Mesophyll conductance in two cultivars of wheat grown in glacial to super-elevated CO2 concentrations

Abstract

Mesophyll conductance (gm) is an important factor limiting photosynthesis. However, gm response to long-term growth in variable [CO2] is not well understood, particularly in crop plants. Here, we grew two cultivars of wheat (Halberd and Cranbrook), known to differ in gm under current environmental conditions, in four [CO2] treatments: glacial (206 μmol mol -1), pre-industrial (344 μmol mol -1), current ambient (489 μmol mol -1) and super-elevated (1085 μmol mol -1), and two water treatments (well-watered and moderate water limitation), to develop an evolutionary and future climate perspective on gm control of photosynthesis and water use efficiency (WUE). In the two wheat genotypes, gm increased with rising [CO2]from glacial to ambient [CO2], but declined at super-elevated [CO2]. The responses of gm to different growth [CO2]also depend on water stress; however, the specific mechanism of gm response to [CO2]remains unclear. Although gm and gm/gsc (mesophyll conductance/stomatal conductance) were strongly associated with the variability of photosynthetic rates (A) and WUE, we found that plants with higher gm may increase A without increasing gsc, which increased WUE. These results may be useful to inform plant breeding programs and cultivar selection for Australian wheat under future environmental conditions.

Moderate heat stress prevented the observed biomass and yield stimulation caused by elevated CO2 in two well-watered wheat cultivars

“…The temperature response of g m as well as the values recorded at 25 °C (0.25–0.31 mol m −2 s −1 bar −1 ) for Scout and Yitpi (Fig. 2 b) were similar to what has been reported for wheat (0.39) and other crop species (cotton = 0.73, soybean = 0.49 and rice = 0.67) (Von Caemmerer and Evans 2015 ; Jahan et al 2021 ). In contrast to our expectations that Scout would have higher WUE due to its selection based on a carbon isotope discrimination gene (Condon et al 2004 ), both wheat cultivars showed similar iWUE under most measurement and growth conditions in this study (Fig.…”

Heat Stress Prevented the Biomass and Yield Stimulation Caused by Elevated CO2 in Two Well-Watered Wheat Cultivars

“…Mesophyll conductance (g m ) increased up to 25°C then plateaued (Figure 1B). The temperature response of g m as well as the values recorded at 25°C (0.25-0.31 mol m -2 s -1 bar -1 ) for Scout and Yitpi (Figure 1B) were similar to what has been reported for wheat (0.39) and other crop species (cotton = 0.73, soybean = 0.49 and rice = 0.67) (Von Caemmerer and Evans 2015; Jahan et al 2021). Scout had slightly higher A sat , g s and g m than Yitpi at most leaf temperatures (Figures 1A-D).…”

Effects of leaf age during drought and recovery on photosynthesis, mesophyll conductance and leaf anatomy in wheat leaves

“…The value of g m was calculated from the difference between predicted discrimination assuming infinite mesophyll conductance (Δ i ) and measured discrimination (Δ obs ), as described by Jahan et al. (2021) using equations developed by Evans et al.…”

“…Photosynthetic rate ( A ) often has a strong positive correlation with mesophyll conductance ( g m , the diffusion of CO 2 from substomatal cavities to the carboxylation sites in the chloroplasts; Barbour et al., 2010 ; Giuliani et al., 2013 ; Jahan et al., 2014 ; Xiong et al., 2016 ; Ellsworth et al., 2018 ; Knauer et al., 2019 ; Gago et al., 2020 ; Jahan et al., 2021 ) and decreased g m is considered to be one of the main factors involved in early age-induced photosynthetic decline ( Niinemets et al., 2005 ; Flexas et al., 2007 ; Zhang et al., 2008 ). Conversely, Tosens et al.…”