In hydroponics we seek to emulate and improve the growing conditions for our beloved ladies... In nature ground temperature fluctuates at a very slow pace... therefore I would conclude that as long as the reservoir changed temperatures slowly you are fine... i.e. put in many small bags on a perpetual cycle (so put in one wait two hours put in another wait two hours put in another wait put in a nother wait.... take the first on out & put one in then wait, take the second one out and put one in... and so on) This would drive ME crazy though... why are your res temps so high?
The only things I found within the scientific community about root zone temperatures had to do with pathogenic microlife and parasites if its too high (80+) and no water uptake if its too low (freezing haha).
This is the only thing I could find that says temperature locks out nutrients... in this case Nitrogen. However the plant did not show any changes.. so thats good right.
http://eco.confex.com/eco/2010/techprogram/P25809.HTM