Role of Genotype in the Response of Loblolly Pine to Tropospheric Ozone: Effects at the Whole-Tree, Stand, and Regional Level
- George E. Taylor *
The interaction between tropospheric ozone (O3) and genotype in loblolly pine (Pinus taeda L.) is explored, focusing on the consequences of different genotypes in a range of basic and applied issues. General conclusions for loblolly pine are: (i) a genetic component underlying phenotypic variation in ozone response is documented at the biochemical, physiological, and whole-plant level; (ii) ozone resistance determined from needle injury is not associated with resistance determined from growth or gas exchange; (iii) mode of inheritance of resistance based on growth is not documented, although evidences point to a multilocus model; (iv) resistance involves avoidance and tolerance mechanisms, and evidence for pleiotropy indicates that resistance carries costs that are important in terms of physiologic ecology and breeding strategies; and (v) breadth of genetically determined variation has consequences for experimental designs, ecological risk assessment, genetic diversity and air quality standards. The threshold for growth effects on average seedlings approaches a 12-h mean concentration of 45 nL L−1, which is below extant air quality in many Southeastern forests. The threshold for sensitive cohorts approaches 25 nL L−1, near the projected concentration a century ago (19 nL L−1). Extant ozone levels are affecting the average loblolly pine intermittently and sensitive cohorts frequently or continuously. The responsiveness of sensitive cohorts is important in understanding how regional stresses will impact ecological resources. Air pollution research in the last decade emphasized the development of exposure-response relationships, centering on selection of statistical indicators of atmospheric ozone. The conclusion that genetic variation is a major source of variation indicates that further improvement in exposure-response relationships will emerge from efforts addressing variability driven by biospheric rather than atmospheric processes.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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