interpret differences in mycorrhizal colonization and tree seedling growth among field study plots with and without abundant earthworms.
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1 - Smithsonian Environmental Research Center, P.O. Box 28, 647 Contees Wharf Rd., Edgewater, MD, 21037, USA
2 - Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, MD, 21037, USA
3 - Johns Hopkins University, Dept. of Earth and Planetary Sciences, Baltimore, MD, 21218, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Cottonwood C/Snowbird Center
Date: Wednesday, July 29th, 2009
Time: 1:45 PM