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- Forsmark, Benjamin, et al.
(författare)
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Low and High Nitrogen Deposition Rates in Northern Coniferous Forests Have Different Impacts on Aboveground Litter Production, Soil Respiration, and Soil Carbon Stocks
- 2020
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 23, s. 1423-1436
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) deposition can change the carbon (C) sink of northern coniferous forests by changing the balance between net primary production and soil respiration. We used a field experiment in an N poor Pinus sylvestris forest where five levels of N (0, 3, 6, 12, and 50 kg N ha−1 yr−1, n = 6) had been added annually for 12–13 years to investigate how litter C inputs and soil respiration, divided into its autotrophic and heterotrophic sources, respond to different rates of N input, and its subsequent effect on soil C storage. The highest N addition rate (50 kg N ha−1 yr−1) stimulated soil C accumulation in the organic layer by 22.3 kg C kg−1 N added, increased litter inputs by 46%, and decreased soil respiration per mass unit of soil C by 31.2%, mainly by decreasing autotrophic respiration. Lower N addition rates (≤ 12 kg N ha−1 yr−1) had no effect on litter inputs or soil respiration. These results support previous studies reporting on increased litter inputs coupled to impeded soil C mineralization, contributing to enhancing the soil C sink when N is supplied at high rates, but add observations for lower N addition rates more realistic for N deposition. In doing so, we show that litter production in N poor northern coniferous forests can be relatively unresponsive to low N deposition levels, that stimulation of microbial activity at low N additions is unlikely to reduce the soil C sink, and that high levels of N deposition enhance the soil C sink by increasing litter inputs and decreasing soil respiration.
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| 2. |
- Nordin, Annika, et al.
(författare)
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Complex Biotic Interactions Drive Long-Term Vegetation Change in a Nitrogen Enriched Boreal Forest
- 2009
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 12, s. 1204-1211
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Tidskriftsartikel (refereegranskat)abstract
- The effects of experimental nitrogen (N) additions (0, 12.5, and 50 kg N ha(-1) y(-1)) on long-term (12 years) understorey vegetation dynamics were examined in a boreal forest. The results showed that two types of natural enemies of the dominant dwarf-shrub Vaccinium myrtillus (pathogenic fungus of the species Valdensia heterodoxa and herbivorous larvae of the genus Operophtera) influenced the vegetation dynamics. The pathogenic fungus, causing premature leaf-shed of V. myrtillus, showed a strong positive N response during the initial 5-year period. For the larvae, a relatively modest N response was overshadowed by an almost 40-fold population increase during an outbreak event that followed the initial 5-year period. This outbreak occurred irrespective of N addition, resulting in V. myrtillus decline and depriving the pathogenic fungus of its substrate. Hence our study demonstrates that vegetation dynamics in this relatively species poor and seemingly simple ecosystem are driven by complex biotic interactions. Further, we show that an important component of these interactions is the temporal alternation of the two natural enemies and, resultant regulation of the dominant plant's abundance. Finally, we emphasize that long-term data are essential to capture the complexity of this type of biotic interactions. In our case, a short-term study may have resulted in markedly different conclusions regarding effects of N enrichment and the role of biotic interactions for forest vegetation dynamics.
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