The lower limit of water availability in soil is known as

The correct answer is D. Wilting point.

The wilting point is the lowest water content in soil at which plants wilt and are unable to recover turgor pressure. It is the point at which plants can no longer absorb water from the soil, and the cells in the leaves begin to collapse. The wilting point is usually determined by measuring the amount of water in the soil after a plant has been allowed to wilt for a certain period of time.

The other options are incorrect.

• Field capacity is the amount of water that a soil can hold after it has been saturated and then allowed to drain for a period of time.
• Hypolimnion is the lower layer of water in a lake or reservoir, which is typically cooler and less oxygenated than the upper layer.
• Thermocline is a layer of water in a lake or reservoir that separates the warmer upper layer from the cooler lower layer.