Habitat responses of fossil plant species to palaeoclimate - Possible interference with CO2?

In this study, the potential effects of a changing CO2 level on photosynthesis performance under simultaneously changing water availability and temperature is evaluated by using a model based on optimized gas exchange, including different scenarios of photosynthesis regulation that may result from evolutionary adaptation. The results illustrate the impact of changing CO2 on water and temperature demands under these various conditions, indicating 1) a particularly substantial influence of CO2 under low CO2 (< 380 ppm); 2) for higher levels of CO2 (> 380 ppm) a decreasing influence under further increasing CO2, and 3) the relevance of possible evolutionary adaptation of the photosynthetic machinery to a changing CO2 level. Downregulation of photosynthesis, for instance, leads to a distinctly enhanced response of gas exchange to increasing CO2, particularly under low to moderate levels (180 ppm-380 ppm). Changes in atmospheric CO2 therefore adds an additional source of uncertainty to those already considered for NLR based methods. It may, however, also offer new possibilities for palaeoecophysiological research.