Interrelations Between Growth and Photosynthesis of Salt Bush (Atriplex Halimus L.) Grown in Saline Media

Abstract

Plants of A. halimus were grown in culture solutions to which NaCl or Na2S04 was added to different concentrations. The osmotic potential of the sap, growth, morphology, and leaf gas exchange (transpiration and photosynthesis) were studied. At least three different effects of salinity were identified: (1) an increase of leaf area and succulence induced by relatively low concentrations of salt in the growth medium. This resulted in an increase of the leaf area available for transpiration and photosynthesis (and hence growth); (2) an increase of stomatal resistance to water vapour loss and C02 uptake. This tended to reduce both transpiration and photosynthesis per unit leaf area; (3) changes in mesophyll resistance to C02 uptake (r;"). Relatively low concentrations of NaCl reduced r;", but high NaCl concentrations (i.e. external osmotic potentials lower than -9 atm) and all concentrations of Na2S04 brought about an increase in r;". In addition to the above effects, salinity may have caused a hormonal imbalance as was indicated by the increased sprouting of lateral buds.