Salinity Toxicity due to NaCl has considerable impact on agriculture. Both Na+and Cl–
are toxic and occur in excess where land is exposed to sea water, in many arid
zones and on irrigated land where evaporation exceeds precipitation or irriga-
tion. Declining water tables due to deforestation and intensive agriculture and
resulting salinization are an increasing agricultural problem.
The chief causes of damage by salt are: osmotic stress and dehydration;
inability to regulate stomata (as Na+replaces K+); nutrient ion deficiency; and
Cl–toxicity. Plants show a wide range of salt tolerance, from glycophytes, able
to tolerate small amounts of NaCl, to halophytesable to tolerate ≥500 mM.
Plants able to grow in high salt conditions show a number of adaptations which
are summarized in Table 5.
100 Section G – Sensing and responding to the environment