Growth in elevated CO2 can both increase and decrease photochemistry and photoinhibition of photosynthesis in a predictable manner. Dactylis glomerata grown in two levels of nitrogen nutrition
2001
Hymus, G.J. | Baker, N.R. | Long, S.P.
Biochemically based models of C3 photosynthesis can be used to predict that when photosynthesis is limited by the amount of Rubisco, increasing atmospheric CO2 partial pressure (pCO2) will increase light-saturated linear electron flow through photosystem II (Jt). This is because the stimulation of electron flow to the photosynthetic carbon reduction cycle (Jc) will be greater than the competitive suppression of electron flow to the photorespiratory carbon oxidation cycle (Jo). Where elevated pCO2 increases Jt, 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) pCO2, and at two levels of nitrogen nutrition. As was predicted, for D. glomerata grown in high nitrogen, Jt was significantly higher in plants grown and measured at elevated pCO2 than for plants grown and measured at ambient pCO2. This was due to a significant increase in Jc exceeding any suppression of Jo. This increase in photochemistry at elevated pCO2 protected against photoinhibition at high light. For plants grown at low nitrogen, Jt was significantly lower in plants grown and measured at elevated pCO2 than for plants grown and measured at ambient pCO2. Elevated pCO2 again suppressed Jo; however growth in elevated pCO2 resulted in an acclimatory decrease in leaf Rubisco content that removed any stimulation of Jc. Consistent with decreased photochemistry, for leaves grown at low nitrogen, the recovery from a 3-h photoinhibitory treatment was slower at elevated pCO2.
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