Interactive effects of elevated temperature and CO(2) on two phylogeographically distinct clones of common reed (Phragmites australis)

The aboveground growth, physiological and biochemical parameters of two clones of the cosmopolitan wetland grass Phragmites australis, grown at four treatment combinations of temperature and CO(2), were investigated to elucidate whether their climate response differed due to inherent differences in their ecological adaptation. The two phylogeographically distinct P. australis clones (DK clone, European genetic background; ALG clone, Mediterranean genetic background) were grown for 151 days in phytotrons at 19/12 °C (day/night temperature) and 390 ppm CO(2), and at elevated temperature (+5 °C) and CO(2) (700 ppm) with treatment factors alone or in combination. The ALG clone had 2–4 times higher aboveground biomass, higher light-saturated rates of photosynthesis (P(max)), maximum electron transport rates (ETR(max)) and Rubisco activity, and higher photosynthetic nitrogen-use efficiency than the DK clone. The DK clone, however, produced more shoots, leaves and side-shoots, and had 9–51 % higher specific leaf area and 15–39 % higher leaf nitrogen concentration than the ALG clone. Although elevated atmospheric CO(2) alone barely affected the aboveground growth of the two P. australis clones, simultaneously elevated temperature and CO(2) stimulated growth and aboveground biomass. Overall, elevated CO(2) stimulated photosynthesis, but the clones responded differently to a concomitant increase in CO(2) and temperature, depending on the phylogeographic background of the plant. The DK clone showed overall stronger responses, and can be considered the more plastic of the two clones with respect to CO(2) and temperature. Thus, the DK clone may be better adapted to climate change than the ALG clone, at least in the short term.