First-year results on the effects of elevated atmospheric CO2 and O3 concentrations on needle ultrastructure and gas exchange responses of Scots pine saplings.

Abstract

The effects of realistically elevated O and CO concentrations on the needle ultrastructure and photosynthesis of ca. 20-year-old Scots pine ( L.) saplings were studied during one growth period in open-top field chambers situated on a natural pine heath at Mekrijärvi, in eastern Finland. The experiment included six different treatments: chamberless control, filtered air, ambient air and elevated O, CO and O + CO. Significant increases in the size of chloroplast and starch grains were recorded in the current-year needles of the saplings exposed to elevated CO These responses were especially clear in the saplings exposed to elevated O + CO concentrations. These treatments also delayed the winter hardening process in cells. In the shoots treated with O, CO and combined O + CO the P was decreased on average by 50% (ambient CO) and 40% (700 ppm CO). Photosynthetic efficiency was decreased by 60% in all the treated shoots measured under ambient condition and by 30% in the CO and O + CO treated shoots under 700 ppm. The effect of all the treatments on photosynthesis was depressive which was probably related to evident accumulation of starch in the chloroplasts of the pines treated with CO and combined O + CO. But in O treated pines, which did not accumulate starch in comparison to pines subjected to ambient air conditions, some injuries may be already present in the photosynthetic machinery.32Pinus sylvestris32322323232max222322323