MICROBIAL BIOMASS C AND N, AND RESPIRATORY ACTIVITY IN SOIL OF REPEATEDLY LIMED AND N-FERTILIZED AND P-FERTILIZED NORWAY SPRUCE STANDS

Our aim was to assess long-term effects of repeated liming and N and P additions on soil microbial biomass and activity. The experimental sites were four, 40-60 yr old, Norway spruce (Picea abies L.) stands growing on mineral soil sites. During the 30 yr study period, the cumulative amount of finely-ground limestone totalled 6000 kg ha-1, and fertilizer N and P totalled 530-950 and 70-115 kg ha-1, respectively. The main effects of the additions, expressed on an organic matter basis, were as follows: liming increased, and N addition decreased, both the fumigation-extraction (FE) and substrate-induced-respiration (SIR) derived microbial biomass C, microbial biomass N and its proportion of total soil N, and microbial respiration rate. Nitrogen addition increased slightly the soil ergosterol content, indicating an increase in fungal biomass or a change in fungal population structure. There were no significant differences in microbial C:N ratio and respiration: biomass ratio between the treatments. No clear effects of P addition were observed.