The growth and nitrogen fixation of Caucasian alder (Alnus subcordata C.A.Mey) that inoculated with Frankia were investigated in pots filled with sterilized sand. The Frankia suspensions prepared from root nodules of A. subcordata that isolated from 25 different sites of Hyrcanian forest, northern Iran. The seedling growth, N2-fixation and nodulation were measured 10 weeks after inoculation. Dry weight of shoots, roots and nodules, and N content ofthe seedlings inoculated with Frankia were higher than those without inoculation. The greatest impact on the nitrogen xing ability, microbial inoculation effects and plant biomass was observed in seedlings inoculated with AS50 Frankia crushed nodules compared with other treatments. The results of these experiments showed that the Frankia crushed nodules could improve the growth and nitrogen xation of A. subcordata. Thus, selection true sources of inoculums that have a considerable influence to A. subcordata and optimizing the sustainable production of these inoculums is needed.Key word: Alnus subcordata, Frankia, Growth, N2-fixation

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