Nitrogen addition and removal at Gårdsjön — effects on fine-root growth and fine-root chemistry

Abstract

Investigations were carried out on Norway spruce ( Picea abies) fine-root growth in 3 catchment areas subjected to decreased nitrogen (N) and sulphur (S) deposition (G1 ROOF), increased N deposition (G2 NITREX) and ambient levels of N and S deposition (F1 CONTROL), within the Lake Gårdsjön basin, SW Sweden. Root sampling was performed using ingrowth cores which were installed and resampled in 2-year intervals at the 3 catchments. The amount of fine roots in the resampled ingrowth cores was interpreted as a direct measure of tree vitality. There was a gradual decline in fine-root growth in the F1 CONTROL catchment from 1991 onwards; whereas, reduced N and S deposition in the G1 ROOF resulted in a tendency towards stabilisation and a gradual recovery. This stabilisation process was also indicated by better nutritional conditions in the fine roots, viz. increased potassium (K), phosphorous (P) and calcium (Ca) levels in relation to N. The K level did not change at F1 CONTROL, and stayed at a low level relative to N. The G2 NITREX exposed to increased N exhibited a tendency towards decline, but not as consistent as for the F1 CONTROL. Increase of K, P and Ca levels relative to N in G1 NITREX occurred probably as a result of ion exchange caused by the added ammonium nitrate. Considerable differences were observed in ingrowth rates between different growth periods, in particular at F1 CONTROL and G2 NITREX.