Yield response of field-grown soybean exposed to heat waves under current and elevated [CO2]

Authors: THOMEY, MICHELL - University Of Illinois; SLATTERY, REBECCA - Former ARS Employee; KOEHLER, IRIS - University Of Illinois; Bernacchi, Carl; ORT, DONALD - University Of Illinois

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2019
Publication Date: 8/14/2019
Citation: Thomey, M.L., Slattery, R.A., Koehler, I.H., Bernacchi, C.J., Ort, D.R. 2019. Yield response of field-grown soybean exposed to heat waves under current and elevated [CO2]. Global Change Biology. 25(12):4352-4368.

Interpretive Summary: Heatwaves are defined as periods of excessively warm temperatures lasting a relatively short duration (3-10 day) with temperatures well above long-term averages. Our previous research shows that heatwaves have a negligible impact on crop yields when the heatwave occurs early in the growing season before crop reproductive development begins. However, after reproductive development begins heatwaves were shown to cause crop yields to decline. Because rising atmospheric carbon dioxide, a direct consequence of human activities, is causing warming global temperatures the frequency of heatwaves are likely to increase. However, rising carbon dioxide also leads to higher yields. Thus, this study investigated whether high carbon dioxide would offset some or all of the damaging impacts of heatwaves on crop yields. The results show that elevated carbon dioxide increases yields but does not protect against the damaging impact of heatwaves. This research fills a critical need to understand the role climate change on crop yields in the future.

Technical Abstract: Elevated atmospheric CO2 concentration ([CO2]) generally enhances C3 plant productivity, whereas acute heat stress, which occurs during heat waves, generally elicits the opposite response. However, little is known about the interaction of these two variables, especially during key reproductive phases in important temperate food crops, such as soybean (Glycine max). Here, we grew soybean under elevated [CO2] and imposed high (+9°C) and low (+5°C) intensity heat waves during key temperature-sensitive reproductive stages (R1, flowering; R5, pod filling) to determine how future levels of [CO2] will interact with heat waves to influence soybean yield. High-intensity heat waves, which resulted in canopy temperatures that exceeded optimal growth temperatures for soybean, reduced yield compared to ambient conditions even under elevated [CO2]. This was largely due to heat stress on reproductive processes, especially during R5. Low intensity heat waves did not affect yields when applied during R1 but increased yields when applied during R5 likely due to relatively lower canopy temperatures, higher soil moisture, and faster recovery from heat stress, which uncoupled the negative effects of heating on cellular- and leaf-level processes from plant-level carbon assimilation. Modeling soybean yields based on carbon assimilation alone underestimated yield loss with high intensity heat waves and overestimated yield loss with low intensity heat waves, thus supporting the influence of direct heat stress on reproductive processes in determining yield. These results have implications for rain-fed cropping systems and point towards a climatic tipping point for soybean yield when future heat waves exceed optimum temperature.