Evaluation of recycling of respired CO₂ using stable isotope techniques

Abstract

Stable isotopes are a powerful research tool in ecosystem carbon balance studies and their use in ecosystem research is increasing. Stable isotope measurements together with CO₂ concentration and CO₂ flux measurements provide empirical means for understanding the processes that control CO₂ exchange between atmosphere –ecosystem and the mechanisms that govern patterns of carbon storage and release in terrestrial ecosystems. Combining stable isotopes and concentration measurements allows the identification of the isotopic composition and the contribution of ecosystem, or ecosystem components, to the exchange fluxes with the atmosphere. Recent modifications of stable isotope signatures of CO₂ along with CO₂ concentration measurements permit examination of CO₂ recycling within canopies (i.e., refixation of respiratory CO₂ before it leaves the system). Recycling of respired CO₂ can be possible factor that contributes to errors in partitioning net ecosystem exchange of CO₂ into photosynthetic assimilation and respiration using eddy covariance techniques and isotopic mass balance equations. Thus, the studies for CO₂ recycling are increasing during the several years. In this review, we introduce and discuss the relevant details underlying the use of carbon isotopic compositions in research for CO₂ recycling. To progress quantitative evaluations of CO₂ recycle in various ecosystems makes it possible to distinguish among the components contributed to the net CO₂ flux and to obtain insights into the processes underlying ecosystem responses to climate forcing.