Shade tolerance

In ecology, shade tolerance refers to a plant's ability to tolerate low light levels. The term is also used in horticulture and landscaping, although in this context its use is sometimes sloppy, especially with respect to labeling of plants for sale in nurseries.

Shade tolerance is a relative term, a complex, multi-faceted property of plants, not a single variable or simple continuum. Different plant species exhibit different adaptations to shade. In fact, a particular plant can exhibit varying degrees of shade tolerance, or even of requirement for light, depending on its history or stage of development.

Except for some parasitic plants, all plants need sunlight to survive. However, in general, more sunlight does not always make it easier for plants to survive. In direct sunlight, plants face desiccation and exposure to UV rays, and must expend energy producing pigments to block UV light, and waxy coatings to prevent water loss.

Plants adapted to shade have the ability to utilise far-red light (about 730 nm) more effectively than plants adapted to full sunlight. Most red light gets absorbed by the shade-intolerant canopy plants, but more of the far-red light penetrates the canopy, reaching the understory. The shade-tolerant plants found here are capable of photosynthesis using light at such wavelengths.

The situation with respect to nutrients is often different in shade and sun. Most shade is due to the presence of a canopy of other plants, and this is usually associated with a completely different environment—richer in soil nutrients—than sunny areas.

Shade-tolerant plants are thus adapted to be efficient energy-users. In simple terms, shade-tolerant plants grow broader, thinner leaves to catch more sunlight relative to the cost of producing the leaf. Shade-tolerant plants are also usually adapted to make more use of soil nutrients than shade-intolerant plants.

...
Wikipedia