What factors decrease the rate of transpiration in leaves?

Answer 1

1) Moist surroundings - Decrease Concentration gradient and thus rate of diffusion

2) Cold Surroundings - Decrease rate of diffusion

3) Pitted Stomata - Increase distance of diffusion and act as a 'buffer zone', meaning the water has to pass through many concentration gradients of slowly increasing levels before it has diffused out.

And finally, saving the best until last,

4) Closing the stomata altogether - stops any water diffusing out.

Answer 2

Cooling of a plant results in the metabolism of the plant slowing down, this in turn reduces the demand for food and nutrients and the amount of water that is required to sustain the plant.

Extremely high temperatures. Studies on certain plants have shown that at high temperatures certain plants again slow their metabolism and even enter a state of near "suspended animation" in an effort to reduce stress on the plant. At temperatures approaching 40 degrees C, many plants simply switch off (unless they are specifically adapted to high temperature environments), slower metabolism again results in lower usage of nutrients and water.

High humidity. High humidity levels around a plant (particularly the leaves) prevent transpiration occurring at an elevated rate. In areas of extreme humidity water vapour is in fact absorbed into the plant through the stoma instead of being lost by them.

On an evolutionary timescale (talking about hundreds or thousands of generations) plants would adapt to use less and less water, as succulents and other xerophytes have done - thicker cuticle, reflective leaf surfaces, smaller leaves etc.

Answer 3

sunken stomata, curling of a leave, trichomes (hairs like structures that grow on the surface of the leaves)