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EFFECTS OF CARBON DIOXIDE AND OZONE ON NITROGEN RETRANSLOCATION IN PONDEROSA PINE NEEDLES
Citation:
Olszyk, D M., D T. Tingey, AND W E. Hogsett. EFFECTS OF CARBON DIOXIDE AND OZONE ON NITROGEN RETRANSLOCATION IN PONDEROSA PINE NEEDLES. Presented at 5th International Symposium on Responses of Plant Metabolism to Air Pollution and Global Change, Pulawy, Poland, November 1-4, 2001.
Description:
Changes in leaf N concentration can be an important response to air pollutants in trees, with implications both for tree growth and N cycling through forest ecosystems. Ozone causes premature leaf senescence, which may be associated with a shift in N from the senescing leaves to other leaves or organs of the tree, and/or a loss of N from the needles to the litter layer. Elevated CO2 usually produces lower leaf N concentrations, which may be associated with movement of N to other parts of the plant and/or dilution of leaf N due to increased weight or area of the leaves. The joint effects of CO2 and O3 on leaf N are uncertain.
Ponderosa pine seedlings were grown for three years in outdoor, sunlit chambers that maintain natural variability in climatic and edaphic factors, using an unfertilized forest soil. The seedlings were exposed to CO2 and O3 in a 2 x 2 factorial design experiment with one of four treatments: ambient or elevated (ambient + 200 ppb) CO2, with low or high O3. During the second and third growing seasons of the study, both current and previous year cohorts of leaves were sampled before and after the period of maximum late summer needle senescence. Nitrogen concentrations (and concentrations of Ca, P and other elements as indicators for changes in other nutrients) were measured for leaves on the trees and leaves which had senesced.
We present N and other elemental concentrations in the Ponderosa pine leaves, and indicate how those concentrations are affected by elevated CO2 and high O3. We also indicate how those concentrations are influenced by leaf senescence, leaf age and season. The results are evaluated in terms of the effects of CO2, O3 and the other factors on the potential retranslocation of N from leaves, and the possible impacts on tree growth and N cycling through the ecosystem.