Journal
AGRICULTURAL AND FOREST METEOROLOGY
Volume 249, Issue -, Pages 434-443Publisher
ELSEVIER
DOI: 10.1016/j.agrformet.2017.10.028
Keywords
Net ecosystem exchange (NEE); Soil CO2 efflux; Temperature sensitivity; Q(10); Eddy covariance; AmeriFlux; FLUXNET
Categories
Funding
- National Science Foundation [1137178]
- NASA under Carbon Monitoring Systems [NNX13AQ06G]
- US Department of Agriculture [2014-67003-22070]
- Austrian Science fund (FWF) [P17560-B16, P18756-B16, P22214-B17]
- Academy of Finland Finnish Center of Excellence Program [272041]
- CONACyT
- Life Sciences Program of CICESE
- Office of Science of the U.S. Department of Energy, Terrestrial Ecosystem Sciences Program
- NASA [465804, NNX13AQ06G] Funding Source: Federal RePORTER
- NIFA [688554, 2014-67003-22070] Funding Source: Federal RePORTER
- Direct For Biological Sciences
- Emerging Frontiers [1137178] Funding Source: National Science Foundation
- Austrian Science Fund (FWF) [P 26425] Funding Source: researchfish
- Austrian Science Fund (FWF) [P17560, P18756] Funding Source: Austrian Science Fund (FWF)
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The net ecosystem exchange (NEE) is the difference between ecosystem CO2 assimilation and CO2 losses to the atmosphere. Ecosystem respiration (R-eco), the efflux of CO2 from the ecosystem to the atmosphere, includes the soil-to-atmosphere carbon flux (i.e., soil respiration; R-soil) and aboveground plant respiration. Therefore, R-soil is a fraction of R-eco and theoretically has to be smaller than R-eco at daily, seasonal, and annual scales. However, several studies estimating R-eco with the eddy covariance technique and measuring R-soll within the footprint of the tower have reported higher R-soil than R-eco, 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 R-eco are consistently higher than R-soil. In general, both fluxes showed similar temporal patterns, but R-eco, was not consistently higher than R-soil from daily to annual scales across sites. We identified several issues that apply for measuring NEE and measuring/upscaling R-soil that could result in an underestimation of R-eco and/or an overestimation of R-soil. These issues are discussed based on (a) nighttime measurements of NEE, (b) R-soil measurements, and (c) the interpretation of the functional relationships of these fluxes with temperature (i.e., Q(10)). We highlight that there is still a need for better integration of R-soil with eddy covariance measurements to address challenges related to the spatial and temporal variability of R-eco, and R-soil.
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