Acidifying processes and acid-base reactions in forest soils reciprocally transplanted along a European transect with increasing pollution

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Forest ecosystems are currently being exposed to changes in chemical inputs and it is suggested that physical climate is also changing. A novel approach has been used to study the effects of ionic inputs and climatic conditions on forest soils by reciprocally exchanging lysimeters containing undisturbed soil columns beween four forest sites in Europe. The soil columns contained no living roots and simulated a clear cut situation. The soils chosen represented different stages of acidification and were taken from sites along a transect of increasing exposure to acidic and nitrogen pollution. The purpose of the study was to quantify the reactions of soils when transferred to different environments. Element balances were used as an aggregated indicator to describe the reaction of the soil. The input of protons in local throughfall increased along the transect from 0.01 kmol ha−1 y−1 H+ at the unpolluted site up to 1.10 kmol ha−1 y−1 at the most polluted site. Our results show that soil acidification always resulted from a combination of acid deposition and biological transformations of nitrogen through nitrification of imported ammonium, mineralized N, or stored N. The balances indicate that between 54% and 91% of the soil acidification resulted from nitrification processes which were driven by a complex reaction when climatic and pollution conditions were changed simultaneously. The combined changes in atmosphic inputs and climatic conditions, as expected with global change, may have serious consequences for soil acidfication and long term organic matter turnover.

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