文摘
Isotopic net ecosystem exchange (isofluxes, or flux densities of 13CO2) can be combined with standard eddy covariance methods to partition net ecosystem exchange of carbon dioxide (F) into its component one-way fluxes, photosynthesis and respiration. At present, the approaches used to estimate isotopic fluxes are labor-intensive and dependent on several assumptions. To assess the relative utility of the available methods, we studied an ecosystem associated with large CO2 fluxes and maximal isotopic exchange. Three independent techniques were used to measure isotopic flux densities over an irrigated alfalfa field: (1) a combination of standard eddy covariance and flask sampling; (2) the flux-gradient method; and (3) hyperbolic relaxed eddy accumulation (HREA). Consistent isotopic flux results were obtained via the three methods, with similar diurnal patterns and peak midday isotopic flux densities of 600–700μmolm−2s−1‰.