A mechanistic evaluation of photosynthetic acclimation at elevated CO2

Summary Plants grown at elevated p CO 2 often fail to sustain the initial stimulation of net CO 2 uptake rate ( A ). This reduced, acclimated, stimulation of A often occurs concomitantly with a reduction in the maximum carboxylation velocity ( V c,max ) of Rubisco. To investigate this relationship we used the Farquhar model of C 3 photosynthesis to predict the minimum V c,max capable of supporting the acclimated stimulation in A observed at elevated p CO 2 . For a wide range of species grown at elevated p CO 2 under contrasting conditions we found a strong correlation between observed and predicted values of V c,max . This exercise mechanistically and quantitatively demonstrated that the observed acclimated stimulation of A and the simultaneous decrease in V c,max observed at elevated p CO 2 is mechanistically consistent. With the exception of plants grown at a high elevated p CO 2 (> 90 Pa), which show evidence of an excess investment in Rubisco, the failure to maintain the initial stimulation of A is almost entirely attributable to the decrease in V c,max and investment in Rubisco is coupled to requirements.