Submitted to: Current Opinion in Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2008
Publication Date: 4/1/2008
Citation: Zhu, X., Long, S.P., Ort, D.R. 2008. What is the maximum efficiency with which photosynthesis can convert solar energy into biomass? Current Opinion in Biotechnology. 19(2):153-159. Interpretive Summary: This work examines opportunities for further improvements in yield potential based on improved photosynthesis. It shows 1) that photosynthesis is the only remaining major trait available for further increases in yield potential on the scale of the past 50 years; 2) that increasing leaf photosynthesis will increase yield when other factors are held constant; 3) the theoretical limits to crop light use as a framework for identifying opportunities for improvement of photosynthesis; and 4) that there are specific options for improving leaf photosynthesis that would result in improved canopy light use efficiency and that some of these changes might be realized on a short time scale. This paper directly confronts the long-standing notion that crop photosynthetic performance is not directly coupled to yield and thus informs the crop breeding strategies as to highly significant target physiological traits.
Technical Abstract: Current photosynthesis is directly or indirectly the source of all of our food and fiber and is increasingly looked on as a potential source of renewable fuels. Increasing world population, improving economic status of portions of the developing world, and limited scope for recruitment of additional arable land, forecast that a doubling of productivity on a land area basis will be needed to meet agricultural demand before the end of this century. A starting point for evaluating the global potential to meet this goal is to critically evaluate the maximum efficiency of photosynthetic solar energy conversion that is possible; i.e., the upper limit of what theoretically could be achieved in managed ecosystems. Based on the current detailed understanding of the component mechanisms of plant photosynthesis our analyses show that, before accounting for mitochondrial respiration, the maximum efficiency possible for conversion of solar energy to biomass is 6.5% for C3 photosynthesis operating at 30C and today's level of atmospheric [CO2]. Whereas the upper limit of solar energy conversion efficiency of C4 photosynthesis is substantially higher at 8.5%, our analysis shows that this advantage over C3 will disappear later this century as atmospheric [CO2] nears 700 ppm.