what kinds of things can cause harm to the mycorrhizae in a plants roots? do they need to have a food source added to the soil to survive?
Have you read this thread yet? http://forum.grasscity.com/organic-growing/976433-mycorrhizal-fungi-myths-truths.html
yes. it did not really specify beyond potential issues with trichoderma... I was wondering more about which chemicals cause harm. for instance I know that hydrogen peroxide will kill them. it also does not mention what the mycorrhizae feed on and/or what should be added to the soil for that purpose.
Excessive phosphorus (P) in soil is most harmful to mycorrhizal fungi. You'll get the most benefit from using a VAM product if soil P levels are < 50 ppm. The higher the P levels in a soil, the less effective a VAM product will be. From this site : http://mycorrhizas.info/vam.html