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

对生长在广岛县大川河河床上的一个天然种群的囊状-丛枝菌根真菌（VAM）的生物量进行了估算。麦角甾醇法测定菌丝生物量。根中麦角甾醇含量随时间增加，8月份达到4.96μg /株。利用外菌丝麦角甾醇浓度和内外生物量比估算，VAM真菌的总生物量为每株30.3mg。VAM真菌生物量约占根系生物量的43%，占土壤有机碳的3.6%。说明VAM真菌生物量是植物吸收碳的一个大库。为了研究施磷量对与纹状体相关的VAM真菌菌丝生物量的影响，在不同施磷水平（0、0.1、1、5、10mgP kg^<-1>土壤）的土壤中生长60 d。5和10mgP kg^<-1>时，根内菌丝生物量显著下降，而外菌丝生物量无显著变化。我们还研究了生长在大川河河流坝中的三种柳属植物的菌体状态。田间生长的植株被VA和/或外生菌根真菌定植。但在盆栽试验中未发现VA菌根定殖对植株生长的直接影响。

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.