EFFECTS OF OZONE AND SIMULATED ACIDIC PRECIPITATION ON ECTOMYCORRHIZAL FORMATION ON LOBLOLLY-PINE SEEDLINGS

Since air pollutants have been postulated to alter rhizosphere ecology, a study was initiated to evaluate the impact of O3 and acidic precipitation on ectomycorrhizal formation on loblolly (Pinus taeda L.) seedlings. Six-month-old loblolly pine from two families differing in O3 sensitivity were exposed to four O3 concentrations (charcoal-filtered air, non-filtered, non-filtered x 1.7, or non-filtered x 2.5) and three levels of rainfall acidity (pH = 3.3, 4.3, 5.3) in modified open-top chambers for one growing season. Seedlings were planted in root exclusion tubes designed to isolate individual root systems. Roots were evaluated for the presence or absence of ectomycorrhizal short roots. Ectomycorrhizae were quantified as numbers of morphotypes or morphotype tips per centimeter-long root. Total number of morphotypes per centimeter-long root increased with increasing O3 concentration in the O3-sensitive family. Elevated O3 caused a shift in some individual morphotypes in both families. Total number of morphotypes decreased with increasing rainfall acidity in the O3-sensitive family, but was not altered in the other family. The responses observed in this study are probably related to changes in host metabolism and/or shifts in individual morphotypes.