The effect of Frankia inoculation on growth, mineral nutrition, and N2-fixation of Alnus glutinosa

Frankia symbiosis with Alnus glutinosa improves the growth and nutrition of the host plant. Therefore, the establishment of high N2-fixing activities, active nodule-forming populations of Frankia in soil is desirable. In this study, seedlings of A. glutinosa were inoculated with Frankia isolated from twenty-five root nodules of A. glutinosa in different sites of Guilan province, northern Iran. The seedlings were grown in pots filled with sterilized sand in a green-house. The seedling growth, N2-fixation and nodulation were measured 10 weeks after inoculation. The Inoculated seedling had higher dry weight of shoots, roots and nodules, and nutrients content compared to control. The N2-fixing activity varied from 0.017 to 0.337 mg N mg-1 nodules. The greatest N2-fixing capacity was observed in seedlings inoculated with AG6 Frankia crushed nodules compared with other treatments. There was a significant positive correlation coefficient between nodule dry weight, plant biomass and nutrients contents, that resulted of microbial inoculation effects. The results revealed that introduced Frankia could improve the growth and N2-fixation of A. glutinosa. Thus, selection true sources of inoculums that have a considerable influence to A. glutinosa and optimizing the sustainable production of these inoculums are needed. We concluded that AG6 had a superior effect on A. glutinosa seedlings and can be used for future studies.