How do plants cope with shade?

By John Upton

Plants can tell when they have germinated in the shade of their competitors. Neighboring leaves absorb most of the red and blue wavelengths from the sun but reflect the far-red wavelengths. A preponderance of waves of light at the far-red end of the spectrum, compared with the intensity of light that’s more readily visible to humans, warns a plant that it’s going to need to fight to survive.

Plants growing in the shade can fight to survive by adopting one of two strategies: They can try to avoid the shade, or they can adapt to it.

Shade avoidance is the more common strategy, especially in grasslands and in other habitats where most of the plants grow to roughly the same height. To escape the shade, a plant using this strategy will prioritize the growth of its stem over its roots and over its leaves, most of which will be grown high along the stem, in a bid to stretch itself into the sun’s nourishing rays.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

That’s according to Dutch researchers, writing in the February issue of Trends in Plant Science. But the scientists point out that precious little is known about how plants pursue the alternative strategy of shade adaptation. They argue that specific additional research is needed to help explain how some plants, such as shrubs that grow in forests, have adapted to shady environments. There are indications that these specialized plants tolerate shade by regulating levels of certain proteins and hormones, and by suppressing the plant kingdom’s normal instinct to spend lots of energy to grow out of the shade.

“Analysis on pairs of shade and non-shade species could provide information,” the scientists, led by Charlotte Gommers and Ronald Pierik of Utrecht University, wrote in their paper. “To investigate shade tolerance fully, we will need to venture outside our genetic models.”

Better understanding shade tolerance wouldn’t just fuel cocktail party chatter among ecophysiologists — it could help to increase the amount of food available around the world. If scientists could train crops to develop shade adaptation strategies, then those crops would be expected to invest more energy into growing harvestable yields, such as juicy cobs of corn, instead of unnecessarily wiry stalks.

“This might lead towards crop varieties which, when grown in high density, do not invest in undesirable shoot elongation, but do adapt their shaded, lower strata of the vegetation for more efficient photosynthesis.”

Yosemite National Park
Shade avoidance is common in meadows, grasslands and in other habitats where most plants grow to the same height; Shrubs growing in forests often adopt shade tolerance strategies / John Upton