Differences in CH₄ oxidation and pathways of production between rice cultivars deduced from measurements of CH₄ flux and δ¹³C of CH₄ and CO₂

Abstract

Abstract. We report measurements of CH4 flux and fil 3C and fid values of emitted CH4 and sediment CH4 and CO2 during the 1995 rice growing season in Beaumont, Texas. Four rice plant cultivars, Lemont, Mars, Cypress, and Della, and an unplanted plot were studied to provide possible explanations for the differences in CH4 emissions between cultivars. Using the measured isotope values, along with data of CH4 and CO2 concentrations and other ecosystem data, we determined differences between cultivars in the processes of oxidation and production throughout the growing season. For instance, rhizospheric CH4 oxidation increased as the season progressed in both Mars and Lemont cultivars. Late in the season, however, 71_+10% of CH4 produced in the Mars plot was oxidized compared to only 39_+10% in the Lemont plot. The contribution of acetate fermentation to methanogenesis at specific times during the season was calculated using measured isotopic values and assuming identical isotopic fractionation factors in methanogenic pathways for the cultivars. In these calculations a range of values for the contribution to CH4 production from acetate fermentation and CO2 reduction with H2 was estimated by considering different fractionation factors for the methanogenic CO2 reduction pathway and the possibility of a 10% contribution to CH4 production from acetate produced by homoacetogenesis. In general, a steady increase in the CH4 portion produced by acetate fermentation was noted in the Lemont cultivar, while an increase followed by a decrease near the end of the season was observed for the Mars cultivar.

Pathway of CH<sub>4</sub> production, fraction of CH<sub>4</sub> oxidized, and <sup>13</sup>C isotope fractionation in a straw-incorporated rice field

“…Therefore, δ 13 CH 4 (acetate) = −43 ‰ and −37 ‰ was assumed in this study, mainly because the δ 13 C-value of soil organic carbon (−27.4 ‰) is close to what Krüger et al (2002) reported (−26.7 ‰). The δ 13 CH 4 (acetate) ranging from −43 ‰ to −37 ‰ is also in good agreement with those used earlier (Sugimoto and Wada, 1993;Tyler et al, 1997;Bilek et al, 1999;Conrad et al, 2002). To our knowledge, measurements of fractionation factor ε acetate/CH 4 during acetoclastic methanogenesis are still scarce (Conrad, 2005).…”

“…Fortunately, it has been validated in the other experiments we conducted (Zhang et al, 2011b. It is much higher than those in earlier reports (Sugimoto and Wada, 1993;Tyler et al, 1997;Bilek et al, 1999;Chidthaisong et al, 2002;Krüger et al, 2002;Valentine et al, 2004), indicating fractionation factor α CO 2 /CH 4 should not be assumed to be the same for different experiments and situations. Such differences may result from variation in the community structure of methanogens with the soil and the duration and condition of incubation (Chin et al, 1999;Lueders and Friedrich, 2000;Chidthaisong et al, 2002;Conrad et al, 2002;Krüger et al, 2002;Ramakrishnan et al, 2002).…”

“…In the study of CH 4 production and oxidation processes in the rice ecosystem, the stable carbon isotope technique, deemed to be a feasible and very effective method, has been widely used (Sugimoto and Wada, 1993;Chanton et al, 1997;Tyler et al, 1997;Bilek et al, 1999;Krüger et al, 2002;Conrad and Klose, 2005). Relative contribution of the two methanogenic pathways and proportion of CH 4 oxidized in the field can be estimated if δ 13 C-values of CH 4 , CO 2 and acetate are measured and relevant fractionation factors (ε acetate , α CO 2 /CH 4 , α ox and ε transport ) are known.…”

“…Relative contribution of the two methanogenic pathways and proportion of CH 4 oxidized in the field can be estimated if δ 13 C-values of CH 4 , CO 2 and acetate are measured and relevant fractionation factors (ε acetate , α CO 2 /CH 4 , α ox and ε transport ) are known. The carbon isotope fractionation factors of CH 4 oxidation (α ox ) and CH 4 transport (ε transport ) are crucial to the quantification of the fraction of CH 4 oxidized in applying the stable carbon isotope technique (Tyler et al, 1997;Bilek et al, 1999;Krüger et al, 2002;Zhang et al, 2009). Therefore, the acquisition of reliable and exact fractionation factors (α ox and ε transport ) is an important precondition for use of the method in studying CH 4 oxidation.…”

“…Previous studies mainly focused on fractionation factor α ox in the landfill cover soils (see Chanton et al, 2008a, b), rather than in paddy soil (Krüger et al, 2002). Moreover, early reports showed that fractionation factor ε transport varied with rice growth and with rice variety as well (Chanton et al, 1997;Tyler et al, 1997;Bilek et al, 1999;Krüger et al, 2002). Further study is necessary to discuss the effect of straw incorporation on growth of rice plants and eventually on fractionation factors, α ox of paddy soil and ε transport of rice plants.…”