Fine-root response to nitrogen addition and removal at Gårdsjön — results from ingrowth cores

Abstract

Investigations were carried out in 1991-94 to determine the experimental impact on Norway spruce ( Picea abies) fine-root growth in three catchment areas subjected to decreased nitrogen and sulphur deposition (G1 ROOF), increased nitrogen deposition (G2 NITREX; addition of 50 kg N as ammonium nitrate/ha per year) and ambient levels of nitrogen and sulphur deposition (F1 CONTROL), respectively, within the Lake Gardsjon basin, SW Sweden. Root sampling was performed using ingrowth cores, which were installed and resampled in two year intervals at three catchments. There was a gradual, in most cases significant, decrease in fine-root growth in the F1 CONTROL catchment from 1991 onwards, whereas reduced nitrogen and sulphur deposition in the G1 ROOF resulted in a tendency towards stabilisation and a gradual recovery. The G2 NITREX exposed to increased nitrogen and sulphur also exhibited a tendency towards decrease, but not as consistent as for the F1 CONTROL. A similar ingrowth pattern was shown in both Vaccinium myrtillus and Dicranum-dominated parts of all catchments. Considerable differences in the two year ingrowth pattern were found in all catchments except for the G1 ROOF.