Interactive effects of nitrogen deposition and fire on plant and soil chemistry in an alpine heathland.

The response of alpine heathland vegetation and soil chemistry to N additions of 0, 10, 20 and 50 kg N ha(-1) year(-1) in combination with simulated accidental fire (+/-) was monitored over a 5-year period. N addition caused rapid and significant increases in plant tissue N content and N:P and N:K of Calluna vulgaris, suggesting increasing phosphorus and potassium limitation of growth. Soil C:N declined significantly with N addition, indicating N saturation and increasing likelihood of N leakage. Fire further decreased soil C:N and reduced potential for sequestration of additional N. This study shows that alpine heathlands, which occupy the headwaters of many rivers, have limited potential to retain deposited N and may rapidly become N saturated, leaking N into downstream communities and surface waters.