Stomatal limitation of photosynthesis and reduced growth of the halophyte, Plantago maritima L., at high salinity

Abstract

Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m−3 NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m−3 NaCl was only 20% of that in plants at low salinity. Both the Na+ and K+ content of leaves and roots increased with external salinity. There was no change in the Na+/K+ ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na+ ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO2 and by ribulose‐1,5‐bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO2 concentration. The increased stomatal limitation of photosynthesis resulted in higher water‐use efficiency of plants grown at high salinity.