Ethylene production by different age class ponderosa and Jeffery pine needles as related to ozone exposure and visible injury

Summary Ethylene produced by different needle age classes representing natural populations of two ponderosa pine varieties [Pinus ponderosa var. arizonica (Engelm.) Shaw and var. ponderosa Dougl. ex Laws.] and Jeffery pine (Pinus jeffreyi Grev. and Balf.) was characterized using mercuric perchlorate traps. All populations contained individual trees which were either symptomatic or asymptomatic with respect to visible ozone injury. Ethylene production by different needle age classes was also characterized in P. ponderosa var. ponderosa seedlings grown in open top ozone fumigation chambers. Older age class needles produce significantly (P>0.05) more ethylene than younger age class needles. Needles of both P. ponderosa var. ponderosa and P. jeffreyi exhibiting ozone injury in the field produced significantly (P>0.05) higher levels of ethylene than asymptomatic conspecific trees. Seedlings exposed to the highest level of ozone in the fumigation study produced the highest levels of ethylene, followed by fumigation with medium and low ozone concentrations and carbon filtered air. These data indicate that the measurement of ethylene in conifer needles, as a measure of stress, needs to be calibrated for needle age class. It also suggests that the sensitivity of a tree to ozone injury may be regulated by the inherent ability of the individual to produce ethylene.