Litter decomposition in a transect of Norway spruce forests: substrate quality and climate control

We used a climatic transect of 14 stands of Norway spruce (Picea abies (L.) Karst.) at which locally collected needle litters was incubated. Our purpose was to show that climate is not necessarily the main rate-regulating factor even in a long climatic transect. The sites are found in Sweden from 56 to 66degreesN. There was virtually no relationship between climate (AET ranging between 371 and 545 mm) and first-year mass loss (range 19.4-32.8%). Instead, substrate quality (litter Mn concentration) explained 27% of the site-to-site variation in first-year mass loss. For the later stages of decomposition (second to fifth year), the sites could be divided into two groups; one in which lignin concentration regulated litter mass-loss rates, and one in which lignin concentration was not an important control. In this latter group, Mn concentrations were the component best correlated with litter mass loss. When combining all data, Mn concentration gave the best linear relationship. We repeated this procedure using first- to fifth-year mass-loss values and found the same pattern. We concluded that litter Mn concentrations is a key factor for Norway spruce litter decomposition because of its influence on lignin degradation and that the very early stage is short or nonexistant.