The ability of contrasting ericaceous ecosystems to buffer nitrogen leaching

Much attention has been given to the carbon balance of peatland and heathland ecosystems and their role as global carbon stores. They are also important as buffers for atmospheric nitrogen (N) pollution, locking N into the soil and vegetation through tight nutrient cycling and preventing the leaching of soluble N into freshwater ecosystems. We compared mean annual soil exchangeable N, mineralisation and soil solution nitrogen at three contrasting ericaceous-dominated ecosystems: a lowland heath, an upland heath and an ombrotrophic raised bog at intermediate altitude, all of which were sites of long-term N-manipulation experiments. We expected that soil leachate N would be associated with soil C/N and total soil C, and that sites with higher C % and soil C/N would have greater ability to buffer N deposition before N saturation and leaching began. However, although soil solution N responded to N deposition at all the sites, we found that only the heathland sites were consistent with this expectation. The bog, with the highest C/N and largest C pool, was not the most strongly buffered. The upland heath was most effective at retaining N (extractable NH4+-N +3900 % from control) compared to the lowland heath (extractable NH4+-N +370 % from control) and the bog (extractable NH4+-N, +140–240 % from control). We concluded that the absence of a definabl Calluna litter layer at the lowland heath and the bog, and the anoxic conditions at the bog, explained the earlier onset of leaching and that carbon and nitrogen cycles appeared more closely coupled in the heathlands but became decoupled at the bog due to the strong controlling effect of hydrology.