Use of micrometeorological techniques to study the isotopic exchange in ecosystems

Abstract:

The combination of micrometeorological techniques with high frequency concentration measurements of stable isotopes are a powerful tool to study the temporal dynamics of isotope signatures at the ecosystem level. The objective of this study was to study the isotopic composition of the net CO₂ exchange (NEE) above and with corn and tall grass canopies. Profiles of stable isotopes of CO₂ (¹²C-CO_2, ¹³C-CO₂ and ¹⁸O-CO₂) were measured using tunable diode laser trace gas analyzers and multiport sampling systems in corn (¹²C-CO₂ and ¹³C-CO₂, only) and tall grass canopies. These measurements were combined with the flux gradient method and Lagrangian dispersion analysis to estimate the isotopic signatures of the net CO₂ flux. The use of a gradient of a concentration threshold to screen half hourly period improved the estimates of flux signatures by the isotope flux ratio approach. The Langrangian dispersion analysis and the isotope flux ratio method estimates showed good agreement above the corn canopy, indicating that the former method can be a viable alternative to study the isotopic exchange within plant canopies. The ¹³CO₂ composition of NEE showed a downward trend near the end of the growing season, which may be related to a reduction of autotrophic respiration in the soil.