Abstract
The net ecosystem exchange (NEE) is the difference between ecosystem CO2 assimilation and CO2 losses to the atmosphere. Ecosystem respiration (Reco), the efflux of CO2 from the ecosystem to the atmosphere, includes the soil-to-atmosphere carbon flux (i.e., soil respiration; Rsoil) and aboveground plant respiration. Therefore, Rsoil is a fraction of Reco and theoretically has to be smaller than Reco at daily, seasonal, and annual scales. However, several studies estimating Reco with the eddy covariance technique and measuring Rsoil within the footprint of the tower have reported higher Rsoil than Reco at different time scales. Here, we compare four different and contrasting ecosystems (from forest to grasslands, and from boreal to semiarid) to test if measurements of Reco are consistently higher than Rsoil. In general, both fluxes showed similar temporal patterns, but Reco was not consistently higher than Rsoil from daily to annual scales across sites. We identified several issues that apply for measuring NEE and measuring/upscaling Rsoil that could result in an underestimation of Reco and/or an overestimation of Rsoil. These issues are discussed based on (a) nighttime measurements of NEE, (b) Rsoil measurements, and (c) the interpretation of the functional relationships of these fluxes with temperature (i.e., Q10). We highlight that there is still a need for better integration of Rsoil with eddy covariance measurements to address challenges related to the spatial and temporal variability of Reco and Rsoil.
Original language | English |
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Pages (from-to) | 434-443 |
Number of pages | 10 |
Journal | Agricultural and Forest Meteorology |
Volume | 249 |
DOIs | |
State | Published - Feb 15 2018 |
Funding
This study was supported by the National Science Foundation ( 1137178 ), NASA under Carbon Monitoring Systems ( NNX13AQ06G ), and US Department of Agriculture ( 2014-67003-22070 ). We acknowledge support from the Austrian Science fund (FWF) grants P17560-B16 , P18756-B16 and P22214-B17 , and the Academy of Finland Finnish Center of Excellence Program ( 272041 ). AC acknowledges support from a scholarship for his PhD studies, and support for an academic exchange with the University of Delaware provided by CONACyT and the Life Sciences Program of CICESE. BBL and PJH were supported by the Office of Science of the U.S. Department of Energy as part of the Terrestrial Ecosystem Sciences Program. Data used in this study are available at the AmeriFlux Data Repository, at the FLUXNET repository, or upon request.
Keywords
- AmeriFlux
- Eddy covariance
- FLUXNET
- Net ecosystem exchange (NEE)
- Q
- Soil CO efflux
- Temperature sensitivity