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Exposing Loblolly Pine Seedlings to Acid Precipitation and Ozone: Effects on Soil Rhizosphere Chemistry

USDA-FS, 3041 Cornwallis Road, P.O. Box 12254, Research Triangle Park, NC 27709;

F. C. Thornton

TVA, Muscle Shoals, AL 35660;

A. E. Tiarks

USDA-FS, Pineville, LA 71360;

B. G. Lockaby^*, A. H. Chappelka and R. S. Meldahl

School of Forestry, M. White Smith Hall, Auburn University, AL 36849-5418.

^* Corresponding author.

ABSTRACT

Rhizosphere and nonrhizosphere soils were sampled in association with the roots of field-grown, l-year-old loblolly pine (Pinus taeda L.) that had been exposed to simulated acidic precipitation and O₃ treatments. Soil samples adjacent to roots and from the bulk soil were analyzed separately for H, Al³, Ca², and Mg² concentrations. For the acid precipitation treatment, H levels were significantly greater in the rhizophere compared with the bulk soil, but no clear trend could be attributed to acidic precipitation levels. Hydrogen ion concentrations associated with the O₃ levels, at times, differed significantly by treatment, butnot between rhizosphere and bulk soil. Rain pH and ₃ level produced no statistically significant distinction between rhizosphere and nonrhizosphere soil for Al³, Ca², or Mg². However, after combining rhizosphere and nonrhizosphere soil samples, Al³ concentrations were found to generally increase as rain pH decreased, whereas Ca² and Mg² followed the opposite pattern. No such pattern for O₃ level was apparent. Significant interactions between acid precipitation and O₃ treatments were not detected.