Effects of sodium chloride salinity on root growth and respiration in oak seedlings

Root and shoot biomass of oak seedlings were reduced after 9 days of watering with a nutrient solution containing either 50 or 250 mM NaCl. Both moderate and high salinity treatment strongly altered root elongation. In contrast, specific respiration of roots was unaffected by the moderate salinity treatment while it was reduced by 62 % after 9 days of watering with a nutrient solution containing 250 mM NaCl. Na+ content strongly increased in all plant tissues with increasing NaCl concentration in the nutrient solution. Na+ contents in leaves and in twigs were lower than in roots at 50 mM NaCl in the nutrient solution while they were similar at 250 mM. Prevention of Na+ translocation in shoot in moderately stressed oak probably requires extra energy, which may be provided by an increase in maintenance respiration. At higher salinity (250 mM), root respiration was strongly inhibited, which might explain the inability of severely stressed oak seedling to prevent Na+ translocation to the shoot. An increase in the respiratory cost for maintenance, for active ion transport and/or for growth processes in oak root encountering sodium chloride salinity is therefore consistent with the occurrence of a high rate of root respiration while growth rate was reduced. ((C) Inra/Elsevier, Paris.).