August 30, 2013
The Green Revolution of the 1960s may have been thrown into reverse by climbing concentrations of carbon dioxide in the atmosphere, German scientists have found. Carbon dioxide is a core component of plant growth, leading to forecasts that increased CO2 concentrations could boost some crop yields. But for dwarf crop varieties – one of the scientific breakthroughs of the Green Revolution – the opposite might be the case, according to researchers at the University of Potsdam. They looked at the dwarf rice variety IR8, which was a sensation when it was introduced in the 1960s because its short, strong stalks allowed it to support much bigger grain heads. Because it had less vertical vegetative growth that traditional varieties, IR8 also needed less water and nutrient. But while genetically, IR8 is unchanged, the variety’s yields have declined 15 per cent since its introduction, and it has almost disappeared from the market. What has changed are CO2 concentrations in the atmosphere. They are about 25 per cent higher than when IR8 was introduced. A characteristic of dwarf varieties is that they lack the enzyme needed to produce the plant growth hormone gibberellic acid. This ensures the plant invests less effort in growing vegetation, and more in the seed head. But the Potsdam team found that higher levels of CO2 unblocks the plant’s ability to form gibberellic acid. As more of the hormone is used in the plant’s growth cycle, it has reverted towards its pre-dwarf form and yield. Along with rice, dwarfing also revolutionised wheat yields. Lead researcher, Jos Schippers, said: “Breeders now face the challenge of developing new plants that can continue to provide good yields under the altered climatic conditions”.