Negative impact of nitrogen deposition on soil buffering capacity

Anthropogenic nitrogen deposition over the past half century has had a detrimental impact on temperate ecosystems in Europe and North America, resulting in soil acidification and a reduction in plant biodiversity(1,2). During the acidification process, soils release base cations, such as calcium and magnesium, neutralizing the increase in acidity. Once these base cations have been depleted, aluminium is released from the soils, often reaching toxic levels. Here, we present results from a nitrogen deposition experiment that suggests that a long legacy of acid deposition in the Western Tatra Mountains of Slovakia has pushed soils to a new threshold of acidification usually associated with acid mine drainage soils. We show that increases in nitrogen deposition in the region result in a depletion of both base cations and soluble aluminium, and an increase in extractable iron concentrations. In conjunction with this, we observe a nitrogen-deposition-induced reduction in the biomass of vascular plants, associated with a decrease in shoot calcium and magnesium concentrations. We suggest that this site, and potentially others in central Europe, have reached a new and potentially more toxic level of soil acidification in which aluminium release is superseded by iron release into soil water.