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

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Abstract
Mycorrhizal infection of white pine (Pinus strobus L.) seedlings was measured after 4 months of exposure to simulated acid rain and ozone, applied either alone or in combination. 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 approximately 20% 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 to 0.14 ppm. However, there were significant changes in infection in plants exposed to ozone for 5 days/week. There was no evidence for an interaction between the two pollutants. Percent mycorrhizal infection was highly correlated with seedling nitrogen concentration across all soil types and rain treatments. These observations suggest that increases in available nitrogen may have been largely responsible for the observed effects of acid rain on mycorrhizae.

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