Responses to root-zone CO2 enrichment and hypoxia of wheat genotypes differing in waterlogging tolerance

Knowledge of wheat (Triticum aestivum L.) responses to CO2 and O-2 in the root environment could improve understanding of the mechanisms of waterlogging tolerance and thus help develop waterlogging-tolerant 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), N-2 containing 5 kPa O-2 and ambient CO2 (hypoxia), N-2 containing 10 kPa CO2 and ambient O-2 (high CO2, ambient O-2), and N-2 containing 10 kPa CO2 and 5 kPa O-2 (high CO2, low O-2). Hypoxia alone had adverse effects on net photosynthesis (P-n), stomatal conductance (g(s)), water relations, leaf chlorophyll (chi) 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 P-n, g(s), leaf water potential, and leaf chi 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 O-2 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 P-n, leaf chl content, and shoot growth, the effect being larger for waterlogging-tolerant Savannah.