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Soil mite biodiversity: its relationship to grass species and influence on decomposition in the Konza tallgrass prairie

Date

2005

Authors

St. John, Mark George. author
Wall, Diana H., advisor
Hunt, H. William, committee member
Kondratieff, Boris C., committee member
Seastedt, Timothy R., committee member
Stohlgren, Thomas J., committee member

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Journal ISSN

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Abstract

Human activities are responsible for unprecedented extinction rates and global change. Species are disappearing faster than we can record their existence and before we determine their role in ecosystems. In no other system on Earth are we more uncertain about the true diversity of organisms and their roles than in soils. I have examined soil mite (Acari) species at the Konza Prairie Biological Station (KPBS), Kansas, USA, an uncultivated tallgrass prairie, to determine what mechanisms are responsible for their diversity, how alien invasive grasses may impact them, and what role their diversity plays in decomposition. The hypotheses that soil mite species richness, abundance and taxonomic diversity is greater beneath grasses in dicultures (different species) compared to monocultures (same species), beneath grasses of higher resource quality (lower C:N) compared to lower resource quality, and beneath heterogeneous mixes of grasses (C3 andC4 grasses growing together) compared to homogeneous mixes (C3 or C4 grasses) were tested using natural occurrences of grass species as treatments. Increased grass diversity supported a more species and phylogenetically rich soil mite fauna. This relationship was significant at depth but not in the upper soil horizon. Soil mite richness increased nonlinearly with grass species richness suggesting that simple extrapolations of soil faunal diversity based on plant species inventories may underestimate the richness of associated11lsoil mite communities. The proportion of mite size classes in dicultures was considerably different than those for monocultures. These data suggest that interspecific root competition results in increased mite habitat, abundance and diversity. There was no difference in soil mite richness between grass combinations of differing resource quality, or resource heterogeneity. Soil mites sampled beneath six native and one alien-invasive species of grass were similarly abundant, species rich, diverse, and taxonomically distinct. There was no evidence that the community composition of soil mites was specific to grass species or that a significant number of mite species had affinities for different grass species. The soil mite community was weakly related to soil environmental conditions. Only oribatid mites were related to, marginally, the species of grass present. The alien invasive grass species did not support a successionally younger mite fauna and had no influence on mite community structure, possibly because it had not substantially altered the soil environment. Rates of cotton strip decomposition (percent cotton strip tensile strength loss per day, CTSL), and soil mite abundance and species richness were measured at high and low fire frequency sites of the KPBS. Likelihood-based and information theoretic approaches were used to examine strength of evidence in data for models of CTSL representing the Null, Rivet and Redundant hypotheses of biodiversity and ecosystem function (BEF). The Null model including temperature, moisture and saturating effects in the total abundance of predatory mites (Mesostigmata) had more support in the data than any other models. Models representing Rivet and Redundant patterns of BEF settled on parameter values distinct from the Null models but had less support in the data regardless of which mite group was being considered. A significant trend was observed in the models' residuals from low fire frequency sites trends not observed in high fire frequency sites. I speculate that annually burned sites more closely emulate the agricultural system the models were originally designed for than low fire frequency sites, accounting for differences in model performance. Biophysical properties on low fire frequency sites such as increased litter cover, different soil carbon constituents or a different microbial community may regulate decomposition in a manner not accounted for by only soil temperature and moisture driving variables.

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Subject

Konza Prairie Biological Station (Kan.)
Mites -- Kansas
Soil biology -- Kansas

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