An experiment of Artificial Ecosystem in closed growth chambers is described. It comprises a biomass producer compartment coupled with a decomposer compartment. A model of carbon cycle is presented, simulating the CO2 changes in atmosphere and the carbon status in plants and in the decomposer system. Results of variation in several parameters such as photoperiod, rate of photosynthesis, percentage of harvested biomass introduced in decomposer, kinetics of biomass decomposition, are presented. Positive conclusions are deduced about the feasability of real experiments without particular control of CO2 nor buffering system. Applications in studies on plant-soil-atmosphere ecosystems, for spatial and terrestrial researches, are discussed.