| 1. |
- Franklin, Oskar, et al.
(författare)
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Pine forest floor carbon accumulation in response to N and PK additions : Bomb C-14 modelling and respiration studies
- 2003
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 6:7, s. 644-658
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Tidskriftsartikel (refereegranskat)abstract
- The addition of nitrogen via deposition alters the carbon balance of temperate forest ecosystems by affecting both production and decomposition rates. The effects of 20 years of nitrogen (N) and phosphorus and potassium (PK) additions were studied in a 40-year-old pine stand in northern Sweden. Carbon fluxes of the forest floor were reconstructed using a combination of data on soil 14C, tree growth, and litter decomposition. N-only additions caused an increase in needle litterfall, whereas both N and PK additions reduced long-term decomposition rates. Soil respiration measurements showed a 40% reduction in soil respiration for treated compared to control plots. The average age of forest floor carbon was 17 years. Predictions of future soil carbon storage indicate an increase of around 100% in the next 100 years for the N plots and 200% for the NPK plots. As much as 70% of the increase in soil carbon was attributed to the decreased decomposition rate, whereas only 20% was attributable to increased litter production. A reduction in decomposition was observed at a rate of N addition of 30 kg C ha−1 y−1, which is not an uncommon rate of N deposition in central Europe. A model based on the continuous-quality decomposition theory was applied to interpret decomposer and substrate parameters. The most likely explanations for the decreased decomposition rate were a fertilizer-induced increase in decomposer efficiency (production-to-assimilation ratio), a more rapid rate of decrease in litter quality, and a decrease in decomposer basic growth rate.
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| 2. |
- Ladanai, Svetlana, et al.
(författare)
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Relationships Between Tree and Soil Properties in Picea abies and Pinus sylvestris Forests in Sweden
- 2010
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 13, s. 302-316
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Tidskriftsartikel (refereegranskat)abstract
- The exchange of elements between plants and the soil in which they are growing creates reciprocal control of their element composition. Within plants, the growth rate hypothesis from ecological stoichiometry implies a strong coupling between C, N, and P. No similar theory exists for predicting relationships between elements in the soil or relationships between plants and the soil. We used a data set of element concentrations in needles and humus of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) forests in Sweden to investigate the extent to which relationships between elements (C, N, P, S, K, Ca, Mg, Fe, Mn, Al) can be observed within and between plants and soils. We found element composition to be more strongly controlled in needles than in humus. Elements that are covalently bound were also more strongly controlled, with no apparent differences between macro- and micronutrients. With the exception of N/C, there were surprisingly few relationships between elements in needles and humus. We found no major differences between the two tree species studied, but investigations of additional forest types are needed for firm conclusions. More control over element composition was exercised with respect to N than C, particularly in needles, so it might be advantageous to express nutrient concentrations relative to N rather than on a dry weight or carbon basis. Variations in many ecosystem variables appeared to lack ecological significance and thus an important task is to identify the meaningful predictors.
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| 3. |
- Ågren, Göran, et al.
(författare)
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Ectomycorrhiza, Friend or Foe?
- 2019
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 22, s. 1561-1572
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Tidskriftsartikel (refereegranskat)abstract
- Many ecology textbooks present the interaction between mycorrhizal fungi and their host plants as the archetype of symbiosis or mutualism. However, mycorrhiza drains carbon directly from the plant and also competes with the plant for soil inorganic nitrogen. We developed hypotheses based on a simple model to qualitatively investigate when, in a nitrogen-limited system, the fungal partner returns sufficient extra nitrogen to compensate for the amount of carbon allocated to it by the plant. We showed when the mycorrhizal association can be beneficial to the plant, but also when mycorrhizal immobilization of soil inorganic nitrogen can be a limitation. The amount of carbon and nitrogen that the mycorrhizal fungus can obtain from soil organic matter, by producing extracellular enzymes, is also important. Saprotrophic capability decreases the value of the fungus to the plant, as fungal uptake of soil carbon augments the use of the plant-supplied carbon and increases the fungal requirement for N. The stoichiometric mismatch between low-N soil organic matter and high-N fungal biochemistry turned out to be a bottleneck in making the fungus a net provider of additional N to the plant. The most important properties determining the usefulness to a plant of a mycorrhizal symbiont are plant nitrogen use efficiency and the amount of inorganic N taken up per unit extra fungal growth. The fraction of carbon the fungus allocates to its own growth, relative to its investment in exocellular enzymes, is also a critical property. Our results show that plants could benefit from the association with the fungus, which could explain the ubiquitous nature of this association between fungi and plants.
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