Implications of acidified S inputs on the fate and consequences of N deposition: results from a field manipulation of a Sitka spruce canopy in Southern Scotland

This paper describes a field manipulation experiment where the effects of a simulated decline in acidified S inputs on the fate of N on Sitka spruce growing on an organo-mineral soil were investigated, along side those of the original treatments: ammonium nitrate, with and without sulphuric acid and sodium sulphate. Five years of treatment, at canopy height, with up to 100 kg N and S ha-1y-1 were extended for a further 3 years, for half the plots, while the remaining plots were deprived of N, sulphuric acid or S. Stem area increment was unresponsive, whereas foliar N and Mg concentrations and fine roots were sensitive to the removal of N and acidity. This recovery experiment confirmed that the presence of acidified S modifies the fate of N and suggests the reduction in acidified S deposition will increase the bioavailability of N.