"Shade avoidance" is not shade!
This is the most common misconception whenever I talk about this topic. So let's start there. I think most peple intuitively understand that if a plant is in the shade, it'll grow differently. Plants need light to photosynthesize and grow normally, so if something is blocking the light, plants will alter their growth to 'find' the sun.
Shade (or lack of light) changes the way plants grow.
But today, we're not talking about shade; we're not decreasing the amount of light that plants are getting.
Today, we're talking about a thing plants can do to *avoid* being shaded. They do this in *anticipation* of being shaded. This is why we call it 'shade avoidance'.
Plants - like everything else - reflect light. They reflect a lot of green light, and that's why we perceive them as green.
Plants also reflect light outside our visible spectrum. A particular wavelength of light that plants reflect, we're going to call "far-red" light. Plant leaves reflect a LOT of far-red light.
Plants *absorb* lots of red light (they use the visible red wavelengths for photosynthesis).
So light reflected from plant leaves has a very low ratio of red light to far-red light (R:FR).
The R:FR light ratio is an important environmental cue for lots of plant responses - flowering, germination, others. But we're going to focus on just the shade avoidance bit. There's a lot of previous research about this topic, that I'm not going to present. We're going to focus mostly on sugar beet (Beta vulgaris), because it is the crop I study most.
Sugar beets, the plant we study, can't really grow tall. And sacrificing roots is a problem since that's the part of the plant we harvest. So if you expose a sugar beet plant (or other beets like garden beets) to the low R:FR from neighboring plants, the results are pretty devastating to root yield. Here's the first study we published on this topic. The bottom line: having plants nearby sugar beet reduced root yield by 70%!
In this study, if the weeds were present from sugar beet emergence until the beets had 2 true leaves (a couple weeks after emergence), then sugar beet root biomass was reduced by 32%. In fact, a majority of the total yield lost in this study was due to just that first couple weeks of weed exposure.
Even if you go control the weeds after they've been there a couple weeks, our data suggests you can't recover that lost yield potential.
Andrew Kniss
Jon Sullivan
Dream Bigly
cbud