Reductions in leaf area index, pod production, seed size, and harvest index drive yield loss to high temperatures in soybean

Authors: BURROUGHS, CHARLES - University Of Illinois; Montes, Christopher; MOLLAR, CHRISTOPHER - University Of Illinois; MITCHELL, NOAH - University Of Illinois; MICHAEL, ANNMARIE - Washington University; PENG, BIN - University Of Illinois; KIMM, HYUNGSUK - University Of Illinois; PEDERSON, TAYLOR - University Of Illinois; LIPKA, ALEXANDER - University Of Illinois; Bernacchi, Carl; GUAN, KAIYU - University Of Illinois; Ainsworth, Elizabeth - Lisa

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2022
Publication Date: 3/13/2023
Citation: Burroughs, C.H., Montes, C.M., Mollar, C.A., Mitchell, N.G., Michael, A., Peng, B., Kimm, H., Pederson, T.L., Lipka, A.E., Bernacchi, C.J., Guan, K., Ainsworth, E.A. 2023. Reductions in leaf area index, pod production, seed size, and harvest index drive yield loss to high temperatures in soybean. Journal of Experimental Botany. 74(5):1629-1641. https://doi.org/10.1093/jxb/erac503.
DOI: https://doi.org/10.1093/jxb/erac503

Interpretive Summary: Soybean yields are expected to continue to rise as genetics and technology improve further; however, climate conditions detrimental to crop productivity could prevent these gains from being fully realized. Studies of historic yield and climate data indicate that increasing growing season temperatures have negatively affected yields. However, the physiological mechanisms that lead to yield loss are not fully known. This study used in-field infrared heaters to test the response of commercial soybean to four different temperature treatments. Soybean yield decreased with increasing temperature and the decline in yield was driven by changes in canopy size, pod number per node, seed size and harvest index, with leaf-level photosynthesis and respiration not having as much influence. These field experiments reinforce conclusions drawn from historical data that higher growing season temperatures result in lower soybean yields, even in temperate environments.

Technical Abstract: Improvements in genetics, technology, and agricultural intensification have increased soybean yields; however, adverse climate conditions may prevent these gains from being fully realized in the future. Higher growing season temperatures reduce soybean yields in key production regions including the US Midwest, and better understanding of the developmental and physiological mechanisms that constrain soybean yield under high temperature conditions is needed. This study tested the response of two soybean cultivars to four elevated temperature treatments (+1.7, +2.6, +3.6, and +4.8 °C) in the field over three growing seasons and identified threshold temperatures for response and linear versus non-linear trait responses to temperature. Yield declined non-linearly to temperature, with decreases apparent when canopy temperature exceeded 20.9 °C for the locally adapted cultivar and 22.7°C for a cultivar adapted to more southern locations. While stem node number increased with increasing temperature, leaf area index decreased substantially. Pod production, seed size, and harvest index significantly decreased with increasing temperature. The seasonal average temperature of even the mildest treatment exceeded the threshold temperatures for yield loss, emphasizing the importance of improving temperature tolerance in soybean germplasm with intensifying climate change.