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 precip itation on ectomycorrhizal formation on loblolly (Pinus taeda L.) seed lings. Six-month-old loblolly pine from two families differing in O3 s ensitivity were exposed to four O3 concentrations (charcoal-filtered a ir, 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 exclus ion tubes designed to isolate individual root systems. Roots were eval uated for the presence or absence of ectomycorrhizal short roots. Ecto mycorrhizae were quantified as numbers of morphotypes or morphotype ti ps per centimeter-long root. Total number of morphotypes per centimete r-long root increased with increasing O3 concentration in the O3-sensi tive family. Elevated O3 caused a shift in some individual morphotypes in both families. Total number of morphotypes decreased with increasi ng rainfall acidity in the O3-sensitive family, but was not altered in the other family. The responses observed in this study are probably r elated to changes in host metabolism and/or shifts in individual morph otypes.