METHANE EMISSIONS AND GROWTH OF SPARTINA PATENS IN RESPONSE TO SOIL REDOX INTENSITY

Laboratory experiments were conducted to determine the influence of soil redox intensity (Eh) on the growth, root porosity (POR), radial O-2 loss, and CH4 production, oxidation, and emission in Spartina patens (Aiton) Muhlenb. (salt meadow cordgrass). Plants were grown for 50 d in a Mississippi alluvial soil (silty-clay loam, Typic Fluvaquent) under controlled Ph values of 200, -200, and -300 mV. Plant growth decreased with increase in Eh intensity. Root dry weights decreased by 37% and shoot dry weights by 25% between the soil redox intensity treatments of 200 and -300 mV. Root air space formation was enhanced by a decrease in Ph up to about 30 d when further development appeared to cease and levelled off in all the redox treatments. Methane production was generally enhanced by the intensity of reduction. Plant-mediated emissions were commensurate with production levels but were influenced by plant related factors, especially FOR. No differences (P < 0.05) existed between emissions in light and in the dark, which suggests a lack of stomatal influence on CH4 emissions from S. patens. Plant-mediated CH4 oxidation was higher at -200 mV than at -300 mV by a factor of 16%. Results of this study demonstrate how soil redox intensity initiates physiological changes in S. patens, which in turn modulates the gas transport in the plant. Although the experimental conditions do not represent the natural environment, the results provide a theoretical understanding of the influence of soil redox intensity on the growth, CH4 production, and gas exchange in S. patens.