Effects of ozone and simulated acidic precipitation on ectomycorrhizal formation on loblolly pine seedlings

Abstract

Since air pollutants have been postulated to alter rhizosphere ecology, a study was initiated to evaluate the impact of O 3 and acidic precipitation on ectomycorrhizal formation on loblolly ( Pinus taeda L.) seedlings. Six-month-old loblolly pine from two families differing in O 3 sensitivity were exposed to four O 3 concentrations (charcoal-filtered air, non-filtered, non-filtered × 1.7, or non-filtered × 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 O 3 concentration in the O 3-sensitive family. Elevated O 3 caused a shift in some individual morphotypes in both families. Total number of morphotypes decreased with increasing rainfall acidity in the O 3-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.