Does an admixture of betula species in Picea abies stands increase organic matter quality and nitrogen release?
This study examined whether organic matter quality and nitrogen (N) release are higher in mixed stands of Norway spruce ( Picea abies L. Karst.) and birch ( Betula spp.) than in pure spruce stands. The first hypothesis, that synergistic effects on carbon (C) respiration and net N mineralization occur when foliar birch and spruce litter are mixed, was tested using laboratory microcosms (453 days). The C respiration rate of mixed litter was higher (non-significantly) than average C respiration rate of pure litter, producing significantly lower C/N ratios of mixed litter after incubation. No difference was found for total net N mineralization. The second hypothesis, that potential C respiration and net N mineralization rates are higher in mixed stands than pure spruce stands, was tested by incubating samples (litter and fermentation layer, humus layer and soil) from field experiments in laboratory microcosms. Potential C respiration per unit area was higher (non-significantly) in mixed stands than in pure spruce stands, whereas potential net N mineralization was similar in both. In conclusion, organic matter quality as expressed by C respiration rates may be higher in mixed birch-spruce stands than in pure spruce stands. However, there was no evidence of differences in N release between stand types that would explain observed differences in yield.
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Document Type: Research Article
Publication date: 2004-04-01