Temporal Dynamics of Oxygen Isotope Compositions of Soil and Canopy CO2 Fluxes in a Temperate Deciduous Forest

The stable isotopomer of CO2, C18OO, is a valuable tracer and have been used to study the CO2 exchange in different spatial scales. The objectives of this study were: to quantify the magnitude of isotopic desiquilibrium (Deq) in a temperate deciduous forest throughout the growing season, and to determine the sensitivity of Deq to CO2 hydration efficiency. In this study, C18OO and H218O composition of the air were measured quasi-continuously and simultaneously above a temperate deciduous forest using tunable diode laser trace gas analyzers. In addition, detailed measurements of H218O composition of ecosystem water pools were performed throughout the experimental period. These field measurements were used with existing formulations to estimate the C18OO of soil (δR) and canopy (δR) CO2 fluxes. Values of δA also showed large day to day variation in our site. The dynamics of δR was mainly driven by changes in soil water isotope composition, caused by precipitation events. The magnitude of Deq was variable throughout the season and very sensitive to the extent of the CO2 hydration in the canopy. In this ecosystem, for most of the growing season, the magnitude of Deq was inversely proportional to θeq. This can be explained by the very negative δR signal in our ecosystem.