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Title: RESPONSES OF SOYBEAN TO OXYGEN DEFICIENCY AND ELEVATED ROOT-ZONE CARBON DIOXIDE CONCENTRATION

Author
item BORU, G - OHIO STATE UNIV.
item Vantoai, Tara
item ALVES, J - UNIV FED DE LAVRAS
item HUA, D - OHIO STATE UNIV.
item KNEE, M - OHIO STATE UNIV.

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2002
Publication Date: 1/23/2003
Citation: BORU, G., VANTOAI, T.T., ALVES, J., HUA, D., KNEE, M. RESPONSES OF SOYBEAN TO OXYGEN DEFICIENCY AND ELEVATED ROOT-ZONE CARBON DIOXIDE CONCENTRATION. ANNALS OF BOTANY. 2003. V. 99. P. 447-453.

Interpretive Summary: Root flooding diminishes the growth of crop plants such as soybean. Annual soybean yield loss to root flooding exceeds 10 percent. The cause has been widely attributed solely to a lack of oxygen in the root-zone. However, soybean was found to grow well and show no injury when grown in the laboratory with the roots submerged in water containing nutrients but without oxygen. An additional factor that may damage soybean in the field is the amount of carbon dioxide (CO2) gas in the soil. Laboratory experiments with soybean roots submerged in water containing nutrients and differening amounts of CO2 showed that soybean plants are very tolerant to excess water and the lack of oxygen, but are injured when CO2 concentration increases to that found in flooded soybean fields (30%). Rice, a flooding tolerant species, showed no injury at the same CO2 concentration. Our results suggest that the high susceptibility of soybean to soil flooding, compared to rice, is its greater sensitivity to CO2 in flooded soil. This information will be very useful to plant breeders and geneticists in developing new varieties of soybean that can tolerate some root flooding.

Technical Abstract: Root flooding is damaging to growth of crop plants such as soybean (Glycine max L.). These effects have been widely attributed solely to a lack of oxygen in the root-zone. However, soybean was found to tolerate the lack of oxygen and showed no injury after 4 weeks of growth in solutions without oxygen. An additional factor to the lack of oxygen that damages soybean in the field may be CO2 which attain levels of 50% (v/v) of the total dissolved gases. Accordingly, the effects of root-zone CO2 on oxygen-deficient soybean plant were investigated in hydroponic culture. We showed that soybean plants are very tolerant to excess water and anaerobiosis. The no oxygen (100% N2 gas) and low oxygen (non-aerated) treatments for 14 d had no effect on soybean survival or leaf greenness. But the plants became severely chlorotic and stunted when exposed to root-zone with no oxygen and CO2 concentrations similar to those in flooded field equilibrium concentrations (30%). When root-zone CO2 was increased to 50%, 25% of soybean plants died. Surviving plants showed severe symptoms of chlorosis, necrosis and root death. In contrast, rice (Oryza sativa L.) plants were not affected by the combination of no oxygen and elevated root-zone CO2. The 50% root-zone CO2 did not affect rice plant survival or its leaf color. Our results suggest that the high susceptibility of soybean to soil flooding, compared to rice, is an outcome of its greater sensitivity to CO2.