Water use and sodium chloride uptake by apple trees

SummaryApple trees (Malus sylvestris Mill.cv. ‘Granny Smith’) were grown with divided root systems and were exposed to combinations of soil salinity (90 meq 1−1) and partial soil oxygen deficiency (waterlogging) in half root zones to simulate three of the conditions in which these combinations of double stress may occur in the field.Whenever a salinity stress was applied to a root zone, water uptake from that root zone was depressed to approximately 50% of normal levels while water uptake from the non-saline root zone increased by 50% over normal. If a low oxygen stress was superimposed upon the salinity stress, water uptake declined even more (to 30% of normal) and uptake in the non-stressed zone increased proportionately (to 60% above normal non-stress levels). When an oxygen stress was applied to one root zone and a salinity stress to the other, water uptake in the saline zone again dropped by 50% under normal but uptake increased by only 30% in the non-saline zone. With one saline root zone and both root zones waterlogged water uptake dropped to 30% in the zone with the double stress but there was no increase in water uptake from the non-saline oxygen stressed zone.Exposure of a half root zone to salinity resulted in chloride concentrations in the roots increasing 5-fold compared with the non-saline zone. However, the chloride was retained in the roots and not transported to the leaves so that leaf chloride concentrations were not significantly different from non-salinized plants. When a plant was exposed to a waterlogged saline solution in one half root zone, leaf chloride concentration increased more than 4-fold over initial concentration if the other rootzone was not waterlogged and when both saline and non-saline root zones were waterlogged, leaf chloride concentration increased almost 7-fold over initial concentrations. Any exposure of roots to NaCl stress resulted in significantly higher root Cl than occurred in non-salinized roots.