RELATIONSHIPS OF SOIL MICROARTHROPOD BIOMASS WITH ORGANIC-MATTER AND PORE-SIZE DISTRIBUTION IN SOILS UNDER DIFFERENT LAND-USE

Soil microarthropods were sampled every 3 months for ly at 10 sites in the northern Netherlands, varying in soil type and land use. Microart hropods were divided into seven functional groups and biomass-C ha(-1) was calculated for the top 10 cm soil layer. The four quantitatively principal functional groups were: cryptostigmatic mites; non-cryptosti gmatic mites; predatory mites; and omnivorous collembola. Possible rel ationships between the mean annual biomass of these groups and soil ty pe, land use or soil organic matter were studied. Microarthropod bioma ss was larger in sandy soil than in loamy and generally larger in mead ows than in wheat fields; the mineral layer of forest soils being inte rmediate. Non-cryptostigmatic mite, omnivorous collembola and predator y mite biomass showed strong positive correlations. Cryptostigmatic mi te biomass correlated with lower organic matter input quality, while o mnivorous collembola and non-cryptostigmatic mites showed a positive c orrelation with the amount of input. Omnivorous collembola were negati vely affected by a discontinuous input of organic matter to the soil. We found relationships between functional group biomass and either soi l organic matter density fractions or soil pore size distribution only when the grassland sites were analyzed separately. Both analyses show ed correlation patterns for cryptostigmatic mites to deviate from thos e of the other three main functional groups. Cryptostigmatic mites sho wed a positive correlation with the lightest organic matter density fr action, while the non-cryptostigmatic mites and omnivorous collembola were correlated to the heavier fractions. The cryptostigmatic mites co rrelated with the 6-90 mu m pore size class, while the other three gro ups Showed strong correlation to the 1.2-6 mu m, as well as the larges t (>90 mu m) pore size class. Both observations lead to the conclusion that omnivorous collembola and non-cryptostigmatic mites are related to fungal growth (in the largest pores and on the heavy organic matter fraction), while the cryptostigmatic mites show a more saprovorous fe eding mode. (C) 1997 Elsevier Science Ltd.