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

Anna C Ortiz,Rosangela Sozzani,Ive De Smet,Anna M Locke

doi:10.1016/j.envexpbot.2021.104768

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 as well as seed composition were evaluated at maturity. Results show that long-term 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 CO 2 assimilation, stomatal conductance, photosystem II operating efficiency, quantum efficiency of CO 2 assimilation, and seed protein concentration at maturity. These diverse responses among genotypes to elevated air 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. • Six soybean genotypes were exposed to elevated air temperature in the field. • Several physiological responses to elevated temperature varied among genotypes. • Elevated temperature increased nighttime respiration across genotypes. • Elevated temperature reduced seed oil concentration across genotypes. • Seed protein concentration response to temperature varied among genotypes.

Highlights

As a part of climate change, atmospheric temperatures are projected to increase worldwide at an average rate of 0.3 ◦C per decade, with a likely + 1.5 ◦C rise in the 20 years, corresponding to projections under the most severe climate models (Collins et al, 2013; Lee et al, 2021)
Relative humidity in elevated temperature (ET) plots was 18% lower than ambient temperatures (AT) (66.2% and 85.3%, respectively) during the 4-week heating period
The average solar noon tem peratures in ET plots (22 ◦C) during this period were lower than the warmest AT temperatures recoded during the treatment period (23 ◦C)

Summary

Introduction

As a part of climate change, atmospheric temperatures are projected to increase worldwide at an average rate of 0.3 ◦C per decade, with a likely + 1.5 ◦C rise in the 20 years, corresponding to projections under the most severe climate models (Collins et al, 2013; Lee et al, 2021). In the United States, heat waves surpassing the optimum tem peratures for crops are expected to increase in frequency, in regions with high agricultural productivity (Gornall et al, 2010; Hat field et al, 2011; Herring et al, 2016; Liang et al, 2017). The highest of the projected global mean temperature scenarios for the end of the century, RCP8.5, predicts an average temperature increase of 2.6–4.8 ◦C above current conditions (Collins et al, 2013). Modeling predicts that a temperature change of even 1.8–2.4 ◦C will stall soybean yield gains by mid-century (Iizumi et al, 2017). Improving soybean heat tolerance is vital for food security and identifying and harnessing genetic variation for heat stress response could play an important role in crop improvement

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Results

Conclusion