Elevated CO2 alleviates the negative impact of heat stress on wheat physiology but not on grain yield.

Sachin G Chavan,Remko A Duursma,Oula Ghannoum,Michael Tausz,Robert Hancock

doi:10.1093/jxb/erz386

Abstract

Hot days are becoming hotter and more frequent, threatening wheat yields worldwide. Developing wheat varieties ready for future climates calls for improved understanding of how elevated CO2 (eCO2) and heat stress (HS) interactively impact wheat yields. We grew a modern, high-yielding wheat cultivar (Scout) at ambient CO2 (aCO2, 419 μl l -1) or eCO2 (654 μl l-1) in a glasshouse maintained at 22/15 °C (day/night). Half of the plants were exposed to HS (40/24 °C) for 5 d at anthesis. In non-HS plants, eCO2 enhanced (+36%) CO2 assimilation rates (Asat) measured at growth CO2 despite down-regulation of photosynthetic capacity. HS reduced Asat (-42%) in aCO2- but not in eCO2-grown plants because eCO2 protected photosynthesis by increasing ribulose bisphosphate regeneration capacity and reducing photochemical damage under HS. eCO2 stimulated biomass (+35%) of all plants and grain yield (+30%) of non-HS plants only. Plant biomass initially decreased following HS but recovered at maturity due to late tillering. HS equally reduced grain yield (-40%) in aCO2- and eCO2-grown plants due to grain abortion and reduced grain filling. While eCO2 mitigated the negative impacts of HS at anthesis on wheat photosynthesis and biomass, grain yield was reduced by HS in both CO2 treatments.

Highlights

Rising atmospheric CO2 concentration is the primary cause of increasing global mean surface temperatures as well as increased frequency, duration, and intensity of heat waves
At 13 weeks after planting (WAP), growth under elevated CO2 (eCO2) reduced assimilation rates (Asat) measured at common CO2 at both 25 °C (–12%, P=0.004) (Fig. 1a; Table 1; and Supplementary Table S1) and 35 °C (–13.3%, P=0.01) (Table 1; Supplementary Table S1).At 13 WAP, eCO2 enhanced Asat of non-heat stress (HS) plants measured at growth CO2, at both 25 °C (+25%, P=0.003) (Fig. 1a;Table 1; Supplementary Table S1) and 35 °C (+39%, P
Relative to 13 WAP, Asat decreased after 50% anthesis (17 WAP), but was not affected by eCO2 in non-HS plants measured at common CO2 and 25 °C or 35 °C (Fig. 1b, c; Table 1; Supplementary Table S1)

Summary

Introduction

Rising atmospheric CO2 concentration is the primary cause of increasing global mean surface temperatures as well as increased frequency, duration, and intensity of heat waves. Only a few studies have considered the interaction between eCO2 and warming in wheat (Rawson, 1992; Delgado et al, 1994; Morison and Lawlor, 1999; Jauregui et al, 2015; Cai et al, 2016), and less frequently included HS (Wang et al, 2008, 2011; Shanmugam et al, 2013; Fitzgerald et al, 2016). A few studies have considered the interactive effects of eCO2 and HS on wheat photosynthesis (Wang et al, 2008, 2011; Shanmugam et al, 2013; Macabuhay et al, 2018).These studies emphasize the need to determine the impacts of HS application at the vegetative and the important reproductive stage

Objectives

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Results

Conclusion