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Abstract
The cultivation of several hydrophytes, i.e., rice, barnyardgrass, early water-grass, reed, and Manchurian wild rice, led to the decrease of the methane concentration in soils along with plant growth. After the removal of the plant tops below the water surface the methane concentration in soils markedly increased compared with that in the non-cultivated soils. The decrease of the methane concentration in soil was considerable at higher planting densities. The behavior of the concentration of nitrogen gas in soils was opposite to that of methane as the cultivation of hygrophytes led to the decrease of the methane concentration in soils and increase of the nitrogen gas concentration in soils. Species differences in the ability to decrease the methane concentration in soils were revealed among hygrophytes in the following order: reed > early watergrass > barnyardgrass > rice. Methane concentration in the reed stems paralleled that in soils.
Hygrophytes developed lysigenous intercellular spaces or an aerenchyma throughout the whole plant.
Soil Eh values also increased with the decrease of the methane concentration in the rhizosphere soils.
These results suggest that hygrophytes decrease the methane concentration and increase the nitrogen gas concentration in rhizosphere soils through gas exchange between the atmosphere and soil.