Mesophyll CO₂ conductance and leakiness are not responsive to short‐ and long‐term soil water limitations in the C₄ plant Sorghum bicolor

Abstract

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A cross-scale analysis to understand and quantify effects of photosynthetic enhancement on crop growth and yield

“…Key physiological parameters are the maximum rate of Rubisco carboxylation ( V cmax ), maximum rate of PEP carboxylation ( V pmax ), and maximum rate of electron transport at infinite light intensity ( J max ). The baseline values of V cmax25 and J max25 for wheat (the subscripted number denotes value at the standard 25°C), and V cmax25 , V pmax25 and J max25 for sorghum were set to those observed previously (Silva-Pérez et al ., 2017, Sonawane & Cousins, 2020, Sonawane et al ., 2017). The value of J max25 along with α PSII and θ used in Eqn S4 gave a potential whole-chain linear electron transport rate ( J ) of 232 μmol m −2 s −1 at photosynthetic photon flux density (PPFD) of 1800 μmol m −2 s −1 and 25°C, comparable to that inferred from C 3 wheat data (Silva-Pérez et al ., 2017).…”

Differences in leaf anatomy determines temperature response of leaf hydraulic and mesophyll CO2 conductance in phylogenetically related C4 and C3 grass species

“…These measurements were performed at leaf temperatures of 15, 20, 25, 30, 35 and 40°C on a youngest fully expanded leaf from four plants placed in an LI‐6400XT leaf chamber. More details on leaf measurements conditions and the calculations for mesophyll conductance to CO 2 using 13 C in C 3 and 18 O in the C 4 are given in Sonawane & Cousins (2019, 2020), Serrano‐Romero & Cousins (2020), and Supporting Information Methods S1 and references therein. A portion of the leaf used in gas exchange was collected for enzyme assay, microscopy studies and the measurements of specific leaf area.…”

The carbon isotopic signature of C4 crops and its applicability in breeding for climate resilience

“…Consistent with theory, Twohey et al ( 2019 ) found a negative correlation between leaf δ 13 C and WUE as well as positive association of δ 13 C and transpiration over three different watering regimes in an experiment including four maize RILs. Decreases of δ 13 C under water deficit, when stomatal closure decreases C i /C a and increases WUE, have further been observed in several C 4 species, including Setaria (Ellsworth et al 2017 ), pearl millet (Brück et al 2000 ), maize (Dercon et al 2006 ), Australian C 4 grasses (Ghannoum et al 2002 ) and sorghum (Sonawane and Cousins 2020 ; Williams et al 2001 ). These results indicate that changes in C i /C a are also reflected in δ 13 C of C 4 species.…”

“…3 , Farquhar 1983 ). Henderson et al ( 1992 ) demonstrated that leakiness is relatively stable over a range of temperatures, CO 2 concentrations, and light intensities and in a recent study on sorghum no changes in leakiness were found in response to water deficit (Sonawane and Cousins 2020 ). Contrastingly, a significant response of leakiness to a high vapor pressure deficit has been observed for the C 4 grass Cleistogenes squarrosa by Gong et al ( 2017 ).…”

“…In summary, compared to C 3 plants a weaker correlation between Δ 13 C and WUE can be expected in C 4 plants. If bundle sheath leakiness is relatively constant, as suggested by experimental values for sorghum ( Sorghum bicolor ) and Amaranthus edulis (Henderson et al 1992 , 1998 ; Sonawane and Cousins 2020 ), it should be possible to use Δ 13 C as a proxy trait in breeding for developing more water use efficient C 4 crops.…”