Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

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anglais. In this study we examined ecosystem respiration (RECO) data from 104 sites belonging to FLUXNET, the globalnetwork of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability ofRECO: temporally and between sites as affected by climate, vegetation structure and plant functional type (PFT)(evergreen needleleaf, grasslands, etc.). We demonstrated that a model using only climate drivers as predictors ofRECO failed to describe part of the temporal variability in the data and that the dependency on gross primaryproduction (GPP) needed to be included as an additional driver of RECO. The maximum seasonal leaf area index(LAIMAX) had an additional effect that explained the spatial variability of reference respiration (the respiration atreference temperature Tref515 1C, without stimulation introduced by photosynthetic activity and without waterlimitations), with a statistically significant linear relationship (r250.52, Po0.001, n5104) even within each PFT.Besides LAIMAX, we found that reference respiration may be explained partially by total soil carbon content (SoilC).For undisturbed temperate and boreal forests a negative control of total nitrogen deposition (Ndepo) on referencerespiration was also identified. We developed a new semiempirical model incorporating abiotic factors (climate),recent productivity (daily GPP), general site productivity and canopy structure (LAIMAX) which performed well inpredicting the spatio-temporal variability of RECO, explaining 470% of the variance for most vegetation types.Exceptions include tropical and Mediterranean broadleaf forests and deciduous broadleaf forests. Part of thevariability in respiration that could not be described by our model may be attributed to a series of factors, includingphenology in deciduous broadleaf forests and management practices in grasslands and croplands.