Effect of ozone and aluminum on pitch pine (Pinusrigida) seedlings: anatomy of mycorrhizae

Abstract

Newly germinated pitch pine (Pinusrigida Mill.) seedlings inoculated with a mycorrhizal fungus (Pisolithustinctorius (Pers.) Coker & Couch) were grown for 13 weeks in sand irrigated with nutrient solution (pH 4.0) containing 0, 12.5, 25, or 50 mg/L aluminum (Al) in growth chambers fumigated with 0, 50, 100, or 200 ppb ozone. Anatomical changes in roots stressed by ozone and Al, singly and in combination, were determined by light and electron microscopy. All ozone concentrations reduced the percentage of mycorrhizal colonization. In contrast, Al increased the percentage of colonization at low concentration, reducing it only at the highest level. Aluminum caused more overall deterioration of root cortex than ozone, though both treatments adversely affected the mycorrhizal fungus. Increased vacuolation in the root meristem was caused by both ozone and Al. Additional effects of ozone on cells in the meristem were the swelling of the nuclear membrane and invaginations in the plasmalemma. Intracellular fungal hyphae were observed at the highest level of ozone and (or) Al. The combined effect of ozone and Al on the anatomy of mycorrhizae was greater (possibly synergistic) than the effect of each pollutant alone. Similar cellular alterations have also been observed in forests damaged by pollution.