Population energetics of bacterial-feeding nematodes: Carbon and nitrogen budgets

Bacterial-feeding nematodes participate in nitrogen mineralization in decomposition food webs to an extent determined by metabolic and behavioral attributes, by life history, and by the relative C-to-N ratios of the nematodes and their bacterial prey. The mean C-to-N ratio for eight nematode species cultured on Escherichia coli on agar was 5.89 (range 5.16-6.83). The mean C-to-N ratio was similar, although with greater variability among species, when nematodes were cultured in soil on a range of soil bacteria. The mean C-to-N ratio of five isolates of soil bacteria and E. coli was 4.12 (range 3.65-4.92). Where food was not limiting, production-to-assimilation ratios ranged from 0.58 to 0.86 and respiration-to-assimilation ratios from 0.14 to 0.42. The excess N assimilated during growth and egg production, and the excess N assimilated to meet the C needs of respiration, were similar across species at 20 degrees C. The excess N from both sources provides an estimate of the amount of N excreted by each nematode during the life course. The weight of bacteria necessary to meet the growth and respiration costs at 20 degrees C ranged from 0.87 mu g mu g-nematode(-1) d(-1) for Cephalobus persegnis to 1.99 mu g mu g-nematode(-1) d(-1) for Bursilla labiata, providing estimated consumption rates between 6.61 x 10(5) and 15.22 x 10(5) bacterial cells mu g-nematode(-1) d(-1). At a field site, we estimate that the bacterial-feed. nematode community in the top 15 cm soil mineralized N at rates increasing io 1.01 mu g-N g-soil(-1) d(-1) in rhizosphere soil. On a monthly basis, the community contributed 0.28 kg-N ha(-1) in April, 0.98 kg-N ha(-1) in May and 1.38 kg-N ha(-1) in June in bulk soil. Contributions in the rhizosphere would be considerably greater depending on the ratio of rhizosphere to bulk soil. The contribution of individual species to N mineralization in the rhizosphere varied through the first 3 months of the summer growing season as a function of their abundance and their metabolic and development rates in relation to temperature. Rhabditis cucumeris was the predominant contributor in April; there were similar contributions by Acrobeloides bodenheimeri, B. labiata, Cruznema tripartitum, and R. cucumeris in May; A. bodenheimeri and B. labiata were the major contributors in June. (C) 1997 Elsevier Science Ltd.