CH4 production potential in a paddy soil exposed to atmospheric CO2 enrichment

Abstract

An anaerobic incubation experiment was conducted to investigate methane (CH₄) production potential in soil samples collected from a paddy field after exposure to free-air CO₂ enrichment (FACE). The FACE experiment with two CO₂ levels, ambient and ambient + 200 p.p.m.v CO₂ during the rice growing season, was conducted at Shizukuishi, Iwate Prefecture, Japan. The soil was a wet Andosol. Soil samples were taken from the surface (0–1 cm) and the sub-surface (1–10 cm) soil layers 2 months after rice harvest. Sub-samples of the fresh soils were put into glass bottles and submerged under N₂ gas headspace during the incubation. The results showed that, prior to incubation, the contents of total C and dissolved organic C (DOC) were significantly greater in FACE soil than ambient soil. During the incubation, CH₄ production potential was approximately 2–4-fold higher in FACE soil than ambient soil and approximately 500–1,000-fold greater in surface soil than sub-surface soil. In general, the FACE soil contained more DOC than ambient soil, particularly in the surface soil layer. These findings suggest that FACE treatment exerted long-term positive effects on CH₄ production and increased organic C content in this paddy soil, particularly in the surface soil layer.