Histological determination of ozone injury symptoms of primary needles of giant sequoia (Sequoiadendron giganteum Bucch.)

Abstract

summaryGiant sequoia (Sequoiadendron giganteum Bucch.) is a unique resource that exists only in groves on the western slopes of the Sierra Nevada in California. Since Sequoia and King's Canyon (SEKI) National Parks are experiencing ozone concentrations phytotoxic to some species of Pinus, we performed several experiments on S. giganteum seedlings to determine the ozone sensitivity of their primary needles and their suitability as sensitive bioindicators during the seedlings stage of growth. Current‐year seedlings were fumigated in open‐top chambers during 1986 and 1987. Treatments included (1) carbon‐filtered air (no ozone); (2) ambient ozone; (3) 1.5 times the ambient amount of ozone; and (4) a no‐chamber treatment. In 1986, ozone doses ranged from 100 to 221 ppm h−1while those in 1987 ranged from 125 to 216 ppm h−1. In neither year did the percentages of plasmolysed cells correlate with ozone dose. In 1986, however, the percentages of amorphously stained and dead cells taken together showed a significant (P= 0.028; r2= 0.721) linear response to dose (y = 29.9 + 0.260x). In the 1987 fumigation, there was no significant relationship between ozone dose and the percentage of either amorphously stained or dead cells. The narrow range of ozone doses (from 125 to 216 ppm h−1) and the short duration of exposure (48 d) may have resulted in high percentages of amorphously stained cells (between 61 and 81 %). In both experimental fumigations, higher ozone doses killed more cells in the needles. When data of the percentages of dead cells from both experiments were pooled, there was a statistically significant (P= 0.0036) correlation coefficient of 0.744 with a line slope of y = 2.472 + 0.051x. There was no evidence of a curvilinear response. The overall anatomy of primary needles from SEKI was similar to that of those sampled from the fumigation experiment; SEKI samples exhibited a high degree of amorphous cell staining (between 67 and 81 %). Cell death averaged 5.1% from all the park samples, a percentage within to the range of cell death (0.9–6.2 %) in the ambient air chambers.