Population- and ecosystem-level effects of predation on microbial-feeding nematodes

  • Laakso J
  • Setälä H
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We studied the role of nematode predation in the functioning of detrital food webs assembled in mi- crocosms. The microcosms contained defaunated humus and litter materials, a diverse microbial community with bacteria, fungi and protozoa, and a birch (Betula pend- ula) seedling infected with mycorrhizal fungi. Different levels of top-down control upon microbivorous nema- todes were set up by assembling food webs either with- out predators, or in combinations with a specialist and a non-specialist predatory mite (Mesostigmata). The nematode community was composed of either (1) three species of bacterivorous, or (2) three species of fungi- vorous nematodes or (3) both groups together. After two growing periods for the birch (38 weeks), the mi- crocosms were destructively sampled for animal and microbial biomasses, concentration of mineral N in the soil, plant biomass and plant N concentration. The specialist predator reduced biomasses of both bacterial- and fungal-feeding nematodes by more than 50%, whereas the non-specialist predator weakly increased the biomass of fungivorous nematodes. Thus, under high predation pressure, the biomass of microbivores chan- ged as predicted by trophic dynamic models assuming strong top-down control and uniformly behaving trophic levels. Despite this, microbial biomass was unaffected by the predators. However, microbial respi- ration increased slightly in the presence of predators. Assuming that microbial respiration correlates with microbial productivity, the increase in microbial respi- ration indicates a cascading productivity regulation. The composition of the microbivore community had only a minor effect on the outcome of the top-down control on microbes. The > 50% reduction in nematode biomass and respiration coincided with < 16% increase in mi- crobial respiration and did not affect microbial biomass. J. Laakso (21) · H. Setala University of Jyvaskyli, Department of Biological and Environmental Science, PO Box 35, FIN-40351, Jyvaskyla, Finland e-mail: jotla@jyu.fi, Fax: + 358-14-602321 Presence of the specialist predator slightly reduced soil NH' concentration in communities with fungivore nematodes but plant growth and N uptake remained unchanged. Thus, the structure of the community only weakly controlled nutrient mineralisation

Author-supplied keywords

  • Detrital food web
  • Energy channels
  • Mesostigmatid mites
  • Microbivorous nematodes
  • Nutrient cycling

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  • Jouni Laakso

  • Heikki Setälä

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