Elevated CO2 concentration affects vertical distribution of photosynthetic activity in Calamagrostis arundinacea (L.) Roth

Abstract

An understanding of photosynthetic responses to elevated CO2 concentration (EC) across the entire vertical canopy profile will help to achieve more proper simulation of ecosystem responses to expected climate change. Accordingly, we studied changes in vertical gradients of photosynthetic parameters in the grass species Calamagrostis arundinacea under EC at the time of anthesis. Plants were transplanted and grown for 3 years under ambient (385 ppm; AC) and elevated (700 ppm; EC) atmospheric CO2 concentrations in experimental glass domes. In general, EC reduced the variability of photosynthetic activity within the vertical profile of plants. Such changes also altered the differences between AC and EC in the vertical profile. While EC led to greater accumulation of chlorophylls, CO2 assimilation rate, and efficiency of photochemical processes in lower leaves, EC primarily reduced stomatal conductance and transpiration rate in upper leaves. These changes resulted in higher water-use efficiency in lower leaves. On the other hand, we found slightly greater down-regulation of photosynthesis under EC in lower leaves indicated as the A700/A385 ratio. Such knowledge may be important in upscaling EC effects from leaves to the canopy level and modelling impacts of expected climate change on grassland ecosystems.