Dynamics of carbon dioxide in soil profiles based on long-term field observation.

Long-term field observation of carbon dioxide concentrations in soil air and soil temperature and moisture was conducted in a forested (oak and Japanese larch) headwater basin. The soil CO₂ concentration was measured monthly from the ground surface to a depth of 2 m using gas detection tubes. The data were then averaged monthly to show general annual trends. The temporal and spatial distribution of carbon dioxide showed generally constant annual patterns of concentration increase from spring to summer and decrease from autumn to winter in response to soil temperature changes. The concentration increased exponentially with soil temperature ≥5 ^°C at the same depth, suggesting a close relationship between the concentration and production of carbon dioxide. From late winter to early spring a frozen layer formed at the top of the soil profile that inhibited the escape of carbon dioxide into the atmosphere. The soil CO₂ concentrations in the oak forest were generally higher than those in the Japanese larch forest, although both soil respiration rate and soil organic carbon contents were lower in the oak forest. Considerable interannual differences in the distribution of carbon dioxide were observed with coincident differences in precipitation. Concentrations at shallow depths were relatively low in dry summers. When the frozen layer was not formed under thick snow cover, soil CO₂ concentration did not increase. In deep soils, where the influence of precipitation was not significant, the interannual difference was almost always within ±20% of the monthly average. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]