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Title: A Comparison of Soil Food Webs Beneath C3- and C4-Dominated Grasslands

Author
item DORNBUSH, MATHEW - IA STATE UNIVERSITY
item Cambardella, Cynthia
item INGHAM, ELAINE - SOIL FOODWEB, INC
item RAICH, JAMES - IA STATE UNIVERSITY

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2008
Publication Date: 10/16/2008
Citation: Dornbush, M.E., Cambardella, C.A., Ingham, E.R., Raich, J.W. 2008. A Comparison of Soil Food Webs Beneath C3- and C4-Dominated Grasslands. Biology and Fertility of Soils. 45:73-81.

Interpretive Summary: Soil microorganisms break down plant material and convert the chemically-bound nutrients into forms that are available for plant uptake and growth. This process is influenced by many factors, including the type of plant material being decomposed and the kinds and numbers of organisms in the soil. If nutrients are released into the soil when plants don't need them, they can be lost and soil fertility can be reduced. We found no difference in the kinds or numbers of microorganisms isolated from soil taken from several types of perennial grass plots. However, we did find differences in the kinds and/or numbers of soil microorganisms isolated from soil at various times throughout the year. The results tell us that plant material type didn't control the kinds and numbers of soil microorganisms in these experiments. The information will be useful to scientists interested in soil microbial communities and their impact on soil nutrient cycling processes.

Technical Abstract: Soil food web structure influences soil organic matter mineralization and plant nutrient availability, but the potential for plants to capitalize on this mechanism by altering soil food web structure has received little attention. We evaluated this potential mechanism by measuring soil food web structure from May 2001 to October 2002 beneath C3 and C4 dominated grass filter strips in central Iowa, U.S.A. Trophic groups investigated included active and total bacterial and fungal biomass; amoeba, flagellate, and ciliate abundances; and populations of bacterial-feeding, fungal-feeding, root-feeding, fungal-root feeding, and predatory nematodes. Nematode guild taxa diversity was also measured over the same period. First, we tested the hypothesis that lower C3 litter C:N should promote bacterial-based energy channels (i.e. bacteria, protozoa, and bacterial-feeding nematodes), while greater C4 production of higher C:N tissues should increase fungal biomass and top predatory nematode abundance. We also hypothesized that the lower root C:N of C3 grasses would increase root-feeding nematode abundance. Second, with distinct differences in aboveground plant growth phenologies, we hypothesized that C3 and C4 grass effects would be greatest in spring and summer, respectively. In contrast to our hypotheses, we found minimal differences in soil food web structure. Only soil ciliate abundance and bacterial biomass measures differed significantly between vegetation types, and in direct contrast to our initial hypothesis both were greater under C4, not C3, grasses. We also found no significant difference in root-feeding nematode abundance or nematode taxon diversity. Soil food web structure varied significantly among sample dates, but this effect was independent of general seasonal patterns and aboveground plant growth phenologies. Our results add to growing evidence that plant identity plays a minor role in structuring soil food webs in high-carbon soils.