Chlorotic dwarf of eastern white pine caused by an ozone and sulphur dioxide interaction

Perspectives regarding 50 years of research on effects of tropospheric ozone air pollution on US forests

Tropospheric ozone (O(3)) was first determined to be phytotoxic to grapes in southern California in the 1950s. Investigations followed that showed O(3) to be the cause of foliar symptoms on tobacco and eastern white pine. In the 1960s, "X" disease of ponderosa pines within the San Bernardino Mountains was likewise determined to be due to O(3). Nearly 50 years of research have followed. Foliar O(3) symptoms have been verified under controlled chamber conditions. Studies have demonstrated negative growth effects on forest tree seedlings due to season-long O(3) exposures, but due to complex interactions within forest stands, evidence of similar losses within mature tree canopies remains elusive. Investigations on tree growth, O(3) flux, and stand productivity are being conducted along natural O(3) gradients and in open-air exposure systems to better understand O(3) effects on forest ecosystems. Given projected trends in demographics, economic output and climate, O(3) impacts on US forests will continue and are likely to increase.

Foliar injury air pollution surveys of eastern white pine (Pinus strobus L.): A review

A thorough review and critical evaluation of field surveys from 1900 to the present of foliar injury to Pinus strobus L. supposedly caused by air pollution was undertaken. Ninety percent of the surveys failed to meet current scientific standards of acceptability. The conduct and peer review of surveys has been poor and the correct injury symptoms have not always been used. Data were obtained for nine that met screening criteria and injury incidence and severity were mapped. Three fourths of the counties in the natural and planted range of eastern white pine have not been scientifically surveyed, so generalizations regarding large-scale spatial patterns of eastern white pine foliar pathological conditions were not possible. However, recent growth and inventory data indicate that growth throughout the natural range regardless of air pollution or other stresses (e.g. blister rust) is excellent, suggesting that regional performance and foliar conditions are unrelated. Sufficient compelling corroborative evidence was found to conclude that a general decline of eastern white pine throughout its range is not a tenable finding.The putative air pollution sensitivity of eastern white pine appears to be based on studies published between 1963 and 1973 on hypersensitive individuals that are no longer being observed in the field. More recent research on eastern white pine has noted a lack of sensitivity and/or high variability of response. The idea that eastern white pine as a species is highly sensitive to air pollution is no longer supported by the available evidence. However, hypersensitive juvenile individuals comprising no more than 8-9% of the total population may still germinate and grow for a brief period of time (because old enough parent trees are still alive) but soon succumb to current levels of ozone and sulfur dioxide in the environment or are suppressed by tolerant neighbors. This phenomenon has been documented anecdotally and is more aptly called tree decline instead of forest decline. An emerging working hypothesis to explain recent reports of unusual eastern white pine tolerance is that sufficient time has elapsed for tree decline to have occurred leading to a gradual elimination of sensitive genotypes from populations.

Adult toxicity and dominant lethals induced by ozone at specific stages in spermatogenesis in Drosophila virilis

Ozone, a highly reactive three-atom allotrope of oxygen, is formed in high concentrations in various kinds of microenvironments, including electron microscopes, office copy machines, and X-ray devices. Mutagenicity and action modus operandi of ozone suggest its radiomimetic property. In order to test for ozone-induced dominant lethals in Drosophila virilis, we determined that four-hr and longer exposures to 30 +/- 2 ppm ozone were lethal on or before day 25 postexposure. Accordingly, we used a three-hr ozone exposure to investigate dominant lethals induced at specific spermatogenic stages. Ozone increased the percentage of dominant lethals in the stages of spermatogenesis which were investigated. Under the conditions of this experiment, the sperm-sperm bundle stage showed the greatest percentage of dominant lethals induced by ozone. Meiotic cells were the least sensitive to ozone mutagenicity. The induction of dominant lethals is discussed on the basis of chemical reactions from the molecular decomposition of water by radiations and/or ozone. Alternative explanations are presented due to the definition of induced dominant lethals and to associated modifications from ozone exposure.