Sampling

Mites and collembolans are collected by extracting them from a sample of their soil habitat. Extraction procedures may be either Berlese funnel extraction of soil cores or litterbags, or alternatively, flotation (Bater, 1996). Total microarthropod populations are then estimated by extrapolating from the size of the sample (weight or area) to field dimensions. For sampling protocols and considerations of sampling design, consult Hall (1996), Schinner et al. (1996), Coleman et al. (1999), and Larink (1997).

Soils vary greatly in structure, composition, pore size, moisture regime, and so forth; sampling methods need to be suited to the ecosystem under investigation. Most quantitative samples of microarthropods are taken from soil cores 5-10 cm in diameter by 5-10 cm deep. The smaller cores yield satisfactory results; a 5-by-5-cm core will contain several hundred mites and collembolans. A split core tool with a sharp beveled tip, designed to hold a sleeve for the soil sample, is preferable for most soils (Fig. 9.1). For many soils the great majority of microarthro-pods are found within 5 cm of the surface. In grassland soils and disturbed soils they may be distributed more deeply, and additional 5-cm increments may need to be extracted, to a depth of 15 cm or more. Sample cores should be extracted in a high-efficiency extractor (Fig. 9.2) as soon as possible; storage for any significant period of time will result in lower numbers of microarthropods extracted.

FIGURE 9.1. Soil coring device: (a) outer tube; (b) inner sleeve, typically made of aluminum. Effective core diameter: 5 cm (modified from Gorny and Gram, 1993).
FIGURE 9.2. Design and assembly of the high-efficiency microarthropod extractor (from Crossley and Blair, 1991).
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