If you live near the coast, you know certain plants can't thrive near the ocean. Some types of grasses may not be able to put up with the salt that gets blown inland by the sea spray. Trees and shrubs often face similar difficulties. Other plants do just fine. Knowing salt and its effects on cells is key to understanding what effect salt water has on plants.
Osmosis is the process by which water gets into plants. Plant roots have structures that make it very easy for water to permeate and thus get used by the plant. However, in most plants, these structures do not have the same reaction to salt water. The salt water permeates more slowly and may even draw moisture from the roots. Therefore, one of salt water's most severe effects is that it can rob a plant of water.
If the plant takes in salt water, the salt may eventually build up in the cellular structure of plants. While all living things need at least some amount of salt, too much can be detrimental. The salt then interferes with other chemical reactions in the plant, causing the plant to not produce the energy it needs to survive.
A study on maize in the "Brazilian Journal of Plant Physiology" found that some plants had reduced amounts of potassium and other nutrients, which shows salt affected not only the plant cells, but how those cells received nutrients. Those plants with nutrient deficiencies experienced stunted growth and other problems compared to the control group. However, the report also showed some plants had a greater natural resistance to salt.
If osmosis interference, cellular interference and nutrient deficiency happen for prolonged periods of time, the plant will likely suffer. Stunted growth or growth that does not look as full as it should is evidence the plant is under stress. In the most severe cases, death may result.
Though there are very few things you can do if salt water is a problem in your area, some plants are better adapted to it than others. Some even have defenses against the salt. These plants are called halophytes. Some have special glands that expel salt. Some store salt in their leaves, then drop them at the end of each growing season. Other halophytes even have membranes on their roots that allow water in, but keep salt out.