Observed and modelled ecosystem respiration and gross primary production of a grassland in southwestern France

[摘要] In this work, the rich dataset acquired at the SMOSREX experimentalsite is used to enhance the A-gs version of the Interactions betweenSoil, Biosphere and Atmosphere (ISBA) model. A simple representationof the soil moisture effect on the ecosystem respiration isimplemented in the ISBA-A-gs model. It results in an improvement ofthe modelled CO₂ flux over a grassland in southwestern France.The former temperature-only dependent respiration formulation usedin ISBA-A-gs is not able to model the limitation of the respirationunder dry conditions. In addition to soil moisture and soiltemperature, the only parameter required in this formulation is theecosystem respiration parameter Re₂₅. It can be estimated bymeans of eddy covariance measurements of turbulent nighttimeCO₂ flux (i.e. ecosystem respiration). The resultingcorrelation between observed and modelled net ecosystem exchange isr²=0.63 with a bias of−2.18 μmol m⁻² s⁻¹. It is shown that whenCO₂ observations are not available, it is possible to use amore complex model, able to represent the heterotrophic respirationand all the components of the autotrophic respiration, to estimateRe₂₅ with similar results. The modelled ecosystem respirationestimates are provided by the Carbon Cycle (CC) version of ISBA(ISBA-CC). ISBA-CC is a version of ISBA able to simulate all therespiration components, whereas ISBA-A-gs uses a single equation forecosystem respiration. ISBA-A-gs is easier to handle and moreconvenient than ISBA-CC for the practical use in atmospheric orhydrological models. Surface water and energy flux observations, aswell as Gross Primary Production (GPP) estimates, are compared withmodel outputs. The dependence of GPP to air temperature isinvestigated. The observed GPP is less sensitive to temperature thanthe modelled GPP. Finally, the simulations of the ISBA-A-gs modelare analysed over a seven year period (2001–2007). Modelled soilmoisture and Leaf Area Index (LAI) are confronted with the observedsurface and root-zone soil moisture content (m³ m⁻³), andwith LAI estimates derived from surface reflectance measurements.

[学科分类] 地球化学与岩石