Responses of mycorrhizal jack pine (Pinus banksiana) seedlings to NaCl and boron

In earlier studies, we established that mycorrhizal associations protect plants against salt stress. However, elevated boron levels are often present in saline soils and little is known about the effects of boron on salt resistance of mycorrhizal plants. In the present study, we inoculated jack pine (Pinus banksiana) seedlings with Hebeloma sp., Suillus tomentosus and Wilcoxina mikolae var. mikolae to study the effects of mycorrhizal associations on seedling responses to boron and salt. Seedlings were grown in the greenhouse and subjected to 60 mM NaCl, 2 mM H3BO3 or 60 mM NaCl + 2 mM H3BO3 treatments for 4 weeks. Dry weights, shoot:root ratios and chlorophyll concentrations were higher in inoculated seedlings for all treatments compared with the non-inoculated plants. When applied with NaCl, B aggravated needle necrosis while reducing Cl concentrations in shoots of non-inoculated plants. Plants treated with 2 mM H3BO3 + 60 mM NaCl had similar concentrations of Na and B to those that were treated separately with 60 mM NaCl and 2 mM H3BO3. Plants inoculated with mycorrhizal fungi had lower shoot Na concentrations compared with non-inoculated seedlings, but showed relatively little impact from elevated B concentrations.