Changes in concentration and? 13C values of soil-trapped CH4 and C02 in flooded rice soil

Abstract

Pot experiments were conducted to monitor the changes in compositions and δ13C values of soil-trapped CH4 and C02 in flooded rice soil with and without rice plants or rice straw. Incorporation of rice straw increased the concentration of CH4 and C02 accumulated in soil, and the quantities of emitted CH4 to the atmosphere. Rice plants reduced the concentration of soil-trapped CH4 and CO2, and the decreased portion of CH4 was replaced by N2. A significantly negative correlation was found between soil-trapped CH4 and N2. The presence of rice plants increased the δ13C values of CH4. The δ13C values of CH4 tended to increase toward the end of the growing season and were positively correlated with concentration of soil-trapped CH4. A positive correlation between δ13C values of CH4 and C02, and between the δ13C values of CH4 and its concentration, were observed. The CH4 in the rice stems was 4–14% enriched in13C relative to soil-trapped CH4. In contrast, CO2 in rice plant stems was 1–9% lighter in13C relative to soil-trapped C02. These results are discussed in relation to the precursor pools and pathways of methanogenesis.