Gas exchange and growth responses of ectomycorrhizal Picea mariana, Picea glauca, and Pinus banksiana seedlings to NaCl and Na2SO4

Black spruce (Picea mariana), white spruce (Picea glauca), and jack pine (Pinus banksiana) seedlings were inoculated with Hebeloma crustuliniforme or Laccaria bicolor and subjected to NaCl and Na2SO4 treatments. The effects of ectomycorrhizas on salt uptake, growth, gas exchange, and needle necrosis varied depending on the tree and fungal species. In jack pine seedlings, ectomycorrhizal (ECM) fungi reduced shoot and root dry weights and in the ECM white spruce, there was a small increase in dry weights. Sodium chloride treatment reduced net photosynthesis and transpiration rates in the three studied tree species. However, NaCl-treated black spruce and jack pine colonized by H. crustuliniforme maintained relatively high photosynthetic and transpiration rates and needle necrosis of NaCl-treated black spruce seedlings was reduced by the ECM fungi. Higher concentrations of Na+ were found in shoots compared with roots of the three examined conifer species. ECM fungi reduced the concentrations of Na+ mainly in the shoots and this reduction was greater in plants treated with NaCl compared with Na2SO4. Shoots contained generally higher concentrations of Cl- compared with roots. In the NaCl-treated black spruce and white spruce, both ECM species significantly reduced Cl- concentrations. Our results point to overall greater phytotoxicity of NaCl compared with Na2SO4 and support our earlier findings which demonstrated beneficial effects of ECM fungi for woody plants exposed to NaCl stress.