Abstract
We have reviewed information on early-, late- and limit-value decomposition stages for litter of Norway spruce (Picea abies) and Scots pine (Pinus silvestris). This synthesis covers c 16 studies/papers made along a climatic gradient; range in mean annual temperature (MAT) from −1 to +7 °C and mean annual precipitation (MAP) from 425 to 1070 mm. Scots pine has an early stage dominated by carbohydrate decomposition and a late stage dominated by decomposition of lignin; Norway spruce has just one stage dominated by lignin decomposition. We used data for annual mass loss to identify rate-regulating factors in both stages; climate data, namely, MAT and MAP, as well as substrate properties, namely, nitrogen (N), acid unhydrolyzable residue (AUR), manganese (Mn). Early-stage decomposition for Scots pine litter was dominated positively by MAT; the late stage was dominated negatively by MAT, N, and AUR, changing with decomposition stage; there was no effect of Mn. Norway spruce litter had no early stage; decomposition in the lignin-dominated stage was mainly negative to MAP, a negative relationship to AUR and non-significant relationships to N and MAT. Mn had a positive relationship. Limit values for decomposition, namely, the accumulated mass loss at which decomposition is calculated to be zero, were related positively to Mn and AUR for Scots pine litter and negatively to AUR for Norway spruce litter. With different sets of rate-regulating factors as well as different compounds/elements related to the limit values, the decomposition patterns or pathways are different.
Highlights
Climate has a dominant effect on litter decomposition rates on a regional scale, whereas litter quality dominates on a local level [1]
The initial concentration ranges for elements and acid unhydrolyzable residue (AUR) in the data set were rather similar for Scots pine and Norway spruce litter (Table 1)
The annual mass losses were regulated by (i) differing levels of lignification creating a three-phase and a two-phase process, (ii) decomposition in the lignified phases was in part influenced by different factors such as a strong negative influence by N for Scots pine but not for Norway spruce
Summary
Climate has a dominant effect on litter decomposition rates on a regional scale, whereas litter quality dominates on a local level [1]. Berg et al [2], using newly shed Scots pine (Pinus silvestris) needle litter, confirmed that relationship for the first-year mass loss, which mainly corresponded to the early decomposition stage [3]. 30% accumulated mass loss for Scots pine litter, about 70% of the litter mass should be in a late stage and its decomposition pattern has been shown to depend on other limiting factors compared to those for the early stage [3,8] This was in part illustrated by Berg et al [9] using annual mass loss for pine species (Pinus) litter in the late stage and by Hobbie et al [10], who demonstrated the effect of hydrolytic enzymes for the decomposition of nonlignified cellulose in the early stage and that of oxidative, lignin-degrading enzymes for the lignindominated (late) stage
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