Effect of plant species diversity and composition on soil organism

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Effect of plant species diversity and composition on soil organism functional diversity in
an establishing pasture.
Michel McElroy1, Yousef a. Papadopoulos2, and Sina Adl1.
1
Dalhousie University, Dept. Biology, 1355 Oxford St., Halifax, NS B3H 4J1 Canada;
Agriculture & Agrifood Canada, Nova Scotia Agricultural College, PO Box 550, 100-5
Haley Institute, 58 River Road, Truro, NS, Canada B2N 5E3
2
The relationships among ecosystem diversity, productivity, and stability are central to
current ecological research, and links between above-ground and below-ground
ecosystems are becoming more apparent. These links are of particular importance in
agro-ecosystems, where the soil organism community can have significant effects on
plant productivity and health. The main objective of this study was to determine the
relationship between plant species diversity and the functional diversity of soil microorganisms. Thirty-six plots were established in an experimental pasture seeded with a
combination of timothy (Phleum pratense), white clover (Trifolium repens), Canada
bluegrass (Poa compressa), reed canarygrass (Phalaris arundinacea), and meadow
fescue (Festuca pratensis). Each plant combination was then grouped into a diversity
treatment based on the number of plants seeded in the plot (1 to 5). Soil samples were
taken three times over the growing season (early summer, late summer, and fall)
immediately prior to grazing in 2005 and 2007. Bacterial activity and functional
diversity, Nematodes and microarthropods (mites and collembolans) were extracted from
fresh soil samples and assessed. Plant biomass and plant species composition were also
determined. Functional diversity of all biological groups was assessed using the ShannonWiener index, while differences in diversity and abundance of soil groups over
composition and diversity treatments were assessed using analysis of variance and
Tukey's post-hoc test. Multivariate methods were used to further investigate plant-soil
links. While plant diversity and composition did affect sward productivity, the
abundance and functional diversity of soil organisms were generally not significantly
different across treatments. Discriminant analysis of bacteria catabolic activity
demonstrated that bacterial substrate use differed markedly across plant composition
treatments, while the largest changes in soil fauna occurred over sampling dates. We
conclude that the functional diversity and overall abundance of soil organisms may not be
responsive to changes in plant species diversity nor composition in the short term, but
that soil community composition may be affected.
Keywords: plant community, biodiversity, soil biology, functional diversity, pastures.
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