Water potential in leaf tissue is 'positive' (near zero ) during

Options

A. Low transpiration
B. Excessive transpiration
C. Guttation
D. All of the above .

Answer

**Step-by-Step Solution:**

1. **Understanding Water Potential**: Water potential is a measure of the potential energy of water in a system, which influences the movement of water. It is typically expressed in units of pressure (megapascals, MPa) and can be positive or negative.

2. **Components of Water Potential**: Water potential (Ψ) is influenced by two main components:
- **Solute Potential (Ψs)**: This is usually negative because the presence of solutes lowers the water potential.
- **Pressure Potential (Ψp)**: This can be positive or negative depending on the pressure exerted on the water.

3. **Conditions Affecting Water Potential**:
- In general, pure water has a water potential of zero (Ψ = 0).
- When there are more water molecules in a system (like during low transpiration), the water potential can be higher (closer to zero or positive).
- Conversely, during high transpiration, water is lost from the leaf, leading to a decrease in water potential (more negative).

4. **Analyzing the Options**:
- **Low Transpiration**: During low transpiration, there is less water loss from the leaf, leading to a higher concentration of water molecules in the leaf tissue. This results in a positive or near-zero water potential.
- **Excessive Transpiration**: This would lead to a loss of water, resulting in a more negative water potential.
- **Guttation**: This is the process where water is expelled from the leaves, usually occurring at night when transpiration is low. This can also lead to a positive water potential.

5. **Conclusion**: The correct answer to the question is that water potential in leaf tissue is 'positive' (near zero) during **low transpiration**.

**Final Answer**: Low transpiration.

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