Abstract
Abstract. In this work, the rich dataset acquired at the SMOSREX experimental site is used to enhance the A-gs version of the Interactions between Soil, Biosphere and Atmosphere (ISBA) model. A simple representation of the soil moisture effect on the ecosystem respiration is implemented in the ISBA-A-gs model. It results in an improvement of the modelled CO2 flux over a grassland in southwestern France. The former temperature-only dependent respiration formulation used in ISBA-A-gs is not able to model the limitation of the respiration under dry conditions. In addition to soil moisture and soil temperature, the only parameter required in this formulation is the ecosystem respiration parameter Re25. It can be estimated by means of eddy covariance measurements of turbulent nighttime CO2 flux (i.e. ecosystem respiration). The resulting correlation between observed and modelled net ecosystem exchange is r2=0.63 with a bias of −2.18 μmol m−2 s−1. It is shown that when CO2 observations are not available, it is possible to use a more complex model, able to represent the heterotrophic respiration and all the components of the autotrophic respiration, to estimate Re25 with similar results. The modelled ecosystem respiration estimates are provided by the Carbon Cycle (CC) version of ISBA (ISBA-CC). ISBA-CC is a version of ISBA able to simulate all the respiration components, whereas ISBA-A-gs uses a single equation for ecosystem respiration. ISBA-A-gs is easier to handle and more convenient than ISBA-CC for the practical use in atmospheric or hydrological models. Surface water and energy flux observations, as well as Gross Primary Production (GPP) estimates, are compared with model outputs. The dependence of GPP to air temperature is investigated. The observed GPP is less sensitive to temperature than the modelled GPP. Finally, the simulations of the ISBA-A-gs model are analysed over a seven year period (2001–2007). Modelled soil moisture and Leaf Area Index (LAI) are confronted with the observed surface and root-zone soil moisture content (m3 m−3), and with LAI estimates derived from surface reflectance measurements.
Highlights
A major component of the global carbon balance is the flux of CO2 from the soil, referred to as soil respiration (Raich et al, 2002; Schlesinger et al, 2000)
The Re25 values of Eqs. (4) and (1) were set to 5.22 μmol m−2 s−1 and 3.63 μmol m−2 s−1, respectively, by minimising the Root Mean Square Error (RMSE) between the ecosystem respiration derived from Eqs. (4) and (1) and the observed filtered values of CO2 measurements
Another calibration of Eqs. (4) and (1) was done with Reco modelled by ISBA-CC, and gave similar results: Re25 best-fit values of 5.00 μmol m−2 s−1 for Eq (4) and 3.18 μmol m−2 s−1 for Eq (1)
Summary
A major component of the global carbon balance is the flux of CO2 from the soil, referred to as soil respiration (Raich et al, 2002; Schlesinger et al, 2000). It is a major source of CO2 entering the atmosphere (20–40% of the total flux, Kicklighter et al, 1994). Various models have been proposed to describe soil respiration and Reco They are based on temperature-dependent relations (Katterer et al, 1998; Kirschbaum et al, 1995; Lloyd and Taylor, 1994) combined
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
