Comparison of N and C dynamics in two Norway spruce stands using a processoriented simulation model

Nitrogen and carbon dynamics of two Norway spruce stands were compared usin g a dynamic soil-plant simulation model (SOILN). The objectives were to eva luate differences in properties between the two stands and to explore the c onsequences on C and N dynamics. The young stand (25 years old) was located in south-west Sweden (Skogaby) growing on a loamy sand soil. The old stand (70 years old) was growing on a sandy soil in western Denmark (Klosterhede ). Differences in specific rates of processes between the two sites were es timated in terms of parameter values derived by calibration of the model. D ifferences in daily flow rates and pathways of N and C were examined and bu dget components were simulated over a six year period. Simulations showed t hat the different stands had different specific rates for growth, allocatio n, litter fall and N uptake resulting in higher N uptake in the younger tre es whereas growth was more similar. The soil carbon balance was positive an d soil CIN ratio increased for the young stand. For the old stand the soil carbon balance was negative and the C/N ratio decreased. The soil mineral N levels were much lower in the younger stand which was explained by a highe r plant uptake of organic N. At both sites the average pools and fluxes ove r the years were fairly well simulated indicating that N leaching predictio ns on average might be reliable.