Halotolerant fungi stimulate growth and mitigate salt stress in Alnus glutinosa Gaertn.

Soil salinity is an important abiotic stress factor that reduces both plant growth and development and decreases diversity and metabolic potential of microorganisms, particularly fungi. However, some fun- gal isolates, including mycorrhizal fungi, can increase tolerance of plants to salinity, e.g. by activation of de- fense mechanisms. Main aim of our study was: (i) to identify and characterize fungal strains isolated from fruitbodies growing at saline test sites and (ii) to determine the effect of fungal inoculation on the growth and salinity tolerance of Alnus glutinosa Gaertn. seedlings. Two ectomycorrhizal strains (Amanita muscaria OW-10 and Paxillus involutus OW-5) and a saprotrophic one (Gymnopus sp. OW-6) were isolated from fruit- bodies collected at naturally saline test sites. The plant growth promotion was observed after inoculation of plants with the ectomycorrhizal fungus – P. involutus OW-5, while the use of Gymnopus sp. OW-6, displaying the highest hydrolytic activity, decreased seedling growth parameters. Moreover, P. involutus OW-5 (char- acterized by characterized by medium salt tolerance salt tolerance) promoted growth of black alder in the presence of salt, while A. muscaria OW-10 (with the highest salt tolerance) increased fresh and dry mass of seedlings only in the absence of salt. Black alder seedlings inoculated with P. involutus OW-5 revealed higher synthesis of proline in aboveground organs compared to the control plants which suggested that accumulation of this compound can be a mechanism protecting black alder seedlings against salt stress. In conclusion, we recommend the use of P. involutus OW-5, which displayed the best plant growth promoting ability and salt tolerance, for inoculation of black alder trees used in reclamation of saline habitats