Document: DEB-3-66-7

Comparison of nematode communities in soils exposed to ambient or elevated CO₂ concentrations.

NEHER, D.A.* and T.R.WEICHT

University of Toledo, Toledo, OH 43606, U.S.A. ¹

Abstract:
Elevated CO₂ may increase rates of carbon fixation, resulting in increased labile carbon (root exudates, fine roots) in soil, which provides a food resource for herbivorous nematodes. Numbers and biomass of herbivorous nematodes were compared in soils exposed to ambient or 180 ppm above ambient CO₂ concentrations in a pine plantation at FACE sites near Durham, NC and sweet gum plantation near Oak Ridge, TN. Nematodes were extracted from soil by Cobb's sieving or filtration followed by sucrose flotation, and from litter and roots in a mist chamber. Nematodes were enumerated and identified to taxonomic genus. Biomass was estimated using video image analysis. Data were analyzed using a three-way Kruskal-Wallis test. Elevated CO₂ affected numbers more than biomass of nematodes. There were twice as many nematode genera present in soil (67) than either roots (34) or litter (35). Herbivore genera comprised a larger portion of total genera in roots (26%) and soil (27%) than litter (14%). However, herbivore abundance represented 7, 38, and 15% in roots, soil and litter, respectively; the remainder were free-living nematodes. In the root fraction and subterranean organic matter, elevated CO₂ decreased numbers of herbivores Helicotylenchus and Malenchus. In soil, elevated CO₂ decreased numbers of herbivores Hemicyclophora and increased numbers of Criconemella and Paratylenchus. Furthermore, elevated CO₂ decreased numbers of free-living nematodes Acrobeles, a migratory daure stage, Eudorylaimus, Panagrolaimus and Wilsonema but increased numbers of Acrobeloides, Dorylaimoides and Tripyla. In litter, elevated CO₂ had no effect on numbers of herbivores, increased numbers of bacterivore Rhabditidae and fungivore Nothotylenchus, and decreased numbers of bacterivore Teratocephalus. Given one sampling season, it is yet uncertain whether elevated CO₂ will have a net increase in abundance of herbivorous nematodes or plants have already adapted to nematode feeding which often shifts feeding cells to strong carbon sinks.

Keywords: nematodes, climate change, soil, carbon dioxide

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.