Roots in waterlogged soils experience low O2 and often high CO2.<br/>Comparative responses of waterlogging-sensitive chickpea and<br/>-tolerant faba bean to high root-zone CO2 concentrations were studied<br/>in hydroponics. Plants were raised in aerated nutrient solution for 13<br/>days and then continued with aeration without additional CO2 or with<br/>2, 4, and 8% CO2 for 10 days. Some plants were also transferred to<br/>deoxygenated stagnant 0.1% agar nutrient solution. After 10 days of<br/>treatments some plants were shifted back to aerated solution to assess<br/>recovery for 7 days. Both genotypes showed sensitivity to CO2. Primary<br/>root growth, lateral root elongation and relative growth rate of roots<br/>all decreased progressively as the CO2 concentration was increased.<br/>In both genotypes, primary root porosity was only increased when in<br/>stagnant conditions and not when under high CO2 in aerated solution.<br/>There was a significant reduction in root respiration at 8% CO2 in both<br/>genotypes (not tested at the lower CO2 concentrations); respiration was<br/>in chickpea 61% of control and in faba bean 72% of control. In both<br/>genotypes there was an increase in root sugars at 8% CO2, so substrate<br/>was presumably not limiting respiration. Upon recovery, both genotypes<br/>showed only partial and delayed recovery of root growth from both high<br/>CO2 and from the stagnant treatment. This study on these two grain<br/>legumes adds to data in the literature on soybean, and shows that<br/>even if roots can access some O2, the high CO2 accumulation under<br/>waterlogging might also contribute to growth reductions.
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