Reduced atmospheric CH₄ consumption by two forest soils under elevated CO₂ concentration in a FACE system in northern Japan

Abstract

At elevated atmospheric CO₂ concentrations, the soil CH₄ flux may be mediated by plant physiology, including the transpiration rate and water use efficiency. To investigate the effect of elevated CO₂ on atmospheric CH₄ consumption by well-drained forest soil, we measured the soil CH₄ flux at the Free Air CO₂ Enrichment (FACE) site of Hokkaido University during two growing seasons (2008 and 2009). Fumigation with CO₂ began in June 2003, since when the plots have either been exposed to ambient levels or enriched with CO₂ at 130 μL L^-1. We also studied two soil types, brown forest soil and volcanic ash soil, which are widely distributed in northern Japan. The soil CH₄ flux and soil water content were measured simultaneously on four occasions at monthly intervals during each growing season. In both types of soil, the elevated CO₂ plot experienced an approximately 50 % lower soil CH₄ consumption rate than in the ambient CO₂ plot. However, there was no significant difference in soil CH₄ consumption between two soil types. Regardless of the soil type, soil CH₄ consumption was observed at all measurement points in the ambient CO₂ plot, but approximately 13 % of all sampling points in the elevated CO₂ plot experienced net CH₄ production, suggesting that increases in soil moisture influence CH₄ oxidation at elevated CO₂ concentrations.