Hi everyone. I have been chatting on another forum, and a fellow poster has asked a question I found interesting and don't know the answer to. Why is it that WLD does not affect outdoor plants. If it is 5C outside, why don't leaves drop in the sun? Why does WLD only seem to affect plants indoors? Does the temperature of the leaves make any difference? If anyone could answer, and if anyone has any links backing up WLD I would be really grateful! Thanks in advance, Dan.
I have wondered about this too. I don't have the answer but I wonder if wind plays a role. When the sun shines on leaves indoors the leaf temperature can rise significantly above the air temperature which causes the leaves to transpire more. Outdoors, wind might prevent the leaf temperature from rising as much. In addition, I have read that wind will cause the leaf stomata to close which should reduce transpiration. From another forum The environment can profoundly affect transpiration rate (water loss from the leaves). Water loss from the tree is greatly increased by high daytime temperatures, and on days of low atmospheric humidity. In a light breeze, air movement draws extra moisture from the leaf's stomata. However, in a strong wind, when leaves are vigorously shaken, the stomata close and water loss (transpiration) stops. Interestingly, if a person manually shakes their tree vigorously, the stomata will close and transpiration stops. - Millet Jim
In addition to humidity and wind, there are a other differences I can think of between indoor trees in containers and outdoor trees in the ground that may influence WLD. 1. The outdoor trees have a larger root system to draw water from. 2. The leaf temperature for indoor trees in a temperature controlled room is always higher or the same as the root temperature unless the roots are heated. For outdoor trees, the leaf temperature is higher than the root temperature during the day but lower than the root temperature at night. Maybe the night temperatures allow some water recovery.
