In situ measurements of carbon dioxide gradients in a soil-plant-atmosphere system.

In order to more fully understand carbon dioxide dynamics in a soil-plant-atmosphere system, an in situ sampling technique has been developed to measure carbon dioxide concentration within the soil profile as well as in the atmosphere. Gas samples are automatically pumped in sequence from six porous collectors within the soil profile and five aboveground inlets through an infrared gas analyzer. Field measurements in a first year field, indicated that carbon dioxide concentrations reached a maximum value (∼1800 ppm) in the deepest soil sampling site (-180 cm). Temporal and spatial variations of carbon dioxide concentration were related to the development of root and vegetation structure as well as the position of the groundwater table.