Modelling nitrogen mineralization and plant nitrogen uptake as affected by reclamation cover depth in reclaimed upland forestlands of Northern Alberta

Early forest re-establishment in landforms constructed from materials such as overburden or mine waste is partly determined by nitrogen (N) availability in reclamation covers. Here we examined whether the ecosystem model ecosys which simulates key processes governing N availability such as mineralization, plant N uptake and N return to soil through litterfall could be used to forecast potential N limitations for forest re-establishment in these constructed landforms. In this study, N cycling was simulated and tested against measured soil, foliar and surface litter N concentrations with three soil covers differing in thickness (35, 50, and 100 cm) in a 17-year-old forest reclamation site and in an analogue natural forested site in northern Alberta. Overall, results from this study demonstrated the applicability of the ecosys model in predicting nutrient cycling in reclaimed upland forestlands. Results of this study highlight the importance of optimum cover depth to ensure sufficient N is available for plant growth. Even though the modelled net N mineralization, N uptake and thereby plant productivity increased with cover depth, the foliar and surface litter N concentrations did not. A non-linear relationship between total soil nitrogen (TN) stocks and modelled net N mineralization indicated that cover depth, which determines TN stock, had little effect on net primary productivity beyond a threshold TN. This threshold was 17 Mg N ha−1, similar to TN for the 100 cm cover, giving a net N mineralization rate of ~ 3.5 g N m−2 year−1, and this was attributed to reduced microbial activity in deeper soil layers.