Sensitivity of chickpea and faba bean to root‐zone hypoxia, elevated ethylene, and carbon dioxide.

During soil waterlogging, plants experience O2 deficits, elevated ethylene, and high CO2 in the root‐zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 μL L−1), CO2 (2–20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO2 reduced root growth of both species, but O2 deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO2 inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas‐filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O2 movement was more prominent in faba bean when in an O2‐free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O2, such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO2 partially inhibited root extension in both species, but low O2 in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O2 condition than faba bean. Roots in waterlogged soil can experience O2 deficits, elevated ethylene, and high CO2. Faba bean was more tolerant than chickpea, to growth in stagnant deoxygenated nutrient solution, as the gas‐filled porosity and internal O2 movement were greater in the roots of faba bean than in chickpea. Ethylene (2 μL L−1) and high CO2 (2–20% v/v) each reduced root growth of both species, and high CO2 inhibited root respiration. Thus, ethylene and high CO2 can partially inhibit root growth, but low O2 had the most damaging effect on the roots of these cool‐season grain legume species. [ABSTRACT FROM AUTHOR]