Early interactions between arbuscular mycorrhizal fungi and Frankia during colonisation and root nodulation of Alnus glutinosa

Abstract

Glasshouse experiments showed significant differences in early interactions of Alnus glutinosa with five different arbuscular mycorrhizal species and Frankia. Thirty and 60 days after inoculation of roots with AMF alone, colonisation was highest with Glomus hoi and G. mosseae followed by Gigaspora rosea. Lowest colonisation was with Acaulospora scrobiculata and Scutellospora castanea. In associations with AMF resulting in relatively low colonisation, e.g. S. castanea, plant biomass after 60 days was higher than in un-inoculated controls but when inoculated with Frankia also was equal to controls. In contrast, the biomass of plants with high levels of AMF colonisation e.g. with G. hoi, was equal to the controls when alone but was lower in dual symbiosis with Frankia. This effect was particularly marked 30 days after inoculation. There was also a depressive effect of nodulation on plant biomass 30 days after dual inoculation that was less apparent after 60 days. This effect was most marked for AMF giving rise to the highest levels of colonisation (G. hoi and Gi. rosea). The data suggest that in dual inoculated alder seedlings, inhibitory effects on early growth can result, possibly from competition with micro-symbionts for resources such as photosynthates. However, effects may only be temporary, to be relieved as seedlings develop a larger shoot system with greater photosynthetic capacity