Effect of NaCl on growth and ion relations in two salt-tolerant strains of Paxillus involutus

The effect of NaCl on growth, biomass and ion relations of two salt-tolerant isolates of Paxillus involutus , MAJ and NAU were investigated. The two Paxillus strains were exposed to the following concentrations of NaCl: 0, 100, 200 and 500 mmol·L −1 . Growth of MAJ and NAU was enhanced by 100 mmol·L −1 NaCl but severely inhibited at the concentration of 500 mmol·L −1 . NAU exhibited a greater capacity to exclude Na + and Cl − under all salinity levels, whereas the salt-includer MAJ had a higher capacity in nutrient uptake under salt stress. The ratios Na + /K + , Na + /Ca 2+ and Na + /Mg 2+ in NaCl-treated MAJ and NAU did not increase at levels of 100 and 200 mmol·L −1 NaCl but markedly increased at 500 mmol·L −1 . This suggests that the two strains, especially MAJ, enhanced nutrient uptake corresponding to the increased Na + influx at moderate salinity. We conclude that both MAJ and NAU are able to tolerate 500 mmol·L −1 NaCl but there are species-specific differences in retaining ionic homeostasis in the two Paxillus strains. NAU is a salt-excluder, MAJ is a salt-includer but retains a high capacity in nutrient selectivity under saline conditions. Their definite mechanisms to enhance salt tolerance of mycorrhizal hosts need further study.