Biochemically based models of C 3 photosynthesis can be used to predict that when photosynthesis is limited by the amount of Rubisco, increasing atmospheric CO 2 partial pressure (pCO 2 ) will increase light-saturated linear electron flow through photosystem II (J t ). This is because the stimulation of electron flow to the photosynthetic carbon reduction cycle (J c ) will be greater than the competitive suppression of electron flow to the photorespiratory carbon oxidation cycle (J o ). Where elevated pCO 2 increases J t , then the ratio of absorbed energy dissipated photochemically to that dissipated non-photochemically will rise. These predictions were tested on Dactylis glomerata grown in fully controlled environments, at either ambient (35 Pa) or elevated (65 Pa) pCO 2 , and at two levels of nitrogen nutrition. As was predicted, for D. glomerata grown in high nitrogen, J t was significantly higher in plants grown and measured at elevated pCO 2 than for plants grown and measured at ambient pCO 2 . This was due to a significant increase in J c exceeding any suppression of J o . This increase in photochemistry at elevated pCO 2 protected against photoinhibition at high light. For plants grown at low nitrogen, J t was significantly lower in plants grown and measured at elevated pCO 2 than for plants grown and measured at ambient pCO 2 . Elevated pCO 2 again suppressed J o ; however growth in elevated pCO 2 resulted in an acclimatory decrease in leaf Rubisco content that removed any stimulation of J c . Consistent with decreased photochemistry, for leaves grown at low nitrogen, the recovery from a 3-h photoinhibitory treatment was slower at elevated pCO 2 .
ASJC Scopus subject areas
- Plant Science