Responses to Root‐Zone CO2 Enrichment and Hypoxia of Wheat Genotypes Differing in Waterlogging Tolerance

Abstract

Knowledge of wheat (Triticum aestivum L.) responses to CO2 and O2 in the root environment could improve understanding of the mechanisms of waterlogging tolerance and thus help develop waterlogging tolerance wheat plants. This experiment was designed to investigate the responses to elevated CO2 and hypoxia of two wheat genotypes, Bayles and Savannah, which differ in waterlogging tolerance. Plants were grown in a growth chamber in nutrient solutions. Nutrient solutions were bubbled with ambient air (control), N2 containing 5 kPa O2 and ambient CO2 (hypoxia), N2 containing 10 kPa CO2 and ambient O2 (high CO2, ambient O2), and N2 containing 10 kPa CO2 and 5 kPa O2 (high CO2, low O2). Hypoxia alone had adverse effects on net photosynthesis (Pn), stomatal conductance (gs), water relations, chlorophyll (chl) content, and shoot and root growth. The effects were greater for waterlogging‐sensitive Bayles. When compared with the aerated control, the combination of elevated CO2 and hypoxia caused significant reductions in Pn, gs, leaf water potential, and leaf chl content for Bayles, and in shoot and root growth for both Bayles and Savannah. Photosynthetic rate and leaf chi content of Savannah were increased when roots of hypoxic plants were exposed to elevated CO2, but this was not true for Bayles. Root‐zone CO2 enrichment at ambient O2 had no significant effects on shoot growth, but reduced root growth in both genotypes. The results showed that CO2 enrichment under root hypoxia can alleviate some negative effects of hypoxia on Pn, leaf chi content, and shoot growth, the effect being larger for waterlogging tolerance Savannah.