Effects of ozone on three open-pollinated families of Pinus taeda L. grown in two substrates

Abstract

Seedlings from three open-pollinated loblolly pine ( Pinus taeda L.) families grown in a mixture of commercial peat moss and grade 3 vermiculite (1:3 by volume) or a mixture of mineral soil and peat (1:1 by volume) were exposed to 0, 160 or 320 ppb ozone (O 3 ) for 6h/day, 4 days/week for 8 weeks beginning 12 weeks after transplanting. Before exposures began, seedlings grown in the vermiculite-peat substrate were taller but smaller in diameter than those grown in the mineral soil-peat substrate. After 8 weeks of exposure, seedlings grown in the mineral soil-peat substrate were significantly larger in diameter and total biomass than those grown in the vermiculite-peat substrate. Primary needle and secondary needle injury increased with increasing O 3 concentrations. Suppression of diameter growth, shoot weight and root weight was linear as O 3 concentration increased. The effect of O 3 on height or diameter growth or shoot biomass was not influenced by substrate type; but the suppression of root biomass due to O 3 was dependent on substrate, with greater suppression in biomass occurring in the vermiculite-peat substrate. Foliar injury due to O 3 was slightly greater in family 8–103, but growth suppression due to O 3 was not significantly different among the families. Based on root biomass, response of seedlings to O 3 was substrate-dependent.