Global Climate Change

Carbon Dioxide and Temperature Interactions

Carbon dioxide concentration is increasing and is predicted to cause global warming which will have a significant impact on crop production. There are few data to develop mechanistic crop models to use for studies on global climatic change on crop production. We therefore conducted several controlled-environment studies with carbon dioxide and temperature as treatments on cotton. The objectives were (1) to study the direct and interactive effects of temperature and carbon dioxide on cotton photosynthesis, transpiration, water use efficiency, fruit initiation and abscission, growth and developmental rates, (2) to study the direct and interactive effects of temperature and carbon dioxide on main stem and branch expansion rates, node initiation, fruiting, leaf initiation and expansion rates, and (3) to develop a database for a comprehensive cotton simulation model that can be used for predicting the effects of future climate change on cotton at the physiological process level. The data were analyzed and used in the development of the Sigma+ cotton simulation model. Several manuscripts and algorithms for developing and testing the crops models were developed using this database and the database was made available to modelers worldwide.

Regional Estimates of Crop Development and Yields  Under Global Change

A methodology was developed to use mechanistic crop simulators in regional estimates of the effect of atmospheric carbon dioxide enrichment and climate change. This methodology includes an upscaling technique to generate distributions of soil parameters for soil associations, a downscaling technique to use monthly weather projections of the general circulation models to generate equiprobable daily weather sequences, and various data handling and management techniques. The database of the National Center of Atmospheric Research was used to obtain input data from the global circulation models developed by the Goddard Institute for Space Studies, Geophysical Fluid Dynamics Laboratory, and United Kingdom Meteorological office. The methodology was validated using county and state level data on soybean yields in Iowa. We then estimated climate change effects in Iowa soybean yields and found that changes in atmospheric carbon dioxide were primary determinants of the yield responses, and that the variability of the simulated yields among Crop Reporting Districts increased for all scenarios. We also estimated climate change effects on carbon partitioning between shoots and roots in cotton crops over the Cotton Belt and in soybeans crops in Southern US, and found that the proportion of roots in total dry biomass did not change significantly in soybean crops but significantly increased in cotton crops, with the increase being larger in the west.

Carbon Dioxide and Ozone Interactions

Concomitant increases of atmospheric carbon dioxide and ozone have been observed during the past century and are predicted to continue. The effects of carbon dioxide enrichment and chronic ozone stress on corn, soybeans, and wheat grown in large open-top chambers were studied. Carbon dioxide enrichment had a physiologically beneficial effect on wheat (C3 crop) but not on corn (C4 crop). Increases in ozone concentrations reduced dry matter and grain production of all crops. It is likely that stress induced by exposure to ozone in all crops will be reduced by increased atmospheric carbon dioxide concentrations; however maximal benefits in crop production in wheat in response to carbon dioxide enrichment will not materialize with concomitant increases in atmospheric ozone concentration.