Partitioning NEE for absolute C input into various ecosystem pools by combining results from eddy-covariance, atmospheric flux partitioning and 13CO2 pulse labeling

The complexity of ecosystem processes, especially under continuously changing environmental conditions, requires high-resolution insight into ecosystem carbon (C) fluxes. It is essential to gain not only information about relative C balance and fluxes (common for partitioning studies), but also to obtain these in absolute mass units. To evaluate absolute fluxes in belowground C pools, the results of 21-day eddy-covariance and stable isotope labeling experiment in summer 2010, were combined. Eddy-covariance based net ecosystem exchange was measured on extensively managed grassland and separated into underlying assimilation and ecosystem respiration through the use of a C flux partitioning model. Resultant CO 2 assimilation served as absolute C input into the ecosystem and was further partitioned by applying the relative C distribution in subsidiary pools, gained by 13 C pulse labeling and tracing. The results form eddy-covariance measurements showed that the extensively managed grassland was a significant net C sink of −91 g C m −2 a −1 in 2010. The mean daily assimilation of −7.1 g C m −2 d −1 was partitioned into fluxes of 2.5, 0.8, 0.5, 2.3 and 1.0 g C m −2 d −1 into shoots, roots, soil, shoot respiration and CO 2 efflux from soil, respectively. We conclude that the combination of EC measurements with isotope labeling techniques allowed determining the absolute C input into several ecosystem pools. Hence, the study demonstrates an approach to expand atmospheric flux measurements and to gain insight into the importance of individual ecosystem pools for soil C cycling.