Huh. I hope for 77°F when I didn't have much light. Which I can see in the vegetative room, there's no sense in blasting it with the maximum amount of μmol m⁻² s⁻¹ you possibly can when they are too small to use all that energy. But I've looked at a couple studies which seemed to show that a decent-sized cannabis plant cannot use as much light-energy at that temperature as it can at 86°F (that's all assuming ambient CO₂ levels - if you're supplementing to ~800 PPM, then the same plant ought to be able to use more light-energy - at a slightly higher temperature).
IDK, to be honest. The above would depend on other things being optimum. Specifically, the plant would have to be able to transpire all the moisture that it "wanted to" (please forgive me ascribing consciousness to a plant, my mind is in the low part of its cycle and wresting the proper words from it is a challenge), the xylem in good shape (I won't say "healthy," lol because it's made from dead cells), the Casparian strip undamaged (generally not an issue), the stomata clean (no smoking in the grow rooms
)... I suppose that if the mineral content of the soil/nutrient solution is too high, it could interfere with osmosis at the root level - but one would surely notice that. Good airflow to evaporate the transpired moisture - and to provide a cooling affect
at the plant. Adequate moisture levels in the soil would be assumed. Oh, and if you're using some kind of surfactant to lower the surface tension of the water/solution, that would tend to throw a monkey wrench in the system, because it sort of depends on the adhesion and cohesion properties of water to work correctly in the first place.
Oh... and having typed all that, lol, if your strain's natural environment is a cool one (Swiss strains, maybe?), then "YMMV" applies. Come to think of it, it almost always does, regardless of the discussion
.
I'm rambling again (whodathunkit?). I just... you know... I stuck a piece of tape on my laptop above the display and wrote "
ON-TOPIC!!!" on it :rolleyes3 .