Salt, or salinity, significantly impacts aquatic plants by disrupting essential biological processes. The presence of high salt concentrations in their environment imposes several stresses, primarily affecting their ability to absorb water and nutrients and manage cellular toxicity.
Main Stresses Caused by Salinity
According to the provided reference, salinity directly causes two main types of stress for plants, including those in aquatic environments:
- Osmotic Stress / Water Deficit Stress: When the salt concentration in the surrounding water is higher than inside the plant cells, water tends to move out of the cells. This phenomenon, driven by osmosis, leads to a water deficit within the plant, even though it is submerged in water. The plant struggles to absorb or retain the necessary water for its functions.
- Ionic Stress: High concentrations of specific ions, particularly sodium (Na+) and chloride (Cl−), can be toxic to plants. These ions can accumulate in plant tissues, disrupting cellular functions and processes critical for growth and survival.
The reference states: "The two main, direct stresses caused by salinity to plants are (i) osmotic stress/water deficit stress and (ii) ionic stress [1] (Figure 1)."
Associated Stress: Mineral Nutrient Imbalance
Beyond the direct stresses, salinity leads to an associated problem:
- Mineral Nutrient Imbalance: The presence of high levels of Na+ and Cl− ions interferes with the uptake of essential mineral nutrients from the water or substrate. These ions compete with or block the plant's absorption mechanisms for vital nutrients such as potassium (K+), calcium (Ca2+), and nitrate (NO3−). This nutrient deficiency further weakens the plant and hinders growth.
As noted in the reference: "A third, associated stress is (iii) mineral nutrient imbalance, as Na+ and Cl− interfere or compete with the uptake of mineral nutrients such as K+, Ca2+ and NO3− (Figure 1)."
Summary of Salt Effects
Here's a brief overview of how salt affects aquatic plants:
| Effect | Description | Primary Ions Involved |
|---|---|---|
| Osmotic Stress | Water is drawn out of plant cells due to higher external salt concentration | General salinity level |
| Ionic Stress | Toxicity from accumulation of specific ions | Sodium (Na+), Chloride (Cl−) |
| Mineral Nutrient Imbalance | Interference with uptake of essential nutrients | Na+, Cl− interfere with K+, Ca2+, NO3− |
These combined stresses can severely impact the health, growth, and survival of aquatic plants, often leading to stunted growth, tissue damage, and ultimately, death, depending on the salinity level and the plant's tolerance.
