The role of respiration in estimation of carbon cycle

Understanding the dynamics of organic carbon mineralization is fundamental in forecastingbiosphere to atmosphere net carbon ecosystem exchange (NEE). With this perspective, we developed3D-CMCC-PSM, a new version of the hybrid process based model 3D-CMCC FEM where alsoheterotrophic respiration (R h ) is explicitly simulated. The aim was to quantify NEE as a forwardproblem, by subtracting ecosystem respiration (R eco ) to gross primary productivity (GPP). To doso, we developed a simplification of the soil carbon dynamics routine proposed in the DNDC(DeNitrification-DeComposition) computer simulation model. The method calculates decompositionas a function of soil moisture, temperature, state of the organic compartments, and relative abundanceof microbial pools. Given the pulse dynamics of soil respiration, we introduced modificationsin some of the principal constitutive relations involved in phenology and littering sub-routines.We quantified the model structure-related uncertainty in NEE, by running our training simulationsover 1000 random parameter-sets extracted from parameter distributions expected from literature.3D-CMCC-PSM predictability was tested on independent time series for 6 Fluxnet sites. The modelresulted in daily and monthly estimations highly consistent with the observed time series. It showedlower predictability in Mediterranean ecosystems, suggesting that it may need further improvementsin addressing evapotranspiration and water dynamics.