Summary: Plant and Soil 212: 7583, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Grazing in a porous environment: 1. The effect of soil pore structure on C
and N mineralization
Josef H. Görres1,, Mary C. Savin1, Deborah A. Neher2, Thomas R. Weicht2 and Jos´e A.
1Soil Ecology and Microbiology Laboratory, The Greenhouses, University of Rhode Island, Kingston, RI 02881,
USA and 2Department of Biology, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA
Received 6 October 1998. Accepted in revised form 6 May 1999
Key words: enclosure, grazing, nematodes, nutrient mineralization, porous environment
The porous soil environment constrains grazing of microorganisms by microbivorous nematodes. In particular, at
matric potentials at which water-filled pore spaces have capillary diameters less than nematode body diameters
the effect of grazing, e.g. enhanced mineralization, should be reduced (`exclusion hypothesis') because nematodes
cannot access their microbial forage. We examined C and N mineralization, microbial biomass C (by fumigation-
extraction), the metabolic quotient (C mineralization per unit biomass C), nematode abundance, and soil water
content in intact soil cores from an old field as a function of soil matric potential (-3 to -50 kPa). We expected,
in accordance with the exclusion hypothesis, that nematode abundance, N and C mineralization would be reduced
as matric potential decreased, i.e. as soils became drier. N mineralization was significantly greater than zero for