The actinorhizal shrub, Myrica cerifera L., is widespread in coastal areas where it may be exposed to variable saline conditions. In growth chamber studies, 5-month-old seedlings remained viable during exposure to 150 mM NaCl for 35 d, though concentrations above 50 mM significantly depressed plant and root nodule growth. Concentrations of NaCl above 50 mM also depressed stomatal conductance to water vapour diffusion and net photosynthetic rates. Relative to control plants, nitrogenase activity per g dry weight of nodules decreased for 21 d in plants subjected to a range of NaCl concentrations. By day 35. plants exposed to 25 and 50 mM NaCl had recovered some nitrogenase activity relative to the controls, whereas plants receiving 100 and 150 mM had not. At 35 d, plants treated with 150 mM NaCl had a rate of N2 fixation per g dry weight of nodule tissue 26% of that in control plants. However, no mortality had occurred, and full recovery followed the conclusion of the experiment. Thus, although periodic natural increases in salinity from sea spray or storm overwash may not lead to plant mortality, growth and N2 fixation will be significantly decreased in M. cerifera.
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