How Will the Two Major Midwest Crops Respond to Global Climate Change? Results From Ten Years of Investigation At Soyface.

The Soybean Free Air Concentration Enrichment (SoyFACE) facility is an open-air field "laboratory" for investigating the effects of elevated concentrations of CO2 and ozone, higher temperatures and altered soil water availability on field crops. For over a decade, experiments have examined the productivity, physiology and genetics of crop responses to atmospheric and climatic change in the field under replicated, fully open-air conditions. Rising atmospheric CO2 stimulated photosynthesis and yield in crops with C3 photosynthesis (soybean and cassava), but had no effect on C4 crops (maize and Miscanthus). However, any increase in background ozone concentration above ambient caused a linear decrease in soybean seed yield of ~ 0.5 bu/acre per ppb ozone. When elevation of CO2 and temperature were combined, the theoretically predicted synergy was not observed in terms of a greater stimulation of photosynthesis, biomass and yield compared to increased CO2 alone. Rather the effect of warming in addition to elevated CO2 was strongly dependent upon the background temperature. In a cooler than average growing season, warming did not alter the CO2 response, but in a warmer than average growing season, warming the canopy 3.5 °C caused a significant reduction in seed yield (-44%). The response of soybean to elevated CO2 and drought stress also varied from growing season to growing season, and elevated CO2 did not always compensate for the deleterious effects of drought on soybean seed yield. Again this questions the expectation that the direct effects of rising CO2 on C3 crops will ameliorate the impacts of drought. Overall these open-air investigations of the direct effects of atmospheric and climatic change on soybean and maize, the Midwest's two major crops, paint a pessimistic picture for future productivity. However, the experiments have also revealed significant variation within germplasm, suggesting that targeted breeding could lessen the impacts of climate change.