Acidification and alkalization of forest litters in Lithuania: effect on denitrification and nitrification

Abstract

The acidification and alkalization of forest soils, mainly in Scots pine (Pinus sylvestris L.) stands, clearly attributable to air pollution in Lithuania are observed in the vicinity of large industrial pollution sources. Chemical changes in forest litters are the most significant. As a consequence, the number of micro-organisms (mainly bacteria), that control the rate of denitrification and nitrification, is influenced. The impact of acidification on these processes was studied near the nitrogen fertilisers plant JV “Achema”. When at this location annual total nitrogen deposition had exceeded 90–120 kg ha-1 and sulphur 60–150 kg ha-1, the acidity of forest litter was pHKCl 3.4–3.8. As a result, the decrease in a number of nitrifiers up to about 2 times and the increase of the denitrifiers – up to 2–3 times was detected. The impact of alkalization was investigated in the vicinity of the cement plant JV “Akmenes cementas”. Here, due to the high cement dust emissions (annual wet deposition of Ca2+ and Mg2+ = 60–230 kg ha-1), alkalization of forest litters by 2.6–3.3 pHKCl up to pHKCl 6.3–7.0 was found. In contrast to the former case, the number of nitrifiers did not change here, while the number of denitrifiers, despite the low nitrogen deposition (10–15 kg ha-1 per year), had increased even by 30–60 times. The paper concludes that the alkalization significantly influences the abundance of the denitrifiers in forest litters.