For 400 million years vegetation has been pumping out volatile oxygen to the point of spontaneous combustion causing wildfire. The result is high co2, temperatures and even drought that has to be overcome for survival. Partial opening of the stomas reduces the evaporation of the water on the leaves and so a tree uses less water without any damage to its development. Makes sense to me, remember vegetation has been converting co2 for 3.500 million years
