When Maximum Photosynthesis Happens

Surprisingly enough, it is not on those cloudless, sunny days. Plants actually do best (and take up the most carbon for you carbon-o-philes out there) on bright cloudy days or hazy days, when the sunlight is diffuse instead of concentrated on just a few leaves, leaving the rest in shadow. That's one of the reasons they grow great roses in Seattle, and the rain forests are so productive. Here's a reference for this, and for the unexpected result of a volcanic eruption (more carbon uptake): Roderick M, Farquhar G, Berry S, and Noble I, On The Direct Effect of Clouds and Atmospheric Particles on the Productivity and Structure of Vegetation, Oecologia, 129(1), September 2001. There are a LOT more references than this, but the abstract of this one is pretty understandable, and viewable free at the Springerlink site. So plant out your seedlings on these bright cloudy days with confidence, knowing that their little leaves will be working hard to build new plant growth.