Integrating peatlands and permafrost into a dynamicglobal vegetation model:2. Evaluation and sensitivity of vegetation and carbon cycle processes

摘要

Peatlands and permafrost are important components of the carbon cycle in thenorthern high latitudes. The inclusion of these components into a dynamic globalvegetation model required changes to physical land surface routines, the addition oftwo new peatland-specific plant functional types, incorporation of an inundation stress mechanism, and deceleration of decomposition under inundation. The new model,LPJ-WHy v1.2, was used to simulate net ecosystem production (NEP), net primaryproduction (NPP), heterotrophic respiration (HR), and soil carbon content. Annualpeatland NEP matches observations even though the seasonal amplitude is overestimated.This overestimation is caused by excessive NPP values, probably due to the lack ofnitrogen or phosphorus limitation in LPJ-WHy. Introduction of permafrost reducescircumpolar (45-90°N) NEP from 1.65 to 0.96 Pg C a-1 and leads to an increase in soilcarbon content of almost 40 Pg C; adding peatlands doubles this soil carbon increase.Peatland soil carbon content and hence HR depend on model spin-up duration and arecrucial for simulating NEP. These results highlight the need for a regional peatlandage map to help determine spin-up times. A sensitivity experiment revealed thatunder future climate conditions, NPP may rise more rapidly than HR resulting inincreases in NEP.