11 - Implications of Stress in Low CO2 Atmospheres of the Past: Are Today's Plants Too Conservative for a High CO2 World?

Abstract

This chapter evaluates various C3-plant processes that are responsive to subambient CO2, particularly those that influence carbon gain and plant growth. It discusses stress × low CO2 interactions, highlighting how subambient CO2 may increase stress frequency and intensity. It explores how selection for stress survival at low CO2 (<200 μmol mo1-1) may constrain plant responses to CO2 enrichment above the current ambient of 365 μmol mo1-1, possibly creating novel stresses associated with excessive carbohydrate accumulation. The primary effect of CO2 on photosynthesis is to modulate the activity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco), the enzyme catalyzing the fixation of CO2 into organic compounds. As a substrate, CO2 availability substantially limits Rubisco activity at atmospheric concentrations below 365 μmol mo1-1 CO2 fixation by Rubisco is also inhibited at CO2 levels below365 μmol mo1-1 by the oxygenation reaction of Rubisco. Rubisco oxygenation leads to photorespiratory inhibition of photosynthesis, with the degree of inhibition rising with increasing temperature and declining CO2.