Advanced

Separation of net ecosystem exchange into assimilation and respiration using a light response curve approach: critical issues and global evaluation

Lasslop, Gitta; Reichstein, Markus; Papale, Dario; Richardson, Andrew D.; Arneth, Almut LU ; Barr, Alan; Stoy, Paul and Wohlfahrt, Georg (2010) In Global Change Biology 16(1). p.187-208
Abstract
The measured net ecosystem exchange (NEE) of CO2 between the ecosystem and the atmosphere reflects the balance between gross CO2 assimilation [gross primary production (GPP)] and ecosystem respiration (R-eco). For understanding the mechanistic responses of ecosystem processes to environmental change it is important to separate these two flux components. Two approaches are conventionally used: (1) respiration measurements made at night are extrapolated to the daytime or (2) light-response curves are fit to daytime NEE measurements and respiration is estimated from the intercept of the ordinate, which avoids the use of potentially problematic nighttime data. We demonstrate that this approach is subject to biases if the effect of vapor... (More)
The measured net ecosystem exchange (NEE) of CO2 between the ecosystem and the atmosphere reflects the balance between gross CO2 assimilation [gross primary production (GPP)] and ecosystem respiration (R-eco). For understanding the mechanistic responses of ecosystem processes to environmental change it is important to separate these two flux components. Two approaches are conventionally used: (1) respiration measurements made at night are extrapolated to the daytime or (2) light-response curves are fit to daytime NEE measurements and respiration is estimated from the intercept of the ordinate, which avoids the use of potentially problematic nighttime data. We demonstrate that this approach is subject to biases if the effect of vapor pressure deficit (VPD) modifying the light response is not included. We introduce an algorithm for NEE partitioning that uses a hyperbolic light response curve fit to daytime NEE, modified to account for the temperature sensitivity of respiration and the VPD limitation of photosynthesis. Including the VPD dependency strongly improved the model's ability to reproduce the asymmetric diurnal cycle during periods with high VPD, and enhances the reliability of R-eco estimates given that the reduction of GPP by VPD may be otherwise incorrectly attributed to higher R-eco. Results from this improved algorithm are compared against estimates based on the conventional nighttime approach. The comparison demonstrates that the uncertainty arising from systematic errors dominates the overall uncertainty of annual sums (median absolute deviation of GPP: 47 g C m(-2) yr(-1)), while errors arising from the random error (median absolute deviation: similar to 2 g C m(-2) yr(-1)) are negligible. Despite site-specific differences between the methods, overall patterns remain robust, adding confidence to statistical studies based on the FLUXNET database. In particular, we show that the strong correlation between GPP and R-eco is not spurious but holds true when quasi-independent, i.e. daytime and nighttime based estimates are compared. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
response curve, hyperbolic light, GPP, FLUXNET, eddy covariance, flux partitioning, R-eco, uncertainty
in
Global Change Biology
volume
16
issue
1
pages
187 - 208
publisher
Wiley-Blackwell
external identifiers
  • wos:000274419200016
  • scopus:70749099583
ISSN
1354-1013
DOI
10.1111/j.1365-2486.2009.02041.x
project
MERGE
BECC
language
English
LU publication?
yes
id
cb29bcc7-abd9-4a49-875c-238df9878a7d (old id 1570775)
date added to LUP
2010-03-17 08:13:41
date last changed
2018-07-15 03:23:42
@article{cb29bcc7-abd9-4a49-875c-238df9878a7d,
  abstract     = {The measured net ecosystem exchange (NEE) of CO2 between the ecosystem and the atmosphere reflects the balance between gross CO2 assimilation [gross primary production (GPP)] and ecosystem respiration (R-eco). For understanding the mechanistic responses of ecosystem processes to environmental change it is important to separate these two flux components. Two approaches are conventionally used: (1) respiration measurements made at night are extrapolated to the daytime or (2) light-response curves are fit to daytime NEE measurements and respiration is estimated from the intercept of the ordinate, which avoids the use of potentially problematic nighttime data. We demonstrate that this approach is subject to biases if the effect of vapor pressure deficit (VPD) modifying the light response is not included. We introduce an algorithm for NEE partitioning that uses a hyperbolic light response curve fit to daytime NEE, modified to account for the temperature sensitivity of respiration and the VPD limitation of photosynthesis. Including the VPD dependency strongly improved the model's ability to reproduce the asymmetric diurnal cycle during periods with high VPD, and enhances the reliability of R-eco estimates given that the reduction of GPP by VPD may be otherwise incorrectly attributed to higher R-eco. Results from this improved algorithm are compared against estimates based on the conventional nighttime approach. The comparison demonstrates that the uncertainty arising from systematic errors dominates the overall uncertainty of annual sums (median absolute deviation of GPP: 47 g C m(-2) yr(-1)), while errors arising from the random error (median absolute deviation: similar to 2 g C m(-2) yr(-1)) are negligible. Despite site-specific differences between the methods, overall patterns remain robust, adding confidence to statistical studies based on the FLUXNET database. In particular, we show that the strong correlation between GPP and R-eco is not spurious but holds true when quasi-independent, i.e. daytime and nighttime based estimates are compared.},
  author       = {Lasslop, Gitta and Reichstein, Markus and Papale, Dario and Richardson, Andrew D. and Arneth, Almut and Barr, Alan and Stoy, Paul and Wohlfahrt, Georg},
  issn         = {1354-1013},
  keyword      = {response curve,hyperbolic light,GPP,FLUXNET,eddy covariance,flux partitioning,R-eco,uncertainty},
  language     = {eng},
  number       = {1},
  pages        = {187--208},
  publisher    = {Wiley-Blackwell},
  series       = {Global Change Biology},
  title        = {Separation of net ecosystem exchange into assimilation and respiration using a light response curve approach: critical issues and global evaluation},
  url          = {http://dx.doi.org/10.1111/j.1365-2486.2009.02041.x},
  volume       = {16},
  year         = {2010},
}