Roots likely comprise the majority of the vascular plant biomass in arctic tundra ecosystems, yet their representation in arctic tundra vegetation and ecosystem models is often quite rudimentary and implicit, in large part due to the relative paucity of root biomass and turnover field data relative to the aboveground plant parts. Here we review the simulation of roots and root processes in some commonly used arctic tundra vegetation and ecosystem models, and conduct a sensitivity analysis of root nitrogen (N) uptake for specific plant functional types on the biomass composition of tundra plant communities, using the tundra vegetation dynamics model ArcVeg. ArcVeg uses a nitrogen-uptake efficiency parameter for simulating the root N uptake.
Results/Conclusions
A 57% increase in this parameter value for tussock sedges led to an over 3-fold increase in tussock sedge biomass, with minimal declines in the biomass of other plant functional types. A 57% decrease in tussock sedge N-uptake efficiency led to a 94% decline in tussock sedge biomass. A 57% increase in Low Arctic (LA) deciduous shrub N-uptake efficiency, led to a 45% increase in (LA) deciduous shrub biomass and a 65% decline in LA evergreen shrub biomass. A 57% decline in LA deciduous shrub N-uptake efficiency led to a 99% decline in LA deciduous shrub biomass and a 72% increase in LA evergreen shrub biomass. Therefore, whereas plant community composition in ArcVeg is highly sensitive to root N uptake, there are clearly non-linear responses to changes in this parameter, depending on the current community composition and the plant functional type for which root N uptake is changing. Finally, to identify some of the complexities of root structure and function on community biomass and composition, we use a newly developed analytical model, designed specifically to understand environmental change impacts on shrub growth and expansion in the arctic tundra.