Chlorophyll and carotenoid concentrations in two varieties of Pinus ponderosa seedlings subjected to long-term elevated carbon dioxide

Abstract

Two varieties of ponderosa pine (Pinus ponderosa Dougl. var. scopulorum (Rocky Mountain variety) and P. ponderosa var. ponderosa (Sierran variety)) seedlings were subjected to elevated atmospheric CO₂ for two and a half years. The CO₂ concentrations were ambient, ambient + 75 μl l⁻¹, ambient + 150 μl l⁻¹ and ambient + 300 μl l⁻¹, or approximately 350, 425, 500 and 650 μl l⁻¹ CO₂. After one and a half years of exposure to elevated CO₂ and until the end of the study, seedlings of both varieties showed symptoms of stress including mottling, mid-needle abscission and early senescence. In both varieties, exposure to CO₂ concentrations greater than ambient + 75 μl l⁻¹ resulted in lower chlorophyll a, chlorophyll b and carotenoid concentrations. At elevated CO₂ concentrations, the concentrations of pigments in needles of the Sierran variety were lower than those in the Rocky Mountain variety. Also, at elevated CO₂ concentrations, the pigment concentrations in the 1-year-old needles of both P. ponderosa varieties were lower than those in current-season needles.