Field-grown soybean shows genotypic variation in physiological and seed composition response to heat stress during seed development

Authors: Ortiz, Anna; DE SMET, IVE - North Carolina State University; SOZZANI, ROSANGELA - North Carolina State University; Locke, Anna

Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2021
Publication Date: 12/29/2021
Citation: Ortiz, A.C., De Smet, I., Sozzani, R., Locke, A.M. 2021. Field-grown soybean shows genotypic variation in physiological and seed composition response to heat stress during seed development. Environmental and Experimental Botany. https://doi.org/10.1016/j.envexpbot.2021.104768.
DOI: https://doi.org/10.1016/j.envexpbot.2021.104768

Interpretive Summary: Average temperatures are expected to increase by the end of the century, and heat waves are becoming more frequent. Higher temperatures can reduce soybean productivity, but little is known about variation in heat stress responses among soybean varieties. In this study, we measured photosynthetic and agronomic responses of six soybean genotypes to increased air temperatures during the seed fill period in the field. The heat treatment consistently increased nighttime respiration rates and reduced seed oil concentration across all six genotypes. The responses to heat varied among genotypes for midday photosynthesis, stomatal conductance, and seed protein concentration. Yield differences could not be statistically resolved. These results indicate variation for heat stress exists in soybean germplasm when grown in the field, and this variation should be further explored to improve soybean heat tolerance.

Technical Abstract: An average temperature increase between 2.6 and 4.8 °C, along with more frequent extreme temperatures, will challenge crop productivity by the end of the century. To investigate genotypic variation in soybean response to elevated temperature, six soybean (Glycine max) genotypes were subjected to elevated air temperature of +4.5 °C above ambient for 28 days in open-top field chambers. Gas exchange and chlorophyll fluorescence were measured before and during heating, and yield and seed composition were evaluated at maturity. Elevated air temperature increased nighttime respiration increased the maximum velocity of carboxylation by Rubisco, impacted seed protein concentration, and reduced seed oil concentration across genotypes. The genotypes in this study varied in temperature responses for photosynthetic CO2 assimilation, stomatal conductance, photosystem II operating efficiency, quantum efficiency of CO2 assimilation, and seed protein concentration at maturity. These diverse responses among genotypes to elevated temperature during seed development in the field reveal the potential for soybean heat tolerance to be improved through breeding and underlines the importance of identifying efficient selection strategies for stress-tolerant crops.