Do plants suffer transpiration loss when the temperature is below the dew point?

Question

When plants absorb carbon dioxide, they lose water (transpiration). At a given level of water content in the air, the air is saturated below a particular temperature (dew point). So, if a plant's stomata are open and it is absorbing carbon dioxide from the air, does it lose any water to the air, when the temperature is below the dew point?

Answer 1

Yes some plants keep their stomates open at night so will transpire through the evening dewpoint (during the warm season the lowest dewpoint temperature occurs mostly in the evening due to the longer day). Since the guard cells are also regulated by cell turgor they will close if the water loss becomes to great.

Actually plant opening or closing their stomata at night has a direct affect on the dewpont temperature. The stomata on a corn plant close overnight blocking transpiration. By not adding water to the air the dewpoint will fall by several degrees by morning. However this is not seen over plants like wheat that keep their stomata open at night. Wheat continues to transpire moisture into the atmosphere causing the dewpoint temperature to fall less overnight in spring.
The dewpoint is further altered by soil evapotranspiration adding to the air's moisture. This means summer dewpoints can vary between as little as 1 and 2 degrees Fahrenheit during the Midwest's summer.

Cacti only open their stomata at night when they lose less water by avoiding the high daylight temperatures. In the desert Southwest sometimes dew points are in single digits or even negative. The lower the dewpoint the less water in the air but cacti will still lose less to the cold, dry night than the hot, dry day.

Answer 2

The temperature often falls decrease than the dewpoint. Cloud, fog, frost and dew are the consequence because of the fact the surplus water vapour condenses or deposits into water droplets or ice crystals. The dew factor then falls with the temperature.