Salinity significantly impairs plant growth primarily by making it difficult for plants to absorb water and by causing toxic effects from accumulated salts.
Excessive salts in the soil severely impact plant health starting with water availability.
The Primary Mechanism: Reduced Water Uptake
High concentrations of salt in the soil decrease the osmotic potential at the root surface. This means the water potential outside the plant roots is lower than inside the roots. As a result, water moves less readily, or in severe cases, can even move out of the roots, leading to reduced water uptake by the plant.
According to the provided information: "Excessive salts in the soil reduce water uptake by plants due to reduced osmotic potential at the root surface. This characterizes the early osmotic stress stage..."
This initial phase, characterized by the difficulty in absorbing water due to external osmotic pressure, is known as the osmotic stress stage.
Consequences for Plant Development
The plant's response to reduced water uptake has cascading effects on its growth and development:
- Stomatal Closure: To conserve limited water, plants close their stomata, the small pores on leaves used for gas exchange (like taking in carbon dioxide).
- Reduced Photosynthesis: Stomatal closure limits CO₂ uptake, which is essential for photosynthesis, the process plants use to create energy and build tissues.
- Reduced Shoot Growth: The combination of water stress, reduced photosynthesis, and potential ion toxicity inhibits cell expansion and division, leading directly to reduced shoot growth.
As the reference states, the osmotic stress stage "...leads to stomatal closure and reduced shoot growth."
Summary of Effects:
| Factor | Effect of High Salinity | Outcome on Plant Growth |
|---|---|---|
| Soil Water Potential | Reduced (lower) | Reduced water uptake |
| Plant Water Status | Decreased | Water stress (Osmotic) |
| Stomata | Closure | Reduced CO₂ uptake |
| Photosynthesis | Decreased | Reduced energy production |
| Shoot Growth | Significantly reduced or stopped | Smaller plants, lower yield |
Beyond osmotic stress, excessive salts can also lead to ion toxicity, where specific ions like sodium (Na⁺) and chloride (Cl⁻) accumulate in plant tissues to toxic levels, further damaging cells and metabolic processes.
Managing salinity often involves improving drainage to leach salts, using salt-tolerant plant varieties, and careful irrigation practices.
