How do tropical plants transpire if the humidity is 100% most of the time?
Relative humidity becomes 100% only on clouds when dew point reaches maximum and this causes rain fall from clouds. So plants are not in 100% RH and hence transpiration never stops. Transpiration is both evapo transiration and evaporation may stop, not transpiration which is active biological process. Humidity is a measure of the amount of water vapor dissolved in the air, not including any liquid water or ice falling through the air. For clouds to form, and rain to start, the air does have to reach 100% relative humidity, but only where the clouds are forming or where the rain is falling from. This normally happens when the air rises and cools. Typically, rain falls into air with less than saturated humidity.
