Submitted to: Annual Reviews of Plant Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2010
Publication Date: 7/1/2010
Citation: Zhu, X., Long, S.P., Ort, D.R. 2010. Improving Photosynthetic Efficiency for Greater Yield. Annual Reviews of Plant Biology. 61:235-261. Interpretive Summary: In order to meet agricultural demand, a doubling of crop productivity will be required by the end of this century and this will have to be achieved in the face of face of climate change. Those elements of crop physiology and agronomy that drove the previous doubling of productivity during the Green Revolution have been fully exploited in the major crop species. Photosynthetic solar energy conversion efficiency is the only component of crop yield potential that has sufficient capacity for improvement to drive a doubling of productivity. Several of the most accessible targets for improving photosynthetic solar energy conversion efficiency are found in adapting crop plants to current and future elements of global change. These model predications and proof of concept experiments point to clear directions that can be taken to meet increasing agriculture demand.
Technical Abstract: Increasing the yield potential of the major food grain crops has contributed very significantly to a rising global supply of grain over the past 50 years, which has until recently more than kept pace with rising global demand. Yield potential is the product of the solar radiation available at a given location and the efficiencies to radiation interception, conversion of intercepted radiation into biomass, and partitioning of that biomass energy into grain. This analysis shows that for modern cultivars efficiency of interception and partitioning are close to their theoretical maximum. This leaves only conversion efficiency, which we show to be far below its theoretical maximum, for future improvement. Therefore the need to improve crop photosynthesis is not a distant challenge but is already upon us. Improved photosynthetic efficiency has played only a minor roll in the remarkable increases in productivity achieved in last half century. Here we examine inefficiencies in photosynthetic energy transduction in crops from interception to carbohydrate synthesis, and how classical breeding, systems biology and synthetic biology is providing new opportunities to develop more productive germplasm. Specific opportunities are explained. Near-term include improving the display of leaves in crop canopies to avoid light saturation of individual leaves and a photorespiratory bypass which has already improved the productivity of model species. Longer-term opportunities include engineering carboxylases into plants better adapted to to-day's elevated CO2 concentration and the use of evolutionary algorithms to guide molecular optimization of resource investment between components of the photosynthetic apparatus, to maximize carbon gain without increasing crop inputs. Collectively, these changes could more than double the yield potential of our major grain crops.