Effects of ozone and acid rain on white pine (Pinus strobus) seedlings grown in five soils. II. Mycorrhizal infection

Increasing rain acidity consistently reduced the number of mycorrhizal short roots. In general, infection decreased linearly versus rain pH. Plants exposed to simulated rain at pH 3.0 had c20% fewer mycorrhizal roots than plants exposed to pH 5.6 rain. The decrease in the number of mycorrhizal roots was a result of decreases both in the number of short roots available for infection and in the percentage of roots infected. Ozone had no effect on mycorrhizal infection if applied 3 alternate days/week at concentrations ranging from 0.02-0.14 ppm, but there were significant changes in infection in plants exposed to ozone for 5 days/wk. There was no evidence for an interaction between the 2 pollutants. Percent mycorrhizal infection was highly correlated with seedling N concentration across all soil types and rain treatments. -from Authors