Injury and growth of Jeffrey pine and giant sequoia in response to ozone and acidic mist

Abstract A 2-year study of the interactive effect of sequential exposures of Jeffrey pine ( P. Jeffreyi ) and giant sequoia ( S. giganteum ) to simulated acidic mist and ozone (O 3 ) was conducted in 1985 and 1986. Two-year-old seedlings of each species were exposed to simulated mist acidified to pH 4.1, 3.4, 2.7 or 2.0 with 2:1 HNO 3 /H 2 SO 4 plus appropriate background ions 3 days per week from 0300 to 0600 in outdoor mist exposure chambers. On the same day the same plants were exposed to 0, 0.10 or 0.20 ppm O 3 from 1200 to 1600. Exposures were conducted in May and June of each year. Each O 3 × pH combination contained 12 plants of each species and each treatment was replicated twice. Half the trees were harvested after the first year and the rest after 2 years of exposure to O 3 and simulated acidic mist. In the first year, O 3 at both 0.10 and 0.20 ppm caused light to moderate chlorotic mottle on Jeffrey pine but O 3 had no effect on giant sequoia. Simulated mist at pH 2.0 caused severe foliar necrosis on both species. Ozone had no significant effect on growth of either species in 1985, but simulated acidic mist at pH 2.0 significantly reduced growth of both species. In 1986, similar visible foliar injury symptoms were observed on both species. Ozone significantly reduced leaf, stem and root growth of Jeffrey pine, but growth of giant sequoia was not affected by O 3 . Exposure to simulated acidic mist stimulated Jeffrey pine growth at intermediate pH (3.4 and 2.7) and significantly reduced growth at pH 2.0, relative to growth at pH 4.1. Simulated acidic mist significantly reduced root growth of giant sequoia, particularly at pH 2.0, and the combination of O 3 at 0.20 ppm and mist at pH 2.0 reduced sequoia root growth significantly more than the additive effects of either pollutant acting alone. The effects of both pollutants on root growth were attributed to reallocation of photoassimilates from roots to shoots to maintain growth of photosynthetic tissues.