Any increases in soybean crop yield from rising carbon dioxide (CO 2 ) levels may be eliminated by the i ntensified droughts that are expected to accompany the increased CO2 concentration, reports a paper published online this week in Nature Plants.
Previous studies have suggested that rising concentrations of atmospheric CO 2 througho ut this century will stimulate the yield of soybean crops (an effect called CO2 fertilization), counteracting the negative impacts of greater drought on futu re food production. In this study, Andrew Leakey and colleagues grew a commercial variety of soybean over eight consecutive years at a facility in Illinois, in the Midwestern United States. They maintained elevated levels of CO2 by releasing the gas from pipes surrounding the experimental plots, and created drought-like conditions by catching rainfall with retractable awnings deployed over the plants.
The authors found that soybean yields increased by up to 22% as a result of CO2 fertilization in years with adequate rainfall, but in dry years this effect became negligible. They attribute this to an increased sensitivity of stomata - the tiny pores through which gases and water enter and exit leaves - to drought signals and reduced nitrogen storage in drier soils, and suggest that such effects may be even more important in parts of the world that are drier than the American Midwest.
In an accompanying News & Views article, Colin Osborne writes: “The major outcome of this new work is that future drought events may threaten the yield benefits of rising CO2 for one of the world’s most important crops in a region accounting for more than 25% of the global soybean harvest.”