well no the fungi are not responsible for burning the plant, try and look at it differently...the conditions are right for a higher than normal rate of absorption and this is what is burning the plant. The soil is alive and so are the micro organisms, the type of communication between these living entities isn't something we would understand as communication. And yes there is a discontinuation of the signaling chemicals when the plant no longer needs nutes, there is a delay from when the signals are sent and when they actually stop converting the nutes into a usable form. In that time frame, the plant could get burned. Part of the result of microbial activity is a change in pH. This can greatly effect what can be absorbed and what can not. Even small shifts in pH can take locked up nutes and suddenly make them available in abundance, or suddenly some nutes are locked out and there is too much of something. Best thing to do is flush with pH adjusted water. Shoot for 6.5 to 6.8 pH and 2 to 3x the volume of the container of water. This almost always fixes the problem.