| Research Abstract |
Vegetation of hygrophytes in wetland decreases the concentration of soil methane produced in the severely reduced conditions. The order of the decreasing power of the concentration of soil methande was erect bur marigold (E), sesbania (S) >reed (R) >rice (I) >Manchurian wild rice (M). The order of activity of methane production in rhizosphere soil was I,M,R>without hygrophytes>E,S.The activity of methane oxidation in rhizosphere soil was a little higher in the soil without hygrophtes and was hardly different among the soils overgrown with different kind of hygrophytes. In the model experiments (methane concentration in gas system was 70%, and that in liquid system was 1%), plants cultured previously in hydroponically under the low oxygen concentration developed lysigenous aerenchyma and emitted larger amounts of methane through their shoot than those precultured in aerobic conditions. The emission ability of methane through plants was considerably higher in gas system than in liquid sy
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stem, and the order was M> I,R,E> S.The order of release of atmospheric oxygen from roots was M> R> I> S> E.The order of oxidizing power of alpha-naphthylamine mediated both by peroxidase and hydrogen peroxide was E> R,S> M> I,and this power was higher in the tip portions of roots. The order of raising power of rhizosphere Eh was E,S> R> M,I.High concentration of hydrogen peroxide was detected in the apoplast of epidermis and cortex of E and S.High concentration of Fe^<2+> was detected in the solution of the severely reduced Soil. In vitro experiments, the dissolved methane was significantly decreased in the co-existing conditions of H_2O_2 and Fe^<2+>. Negation of the decrease in methane concentration by the addition of mannitol which is known as the scavenger of hydroxyl radical also suggests the direct scavenging of methane in the apoplast of roots with hydroxyl radical which is produced by Fenton reaction. Hygrophytes especially E and S considerably decreased the methane concentration in the solution added Fe^<2+>. In conclusion, E and S not only can suppress the production activity of methane in rhizosphere soil by their strong oxidizing power of roots but also possess the function to scavenge methane directly in their apoplast. These findings offer the novel and important data for the creation of new plants i.e., plants tolerant to the severely reduced conditions, and plants having highly suppressive ability of methane emission through plants. The antioxidative function of flavonoids and phenolic compounds in vegetables, fruits, and grasses was also elucidated. Less
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