Interactions of ecosystem processes with spatial heterogeneity in the puzzle of nitrogen limitation

We examined the potential effects of spatial heterogeneity and its development on the distribution, abundance, and functioning of nitrogen fixing and non-fixing components of a model ecosystem. CAECO, a spatially explicit individual based model approach, simulated the interactions between nitrogen fluxes and plant species community dynamics. Self-organized spatial patterns of nitrogen concentrations and plant occupancy were observed as the system approached an apparently meta-stable state. Nitrogen limitation was tested using chronic and gradient nitrogen amendments to the landscape. The dynamic arrangement of ecosystem components was sufficient to maintain indefinite nitrogen limitation at a local scale. However, landscape scale productivity was not similarly increased with nitrogen amendments. Landscape productivity was independent of nitrogen additions while fixers were present in the ecosystem. The probability of fixer loss from the system responded non-linearly to increasing nitrogen addition. The results of these model experiments suggest local and landscape constraints of primary productivity may be fundamentally distinct.