Nitrogen fixation symbiosis and salt tolerance of the boreal woody species Elaeagnus commutata

Soil salinity is a major abiotic stress that reduces the growth, survival and physiological functions of most plants. In the boreal forest, elevated levels of NaCl pose reclamation challenges for habitats disturbed by the oil sand industry. The objectives of this study were to determine how salinity affects the nitrogen fixation capability of the native boreal N-fixing shrub, wolf willow (Elaeagnus commutata), as well as to examine how salinity affects its growth and physiology. Seedlings of E. commutata were exposed to 0, 50 and 100 mM NaCl in a hydroponic system and physiological parameters were measured after 1, 4, 8 and 12 weeks of treatment. All plants survived the salinity treatments. Gas exchange parameters including leaf photosynthesis, stomatal conductance and transpiration were only reduced at 100 mM NaCl. In addition, plants showed signs of photosynthetic recovery after 4 weeks. Increasing salinity also led to moderate declines in plant shoot and root growth. While N and K content in plant leaf and root tissues were not reduced by higher salinity, salinity did reduce Ca content in plant leaf tissues. Root nodule function was largely inhibited at 100 mM NaCl, resulting from the absence of nitrogen-fixing vesicles within these nodules. Our data suggested that E. commutata seedlings can survive and grow under up to 100 mM NaCl while maintaining moderate levels of physiological functions, and reduced ability to fix nitrogen, limiting improvements to soil fertility in restoration applications.