Growth and root system development of white oak and loblolly pine as affected by simulated acidic precipitation and ectomycorrhizal inoculation

Abstract

Individual and interactive effects of simulated acidic rainfall and ectomycorrhizal inoculation on growth of white oak ( Quercus alba L.) and loblolly pine ( Pinus taeda L.) were examined. Seedlings of each species inoculated with basidiospores of Pisolithus tinctorius (Pers.) Coker and Couch and uninoculated control seedlings were exposed to two simulated rains per week of pH 4.8, 4.2 or 3.6, for 26 weeks. After the exposures, mycorrhizal quantification of complete root systems revealed that ectomycorrhizal development, whether by P. tinctorius on inoculated seedlings or by naturally occurring fungi on control seedlings, was greater on loblolly pine treated with the most acidic of the simulated development was greatest on loblolly pine treated with the most acidic of the simulated rains, there was no consistent effect of increasing acidity on mycorrhizal development of white oak. Diameter growth of white oak and height and diameter growth of loblolly pine were significantly increased by the P. tinctorius infection. Within both mycorrhizal treatments, exposure to rains of pH 3.6 significantly reduced the diameter growth of white oak, but rainfall acidity had little effect on the growth of loblolly pine. Of the variables examined, the data presented here suggest the primary effect of acid precipitation on white oak seedlings is on shoot diameter, whereas its primary effect on loblolly pine seedlings is on mycorrhizal development.