Final answer:
Plants wilt in dry soils at higher temperatures because the water potential of the soil is lower than the plant, making water uptake difficult, and plants close stomata to conserve water, resulting in wilting.
Step-by-step explanation:
When temperatures increase, the demand for water within a plant goes up because of escalated transpiration rates. However, if the soil is dry, it possesses a lower water potential than the plant. This means that there is a more negative water potential gradient between the soil and the air, rather than between the soil and the plant roots, making it harder for the plant to draw water from the dry soil. Therefore, under drought conditions, plants wilfully close their stomata to conserve water, and may even shed leaves to survive. Sustained inability to obtain water causes plants to wilt due to the lack of turgor pressure in their cells.
In summary, when soil water potential is very low due to dry conditions, plants struggle to absorb water, leading to wilting because cells cannot maintain pressure to keep structure, and plants close stomata to minimize water loss.