title: Stable isotope composition (δ(13)C and δ(15)N values) of slime molds: placing bacterivorous soil protozoans in the food web context.
abstract: BACKGROUND
  Data on the bulk stable isotope composition of soil bacteria and bacterivorous soil animals are required to estimate the nutrient and energy fluxes via bacterial channels within detrital food webs. We measured the isotopic composition of slime molds (Myxogastria, Amoebozoa), a group of soil protozoans forming macroscopic spore-bearing fruiting bodies. An analysis of largely bacterivorous slime molds can provide information on the bulk stable isotope composition of soil bacteria.
  
  
  METHODS
  Fruiting bodies of slime molds were collected in a monsoon tropical forest of Cat Tien National Park, Vietnam, and analyzed by continuous-flow isotope ratio mass spectrometry. Prior to stable isotope analysis, carbonates were removed from a subset of samples by acidification. To estimate the trophic position of slime molds, their δ(13) C and δ(15) N values were compared with those of plant debris, soil, microbial destructors (litter-decomposing, humus-decomposing, and ectomycorrhizal fungi) and members of higher trophic levels (oribatid mites, termites, predatory macroinvertebrates).
  
  
  RESULTS
  Eight species of slime molds represented by at least three independent samples were 3-6‰ enriched in (13) C and (15) N relative to plant litter. A small but significant difference in the δ(13) C and δ(15) N values suggests that different species of myxomycetes can differ in feeding behavior. The slime molds were enriched in (15) N compared with litter-decomposing fungi, and depleted in (15) N compared with mycorrhizal or humus-decomposing fungi. Slime mold sporocarps and plasmodia largely overlapped with oribatid mites in the isotopic bi-plot, but were depleted in (15) N compared with predatory invertebrates and humiphagous termites.
  
  
  CONCLUSIONS
  A comparison with reference groups of soil organisms suggests strong trophic links of slime molds to saprotrophic microorganisms which decompose plant litter, but not to humus-decomposing microorganisms or to mycorrhizal fungi. Under the assumption that slime molds are primarily feeding on bacteria, the isotopic similarity of slime molds and mycophagous soil animals indicates that saprotrophic soil bacteria and fungi are similar in bulk isotopic composition.
authors.affiliation: A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, 119071, Moscow, Russia.
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Tiunov
authors.affiliation: A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, 119071, Moscow, Russia.
authors.forename: Eugenia E
authors.initials: EE
authors.lastname: Semenina
authors.affiliation: Moscow State Lomonosov University, Faculty of Biology, 119234, Moscow, Russia.|The Russian-Vietnamese Tropical Scientific and Technological Centre, Southern Branch, Ho Chi Minh, Vietnam.
authors.forename: Alina V
authors.initials: AV
authors.lastname: Aleksandrova
authors.affiliation: A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, 119071, Moscow, Russia.|The Russian-Vietnamese Tropical Scientific and Technological Centre, Southern Branch, Ho Chi Minh, Vietnam.
authors.forename: Sergey M
authors.initials: SM
authors.lastname: Tsurikov
authors.affiliation: A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, 119071, Moscow, Russia.|The Russian-Vietnamese Tropical Scientific and Technological Centre, Southern Branch, Ho Chi Minh, Vietnam.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Anichkin
authors.affiliation: V.L. Komarov Botanical Institute of the Russian Academy of Sciences, 197376, St. Petersburg, Russia.|The Russian-Vietnamese Tropical Scientific and Technological Centre, Southern Branch, Ho Chi Minh, Vietnam.
authors.forename: Yuri K
authors.initials: YK
authors.lastname: Novozhilov
mesh_terms: D001419:Bacteria; D018533:Biomass; D002247:Carbon Isotopes / Q000032:analysis*; D020387:Food Chain; D048690:Fruiting Bodies, Fungal / Q000737:chemistry; D009235:Myxomycetes / Q000737:chemistry* / Q000502:physiology*; D009587:Nitrogen Isotopes / Q000032:analysis*; D012987:Soil / Q000469:parasitology*; D012988:Soil Microbiology
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D012987:Soil