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DIVISION S-3-SOIL BIOLOGY & BIOCHEMISTRY

Dynamics of Dissolved Organic Carbon and Methane Emissions in a Flooded Rice Soil

^a Laboratory of Soil Biology and Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601 Japan
^b Fraunhofer Institute for Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany
^c UFZ-Center for Environmental Research, Department of Soil Sciences, Theodor-Lieser Strasse 4, D-06120 Halle, Germany
^d College of Resources and Environmental Sciences, Zhejiang University, Zhejiang, China

lyahai{at}nuagr1.agr.nagoya-u.ac.jp

Limited information is available on the dynamics of dissolved organic C (DOC) and its relationship with CH₄ emissions in flooded rice (Oryza sativa L.) soils as affected by rice cultivar. Greenhouse and laboratory experiments were conducted to determine root C release in culture solution, DOC and dissolved CH₄ concentration in soil solution, and CH₄ emission in a flooded soil planted with three rice cultivars. Soil solutions were sampled in the root zone (soil surrounding rice roots) and the non-root zone (soil outside the root zone). The release of root exudates increased in the order: IR65598 (new plant type) < IR72 (modern cultivar) < Dular (a traditional cultivar). Correspondingly, DOC concentrations in the root zone and CH₄ emission rates increased. The dynamics of DOC and dissolved CH₄ differed greatly between the root zone and the non-root zone. Dissolved organic C in the root zone increased with plant growth and reached maximum (13–24 mmol C L^-1) between rice flowering and maturation (Week 11–13), whereas DOC in the non-root zone remained low (1–5 mmol C L^-1) throughout the growing season. Similarly, dissolved CH₄ concentrations in the root zone increased sooner and were greater (mean 138 µmol CH₄ L^-1) than those in the non-root zone (mean 97 µmol CH₄ L^-1). The seasonal patterns of CH₄ emissions closely followed the dynamics of DOC concentrations in the root zone. The results suggest that (i) DOC pool in the root zone of rice plants is enriched by root-derived C; (ii) the rates of CH₄ emissions are positively correlated with the dynamics of DOC in the root zone; (iii) the intercultivar difference in root C releases is responsible for the intercultivar difference in DOC production, and consequently in CH₄ flux.

Abbreviations: DOC, dissolved organic C • GC, gas chromatograph • PI, panicle initiation • SOC, soil organic C

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