In this study, a process-based model (RCG-C) was developed, parameterized and calibrated for studying the annual and seasonal dynamics of the ecosystem CO2 exchange (NEE) in a cutaway peatland (Linnansuo, eastern Finland) cultivated with a perennial bioenergy crop (Phalaris arundinaceae, L., RCG). Based on a number of prior studies and an environmentally controlled experiment, RCG-C emphasized several key processes beyond the generality of previous diplotelmic models for pristine peatlands. These processes included the effects of management (e.g., drainage, peat extraction, tilling, harvesting and fertilization) on the soil hydrology and the cycling of carbon and nitrogen, the influence of climatic factors on photosynthesis and the phenological cycle and phenological and soil-moisture controls on biomass production and canopy development. The model was validated based on continuous measurements of meteorological parameters, energy and CO2 fluxes (eddy covariance system) performed at the site from 2005 to 2010, including variation associated with both wet and dry years. The results showed that the model captured the seasonal and annual trends of the latent heat flux and NEE during the six-year period. Moreover, the simulated values for the total C sink capacity, accumulation of rhizome biomass and peat formation from RCG obtained during the six-year period also agreed well with the field measurements. Based on the FINADAPT climate scenarios, a sensitivity analysis of the model showed that the potential increases in the atmospheric CO2 concentration (Ca) and air temperature (Ta) could be the main forces driving the changes in NEE. The model simulation suggested that the effects of Ta tend to offset those of Ca and lead to a decrease in the total C sink capacity of the site during the main rotation period (4-15th year of cultivation). This decrease tends to become more intensive toward the end of the 21st century. During the period from 2060 to 2099, the total CO2 sink capacity could decrease by 79% during the main rotation period at the Linnansuo site.
