The Effects of Characteristics of Asian Monsoon Climate on Interannual CO₂ Exchange in a Humid Temperate C3/C4 Co-occurring Grassland

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CO₂ exchange was measured using eddy covariance technique during 2001, 2002, and 2003 in a humid temperate C3/C4 co-occurring grassland in Japan. The interannual variability in cloudiness of Asian monsoon will be an important forcing in CO₂ exchange. Early summer and autumn is a period with continuous rainy and cloudy days peculiar to the Asian monsoon region. The early summer rainy season (baiu) in 2001 ended earlier than 2002. In 2003, the baiu season was protracted, and the summer had cooler conditions than 2001 and 2002. Annual net ecosystem exchange was 9 gC m^-2 in 2001 and 17 gC m^-2 in 2003, and a weak CO₂ (-78 gC m^-2) sink in 2002. In 2002, the maximum annual gross primary production was 2426 gC m^-2, and contributed to negative net ecosystem CO₂ exchange. The annual variations of gross primary production and net ecosystem exchange were sensitive to that of photosynthetic photon flux density.