Root O₂ consumption, CO₂ production and tissue concentration profiles in chickpea, as influenced by environmental...

Roots in flooded soils experience hypoxia, with the least O₂ in the vascular cylinder. Gradients in CO₂ across roots had not previously been measured. The respiratory quotient (RQ; CO₂ produced : O₂ consumed) is expected to increase as O₂ availability declines. A new CO₂ microsensor and an O₂ microsensor were used to measure profiles across roots of chickpea seedlings in aerated or hypoxic conditions. Simultaneous, nondestructive flux measurements of O₂ consumption, CO₂ production, and thus RQ, were taken for roots with declining O₂ . Radial profiling revealed severe hypoxia and c. 0.8 kPa CO₂ within the root vascular cylinder. The distance penetrated by O₂ into the roots was shorter at lower O₂ . The gradient in CO₂ was in the opposite direction to that of O₂ , across the roots and diffusive boundary layer. RQ increased as external O₂ was lowered. For chickpea roots in solution at air equilibrium, O₂ was very low and CO₂ was elevated within the vascular cylinder; the extent of the severely hypoxic core increased as external O₂ was reduced. The increased RQ in roots in response to declining external O₂ highlighted the shift from respiration to ethanolic fermentation as the severely hypoxic/anoxic core became a progressively greater proportion of the root tissues.