Effects of rice cultivars on methane fluxes in a paddy soil

CH4 emission and its relevant processes involved (i.e. CH4 production, rhizospheric CH4 oxidation and plant-mediated CH4 transport) were studied simultaneously to comprehensively understand how rice cultivars (Yanxuan, 72031, and 9516) at growth stages (early and late tillering, panicle initiation, ripening, and harvest stage) affect CH4 emission in a paddy soil. Over the entire rice-growing season, Yanxuan had the highest CH4 emission flux with 5.98 mug CH4 m(-2) h(-1) followed by 72031 (4.48 mug CH4 m(-2) h(-1)) and 9516 (3.41 mug CH4 m(-2) h(-1)). The highest CH4 production rate of paddy soils planted to Yanxuan was observed with 18.0 mug CH4 kg((d.w.soil) h(-1) followed by the soil planted to 9516 (17.5 mug CH4 kg((d.w.soil)) h(-1)). For each cultivar, both rhizospheric CH4 oxidation ability and plant-mediated CH4 transport efficiency varied widely with a range of 9.81-76.8% and 15.5-80.5% over the duration of crop growth, respectively. Multiple regression analyses showed that CH4 emission flux was positively related with CH4 production rate and rice plant-mediated CH4 transport efficiency, but negatively with rhizospheric CH4 oxidation (R-2 = 0.425 for Yanxuan, P< 0.01; R-2 = 0.426 for 72031, P< 0.01; R-2 = 0.564 for 9516, P< 0 01). The contribution of rice plants to CH4 production seems to be more important than to rhizospheric CH4 oxidation and plant-mediated transport in impact of rice plants on CH4 emission.