In deep forest understorey, often no more than 1 – 5% of the sunlight available in the canopy reaches leaves. Absorption and reflection by taller plants prevent shorter plants from capturing much of this valuable resource. Without light, there is no carbon gain – and without carbon gain, no growth, or reproduction. What’s a plant to do? Some plants adapt to life in the shade, with thick, dark leaves that are very efficient, capturing nearly all the light available. These leaves also tend to have lower respiration (carbon-loss) rates but lower peak carbon gain rates, resulting in a net increase in carbon gain under low light conditions. But some species have also adapted to sun flecks, where deep shade is suddenly interrupted by a bright fleck of sunlight, as leaves and branches above, perhaps touched by the wind, align perfectly to allow a few minutes of light. Maybe you’ve been walking in the forest when suddenly a glint of the sun becomes visible – it’s the same thing. These plant species are adapted to be able to very quickly upgregulate their photosynthetic performance, using as much of this light as possible. A typical plant will take several minutes to respond to a higher-light environment, but a sunfleck adapted plant may be able to respond much more quickly. It turns out that some plants gain ~80% of their carbon during these rare sunfleck events. There are many ways to make a living!
For more information on sunflecks, take a look at this article.