| I conducted laboratory incubations of intact soil cores, field studies, and modeling simulations to test the hypothesis that nematode trophic group distributions were related to carbon (Cmin) and nitrogen (N min) mineralization in a sandy loam, old field soil. Microbivorous nematodes may increase microbial Cmin and Nmin and are restricted to water-filled pores with openings greater than their body diameters. If microbivorous grazing controls mineralization, then the distributions of nematode trophic groups should be related to patterns of matric potential and C min and Nmin.; In laboratory incubations in May, August, and November, 1997 and March, 1998, Cmin and Nmin were not coupled at matric potentials of -3, -10, -20, and -50 kPa. Cmin was not related to matric potential. Net Nmin depended on the season, matric potential, microbial biomass and nematode trophic group distributions. Nematodes were present at all matric potentials evaluated, including the tension corresponding to maximum water-filled pore openings (6 mum) smaller than nematode body diameters. Although net Nmin did not increase following incubation at -50 kPa, increases in microbial biomass, respiration per unit microbial biomass, and nematode data suggest that nematode grazing of microbes may be important for nutrient availability in dry soil.; Traditional and spatial statistics, and maps to visualize regional patterns, showed that relationships among soil properties and soil respiration and inorganic N (Ni) under field conditions varied with sampling date (May, August, and November, 1997). Microbivorous nematode numbers were related linearly and spatially to soil respiration and Ni in August, but not in May. In November, nematodes co-occurred with soil respiration in different regions, but did not appear to be related to Ni. Ni was negatively related to microbial biomass N in November.; Spatial patterns of maximum water-filled pore diameters did not coincide with spatial patterns of nematodes, soil respiration, or Ni in any sampling month. However, temporal changes in matric potential which affect maximum water-filled pore diameters may be important for relationships between microbivorous nematodes and soil respiration and Ni.; Results of a four-level food chain model show that trophic interactions among microbivorous nematodes and microorganisms increase soil respiration and Ni. |
