Pergamon Soil Bid. Bidrent. Vol. 27. No. 3, pp. 319-330. 1995 003%0717(94)00186-3 Copyright I<] 1995 Ekvier Science Ltd Printed in Great Britain. All rights reserved 003870717/95 $9.50+0.00 POPULATION ENERGETICS OF BACTERIAL-FEEDING NEMATODES: RESPIRATION AND METABOLIC RATES BASED ON CO2 PRODUCTION H. FERRIS, S. LAU and R. VENETTE Department of Nematology, University of California, Davis, CA 95616, U.S.A zyxwvutsrqponmlkjihgfedcba (Accepted 25 Ju1.v 1994) Summary-By grazing on bacteria, bacterial-feeding nematodes participate in decomposition food webs and N mineralization to an extent determined by metabolic and behavioral attributes and by life history. We studied the respiratory and metabolic activities of 8 speciesof bacterial-feeding nematodes at 5 temperatures by measuring the rate of CO2evolution with an IR gas analyzer. We developed a method for determining size- or stage-specific respiration rates from measurements made on populations of varied stage-structure. Species from a single field site exhibited different thermal optima and temperature-niche breadths for respiratory and metabolic activity. Respiration rates of adults ranged between 1.25-8.80 nlO2 h-’ at 20°C among the species. Metabolic rates of adults ranged from 1.15 nl O2 pg(fresh wt)-’ h-’ for Rhabditis cucumeris Andrassy to 4.43 nl 02 pg(fresh wt)-’ h-’ for Bursilla labiata Andrassy at 20°C. At each temperature, metabolic rates of nematodes of similar size varied with thermal adaptation of the species. Metabolic rates of Cruznema tripartitum Zullini and Cephalobus persegnis Bastian were more sensitive to temperature change than were those of Acrobeloides bodenheimeri Thome, A. buetschlii Steiner and Buhrer and Panagrolaimus detritophagus Fuchs. C. persegnis exhibited the greatest total metabolic activity across a range of temperatures, and P. detritophagus the least. Observed differences in thermal adaptation may contribute to the predominance of species in the nematode community at different times during the year or at different depths in the soil. INTRODUCTION Metabolic and respiratory energetics of soil-inhabiting nematodes have been studied for populations of several species (e.g. Bair, 1956; Klekowski ef al., 1972, 1974, 1979; Nicholas, 1975; De Cuyper and Vanfleteren, 1982; Schiemer, 1982, 1983). In many cases, assessments have been based on O2consumption rates of adult nematodes using the Cartesian Diver method. Data are often based on one or a few individuals and usually at 20°C [e.g. as summarized in Klekowski et al. (1972) for 68 species]. Carbon budgets for soil nematodes have been developed by trophic level assignment of nematodes recovered from soil samples at the study site (Sohlenius, 1979; Persson et al., 1980; Sohlenius et al., 1988). In those studies, general relationships between temperature and respiration rate per unit weight of nematode are assumed to apply to all nematodes in the system. Also, C utilization in respiration is inferred from O2 consumption, which requires assumptions of respiratory quotients. Although data are available for several nematode species (Klekowski et al., 1972) identification of species of bacterial-feeding ne- matodes from field soil samples is an arduous task, so classification to trophic groups allows systems-level estimates of C utilization by nematodes. However, our preliminary data on individual nematode species from a single field site indicate differences in metabolic rates and in the response of respiration rates to temperature (Ferris and Lau, 1992). Since individual species predominate at different times of the year, higher resolution estimates of bacterial-feeding nematode participation in C flow may not be possible from trophic level groupings. The extent to which an organism participates in energy flow in an ecosystem is a function of population size, individual and population growth rates, and metabolic activities of individuals. Our objectives were: (i) to measure the effect of temperature on metabolic activity of 8 species of bacterial-feeding nematodes, as indicated by CO? evolution rates; and (ii) to provide coefficients for the relationships between metabolic or respiration rates and temperature for juvenile and adult stages of these nematodes. MATERIALS AND METHODS The 8 nematode species studied are representatives of 3 families of the order Rhabditida: Acrobeloides bodenheimeri Thorne, A. buetschlii Steiner and Buhrer and Cephalobus persegnis Bastian (family Cephalo- bidae); Bursilla labiata Andrassy, Caenorhabditis elegans Dougherty, Cruznema tripartitum Zullini and Rhabditis cucumeris Andrassy (family Rhabditidae); and Panagrolaimus detritophagus Fuchs (family Panagrolaimidae). Other than C. elegans, all species were endemic in the field site of a long-term low-input sustainable agriculture experiment at the University of 319