Potential effects of rising tropospheric concentrations of CO₂ and O₃ on green‐algal lichens

Abstract

SUMMARYParmelia sulcata Taylor was used as a model to examine the efFects of elevated CO.^ and/or O^ on green algal lichens. Tballi were exposed for 30 d in duplicate controlied-environment chambers to two atmospheric concentrations of CO^ ('ambient' [350 /(mol mol '] and 'elevated ' [700 //mol mol"'] 24 h d"') and two O,, regimes ('non-polluted' air [CF, < 5 nmol mol"'] and 'polluted' air [15nmQlmol"' overnight rising to a midday maximum of 75 nmol mol"']). in a factorial design. Elevated CO^ or elevated Oj depressed the light saturated rate of COj assimilation (-4^^,) measured at ambient CO.^ by 30 "" and 18 "", respectively. However, despite this efTect ulfrastrucfura) studies revealed increased Jipid axorage in ce]]s oi the phoEobJonr in response to CO^-enrichment. Simultaneous exposure to elevated O^ reduced CO.,-induced lipid accumulation and reduced -4,^, in an additive manner. Gold-antibody labelling revealed that the decline in photosynthetic capacity induced by elevated CO, and/or O^ 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 ,4^^^ induced by elevated CO., and/or O^ 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 tbat tbe green-algal lichen symbiosis might be influenced by future changes in atmospheric composition. Pbotosynthetic capacity, measured at ambient CO,, was found to be reduced after a controlled 30 d exposure to elevated CO^ and/or O,^ and this efTect was associated with a parallel decline in tbe amount of Rubisco in the pyrenoid of algal chloropiasts.

Photosynthetic carbon acquisition in the lichen photobionts Coccomyxa and Trebouxia (Chlorophyta)

“…In T erici, the highest concentration of Rubisco was found in the pyrenoid even though some gold particles were also present in the stroma (Fig. ID), similar to previous observations of lichenised Trebouxia (Ascaso et al 1995, Balaguer et al 1996. Figure 2A,B shows the photosynthetic CO2 and HCO3 responses of T erici measured at two pH values, 6.2 and 7.9, respectively.…”

“…The data presented here give substantial support to this hypothesis, as judged from the different localisation of Rubisco in the two photobionts (Fig. 1, Ascaso et al , Balaguer et al 1996, the differences in relative requirement and biochemical characteristics of their intemal CA:s (Figs 3 and 7, Hiltonen et al 1995, Palmqvist et al 1995 and the larger intemal DIC pool in Trebouxia (Tab. 1).…”

Effects of Elevated Ozone on Photosynthetic CO2 Exchange and Chlorophyll a Fluorescence in Leaves of Quercus mongolica Grown in Urban Area

“…The concentration of O 3 has been increasing rapidly because of the anthropogenic emissions of several O 3 -forming gases (Katri et al 2006). This increase is expected to continue unabated for the foreseeable future (Luis et al 1996). Many researchers have focused on the effects of O 3 on plants and done work on the mechanism of O 3 induced injury and O 3 resistance of trees (Gian et al 1998;Chantal et al 1999;Paoletti et al 2006).…”

Long-term responses of the green-algal lichen Parmelia caperata to natural CO 2 enrichment

“…Analogous to observations on the response of vascular plants, lichenized green algae have been found to exhibit photosynthetic acclimation when exposed to elevated CO 2 , a phenomenon characterized by a decline in photosynthetic capacity, a marked decrease in the concentration of Rubisco in the algal pyrenoid and an increase in the proportion of the algal cell volume occupied by lipid bodies (Balaguer et al 1996). In nature, photosynthetic acclimation of lichenized algae may be triggered by nutritional constraints since lichens often thrive in nitrogen-de®cient environments (Crittenden et al 1994) and the CCM in lichenized green algae does not improve nitrogen use eciency (Palmqvist et al 1998).…”

“…Lichens containing green-algal Trebouxia species are sensitive to changes in the external concentration of CO 2 (Cowan et al 1992;Balaguer et al 1996), despite the fact that they possess an active CO 2 -concentrating mechanism (CCM; Palmqvist 1993). Analogous to observations on the response of vascular plants, lichenized green algae have been found to exhibit photosynthetic acclimation when exposed to elevated CO 2 , a phenomenon characterized by a decline in photosynthetic capacity, a marked decrease in the concentration of Rubisco in the algal pyrenoid and an increase in the proportion of the algal cell volume occupied by lipid bodies (Balaguer et al 1996).…”