Measurement of myhcelial biomass of vesicular-arbuscular mycorrhizal fungi in natural ecosystems

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The biomass of vesicular-arbuscular mycorrhizal (VAM) fungi was estimated in a natural population of Kummeroiwia striata growing in the riverbed of the Otagawa River in Hiroshima Prefecture. The ergosterol analysis was employed to determine the mycelial biomass. Ergosterol content in the roots increased with time to 4.96μg per plant in August. Total biomass of VAM fungi, estimated using the ergosterol concentration in the external mycelia and the internal/external biomass ratio, was 30.3mg per plant. The VAM fungal biomass accounted for about 43% of root biomass and 3.6% of soil organic carbon. It was suggested VAM fungal biomass is a large sink of carbon assimilated by plants in the plant community.To clarify the effect of P supply on the mycelial biomass of VAM fungi associated with K. striata, the plant was grown in soils at different P application levels (0, 0.1, 1, 5, 10mgP kg^<-1> soil) for 60 days. Internal mycelial biomass in roots decreased significantly at 5 and 10mgP kg^<-1>, whereas no significant change in the external mycelial biomass was detected.We also examined the mycorrizal status of three Salix species growing in the fluvial bar of the Otagawa River. The plants growing in the field were colonized by VA and/or ectomycorrhizal fungi. However, the direct effect of VA mycorrhizal colonization on the plant growth was not detected in the pot culture experiment.