Thanks for link! I found this very interesting. Underlines added:
"Finally, the refractometer can also provide an indication of
boron levels in your crop. If the brix levels of your crop do not drop overnight, then you may have uncovered a serious boron deficiency.
Early each evening, a trapdoor opens, which allows the transfer of glucose in the chloroplasts down to the roots. 60% of this sugar lode is then exuded from the roots to feed the army of organisms in the rhizosphere (root zone). The opening of that important doorway is governed by boron. The absence of the "door opener" means that sugar is trapped in the leaves and the workforce beneath the roots is effectively starved of energy. The wheels begin to fall off shortly after that. Regular monitoring with your refractometer can prevent this boron-based problem and the resilience of your crop and soils will improve. Remember that the universal law "give and you will receive" is at work at the nexus of photosynthesis, the most important process on the planet. Brix monitoring can identify when and why the "giving" has ceased and you will be empowered to fast-track your response (i.e., foliar spray 1 kg of Solubor with 1 kg of pre-mixed
NTS Soluble Humate Granules™)."
I'm wondering if the movement of nutrients down to the roots is dependent on still having enough light. Would it help the plant to have light intensity decrease near EOD rather than just 100% to pitch black?