Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2010
Publication Date: 4/1/2011
Publication URL: http://naldc.nal.usda.gov/catalog/49258
Citation: Ort, D.R., Zhu, X., Melis, A. 2011. Optimizing antenna size to maximize photosynthetic efficiency. Plant Physiology. 155:79-85. Interpretive Summary: The United Nation's Food and Agricultural Organization posits that agricultural production will need to double within the next 50 years in order to meet agricultural demand and avoid food shortages and large increases in the cost of food. Since there is little additional land that can be sustainably recruited into cultivation the doubling of production will require a doubling of productivity on a land area basis. With many global climate change factors militating against increased productivity the challenge of doubling productivity is large, daunting and urgent. Only through improving photosynthetic efficiency of crop plants will it be possible to meet this challenge. Optimizing the amount of chlorophyll present in a crop canopy is among the most promising strategies to improve photosynthetic efficiency of crops in the near term yet no breeding has been directed at this goal. In this work we develop the theory on which chlorophyll optimized canopies can be designed.
Technical Abstract: The theoretical upper limit for the operational efficiency of plant photosynthesis has been estimated from a detailed stepwise analysis of the biophysical and biochemical subprocesses to be about 4.6% for C3 and 6.0% C4 plants. The highest short term efficiencies observed for plants in the field, assessed from maximum growth rates, are about 3.5% of C3 and 4.3% for C4 plants and these drop further to 2.4% and 3.4% when calculated over a full growing season. The primary reason why the highest observed photosynthetic efficiencies are 30% or more lower than theoretical efficiencies is light saturation of photosynthesis. Photosynthesis responds non-linearly to increases in insolation. For example, C3 leaf photosynthesis is saturated by ~25% of maximum full sunlight and light intercepted above this amount will lower photosynthetic efficiency in proportion to the excess light absorbed . In plant canopies this leads to a situation in which photosynthetic tissue directly exposed to bright sunlight is saturated and wastefully dissipates energy while photosynthesis in shaded leaves are light limited. Lowering the chlorophyll (Chl) content of photosynthetic tissue is a potentially robust strategy to improve light penetration into plant canopies. Here we discuss the theory and physiological factors that need to be considered in optimizing Chl content for improved photosynthetic efficiency and maximum carbon gain by crops.