Soil microbial activity in the coastal Norway spruce [Picea abies (L.) Karst.] forests of the Gulf of Bothnia in relation to humus-layer quality, moisture and soil types

Relationships between chemical, physical and microbial properties in the humus layer, soil type and crown condition of Norway spruce (Picea abies) were studied in stands located along the Finnish and Swedish coasts of the Straits of the Gulf of Bothnia. Humus layers of ferric podzols had higher basal respiration (BASAL) than those of carbic podzols and higher substrate-induced respiration (SIR) than those of both carbic podzols and dystric gleysols. BASAL and SIR correlated with environmental factors associated with humus-layer fertility; i.e. they were positively associated with pH and extractable K, Mn and P and negatively associated with organic-matter content of the humus layer. A short lag-time was associated with humus-layer fertility and a long lag-time with crown defoliation. Specific respiration increment was lowest at sites with high field moisture and discoloured crowns. The results suggest that on carbic podzols and dystric gleysols poor nutrient status, acidity and lack of oxygen due to excess moisture in the humus layer result in low microbial activity and poor condition of spruce.