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Potential Effects of Rising Tropospheric Concentrations of CO2 and O3 on Green-Algal Lichens
Luis Balaguer, Fernando Valladares, Carmen Ascaso, Jeremy D. Barnes, Asuncion de Los Rios, Esteban Manrique and Elizabeth C. Smith
The New Phytologist
Vol. 132, No. 4 (Apr., 1996), pp. 641-652
Stable URL: http://www.jstor.org/stable/2558883
Page Count: 12
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Parmelia sulcata Taylor was used as a model to examine the effects of elevated CO2 and/or O3 on green algal lichens. Thalli were exposed for 30 d in duplicate controlled-environment chambers to two atmospheric concentrations of CO2 (`ambient' [350 μmol mol-1] and `elevated' [700 μmol mol-1] 24 h d-1) and two O3 regimes (`non-polluted' air [CF, < 5 nmol mol-1] and `polluted' air [15 nmol mol-1 overnight rising to a midday maximum of 75 nmol mol-1]), in a factorial design. Elevated CO2 or elevated O3 depressed the light saturated rate of CO2 assimilation (Asat) measured at ambient CO2 by 30% and 18%, respectively. However, despite this effect ultrastructural studies revealed increased lipid storage in cells of the photobiont in response to CO2-enrichment. Simultaneous exposure to elevated O3 reduced CO2-induced lipid accumulation and reduced Asat in an additive manner Gold-antibody labelling revealed that the decline in photosynthetic capacity induced by elevated CO2 and/or O3 was accompanied by a parallel decrease in the concentration of Rubisco in the algal pyrenoid (r = 0.93). Interestingly, differences in the amount of Rubisco protein were not correlated with changes in pyrenoid volume. Measurements of in vivo chlorophyll-fluorescence induction kinetics showed that the decline in Asat induced by elevated CO2 and/or O3 was not associated with significant changes in the photochemical efficiency of photosystem (PS) II. Although the experimental conditions inevitably imposed some stress on the thalli, revealed as a significant decline in the efficiency of PS II photochemistry, and enhanced starch accumulation in the photobiont over the fumigation period, the study shows that the green-algal lichen symbiosis might be influenced by future changes in atmospheric composition. Photosynthetic capacity, measured at ambient CO2, was found to be reduced after a controlled 30 d exposure to elevated CO2 and/or O3 and this effect was associated with a parallel decline in the amount of Rubisco in the pyrenoid of algal chloroplasts.
The New Phytologist © 1996 New Phytologist Trust