Submitted to: Global Change Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2004
Publication Date: 1/3/2005
Citation: Morgan, P.B., Bollero, G.A., Nelson, R.L., Dohleman, F.G., Long, S.P. 2005. Smaller than predicted increase in above ground net primary production and yield of field-grown soybean under fully open-air [CO2] elevation. Global Change Biology. 11:1-10. Interpretive Summary: The concentration of carbon dioxide concentration (CO2) in the atmosphere has been steadily rising for more than a century and by 2050 The Intergovernmental Panel on Climate Change predicts it will be 550 ppm, which is 50% higher than it was in 1900. Increases in CO2 generally increase plant growth but previous studies with soybeans have only been conducted in fully or partially enclosed chambers. Technology now exists to increase the CO2 concentration in totally open field plots. Reported yields for the world's two major grain crops, wheat and rice, were substantially lower in these types of experiments than predicted from similar elevated CO2 concentration experiments within chambers. Our objective was to measure soybean yield under field conditions with CO2 concentrations that are expected to occur in 50 years. In our research elevated CO2 concentration increased total above-ground dry matter by 18% but seed yield only increased 15%. These responses were consistent across three growing seasons, but they are less than projected from previous chamber experiments. As in previous studies, we found that increasing CO2 concentration increased vegetative growth more than seed yield. Crop maturation was delayed and not accelerated, as previously reported. These results suggest that chamber studies may have over-estimated the stimulatory effect of rising CO2 concentration. These results will be of interest to those predicting future food production, and breeders, geneticists and other scientists who are working to develop soybean varieties that can more effectively exploit the increased CO2 concentration of the future.
Technical Abstract: The Intergovernmental Panel on Climate Change projects that carbon dioxide ([CO2]) will reach 550 p.p.m. by 2050. Numerous assessments of plant response to elevated CO2 have been conducted in chambers and enclosures, with only a few studies reporting responses in fully open-air, field conditions, which typically report smaller relative stimulation due to elevated CO2. Reported yields for the world's two major grain crops, wheat and rice, are substantially lower in FACE than predicted from similar elevated CO2 experiments within chambers. This has major implications for forecasting future global food supply. Globally, the leguminous-crop soybean (Glycine max) is planted on more land than any other dicotyledonous crop. Previous studies have shown that total dry mass production increased on average 37% in response to a doubling in CO2, but harvestable yield is increased only 24%. Is this representative of plant responses under fully open-air field conditions? The effects of elevation of CO2 to 550 p.p.m. on total production, partitioning and yield of soybean over three years are reported. This is the first FACE study of soybean and the first on crops in the Midwest of North America, one of the major food production regions of the globe. Elevated CO2 increased above-ground net primary production (17-18%) and yield (15%). Although both responses were consistent across three growing seasons and two cultivars (cv. Pana and Pioneer 93B15), they are less than projected from previous chamber experiments. As in previous studies, partitioning to seed dry mass decreased, but, in contrast, net production during vegetative growth did not increase and crop maturation was delayed and not accelerated, as previously reported. These results suggest that chamber studies may have over-estimated the stimulatory effect of rising CO2, with important implications global food supply forecasts.