JXB Advance Access originally published online on May 7, 2004
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Journal of Experimental Botany, Vol. 55, No. 400, pp. 1167-1175, May 1, 2004
© 2004 Oxford University Press
Limitations to Photosynthetic Performance |
The slow reversibility of photosystem II thermal energy dissipation on transfer from high to low light may cause large losses in carbon gain by crop canopies: a theoretical analysis
Received 2 December 2003; Accepted 2 March 2004
1 Departments of Plant Biology and Crop Sciences, University of Illinois, 190 Plant and Animal Biotechnology Laboratories, 1201 W Gregory Drive, University of Illinois, Urbana, IL 61801-3838, USA
2 USDA-ARS, University of Illinois, 190 Earl R. Madigan Laboratories, 1201 W Gregory Drive, University of Illinois, Urbana, IL 61801-3838, USA
* Present address: Center for Bioinformatics and Computational Biology, NIGMS/National Institute of Health, 45 Center Drive, Bethesda, MD 20892-6200, USA. To whom correspondence should be addressed at the Department of Plant Biology. Fax: +1 217 244 7563. E-mail: stevel{at}life.uiuc.edu
Regulated thermal dissipation of absorbed light energy within the photosystem II antenna system helps protect photosystem II from damage in excess light. This reversible photoprotective process decreases the maximum quantum yield of photosystem II (Fv/Fm) and CO2 assimilation (
CO2), and decreases the convexity of the non-rectangular hyperbola describing the response of leaf CO2 assimilation to photon flux (
). At high light, a decrease in CO2 has minimal impact on carbon gain, while high thermal energy dissipation protects PSII against oxidative damage. Light in leaf canopies in the field is continually fluctuating and a finite period of time is required for recovery of CO2 and when light drops below excess levels. Low CO2 and can limit the rate of photosynthetic carbon assimilation on transfer to low light, an effect prolonged by low temperature. What is the cost of this delayed reversal of thermal energy dissipation and CO2 recovery to potential CO2 uptake by a canopy in the field? To address this question a reverse ray-tracing algorithm for predicting the light dynamics of 120 randomly selected individual points in a model canopy was used to describe the discontinuity and heterogeneity of light flux within the canopy. Because photoprotection is at the level of the cell, not the leaf, light was simulated for small points of 104 µm rather than as an average for a leaf. The predicted light dynamics were combined with empirical equations simulating the dynamics of the light-dependent decrease and recovery of CO2 and and their effects on the integrated daily canopy carbon uptake (A'c). The simulation was for a model canopy of leaf area index 3 with random inclination and orientation of foliage, on a clear sky day (latitude 44° N, 120th day of the year). The delay in recovery of photoprotection was predicted to decrease A'c by 17% at 30 °C and 32% at 10 °C for a chilling-susceptible species, and by 12.8% at 30 °C and 24% at 10 °C for a chilling-tolerant species. These predictions suggest that the selection, or engineering, of genotypes capable of more rapid recovery from the photoprotected state would substantially increase carbon uptake by crop canopies in the field.
Key words: Leaf canopies, photoprotection, photosynthesis, reverse ray-tracing, yield loss.
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