Vitality fertilization of Scots pine stands growing along a gradient of heavy metal pollution: short-term effects on microbial biomass and respiration rate of the humus layer.

In 1992 forest vitality fertilization experiments were established on a heavy metal deposition gradient with four treatments in three replications at distances of 0.5, 4 and 8 km from a Cu-Ni smelter in order to estimate their impact on the disturbed forest ecosystem. The increase in Cu concentration in the humus (F/H) layer of the Calluna site type Scots pine (Pinus sylvestris) stands from ca. 300 to 8000 mg kg(-1) d.m. (dry matter) along the 8 km long transect towards the smelter resulted in declining soil microbial biomass and soil respiration activity. Three independent measurements of microbial biomass: C(mic)-FE (fumigation extraction), C(mic)-SIR (substrate induced respiration), and ATP have been used together with an indicator of fungal biomass (ergosterol) and microbial activity (soil respiration). Within this Cu pollution range, all the measured microbial biomass levels declined to 10%-28% of the control plot values and activity assessed by respiration was lowered to 16%. Liming has increased the C(mic)-SIR and respiration rate. Treatments with test fertilizer, made from grounded apatite, did not result in different microbial biomass and respiration rate values compared to the respective controls along the whole gradient. Nitrogen + lime treatments resulted in similar changes to lime alone. No changes, as compared to the respective control, could be detected with nitrogen fertilization at the less polluted end of the gradient.