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- Rütting, Tobias, 1977, et al.
(författare)
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New insights on N transformations by 15N tracing techniques
- 2009
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Ingår i: Working Papers of the Finnish Forest Research Institute. - 1795-150X. - 9789514021763 ; 128
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Konferensbidrag (refereegranskat)abstract
- In recent years the understanding of the nitrogen (N) cycling in soil experienced great changes due to the discovery of a variety of new processes or underpinning the importance of alternative processes, including anaerobic ammonium oxidation (anammox), archaeal nitrification, fungal denitrification and co-denitrification, heterotrophic nitrification and nitrifier denitrification (Francis et al., 2007; Hayatsu et al., 2008). A widely used method to investigate N cycling are 15N tracing studies where one or more soil N pools are labelled with 15N and subsequently the concentrations and 15N enrichments are followed over a period of time. The main objective of these studies is to quantify the simultaneously occurring gross N transformations. Recent progress in 15N tracing models (Müller et al., 2007) enables us to perform more comprehensive process-specific analyses of the N cycle and investigate the ecological importance of previously ignored processes such as heterotrophic nitrification and dissimilatory nitrate reduction to ammonium (DNRA) (Rütting et al., 2008). Here we present results from several 15N labelling studies in temperate grassland and forest ecosystems from the northern and southern hemisphere. In these ecosystems DNRA is the dominant, sometimes exclusive pathway of NO3- consumption. The main advantage of DNRA over other NO3- consumption processes is that N is transferred into NH4+, another plant available N form, which is not prone to N losses. Therefore DNRA leads to conservation of mineral N in soils.
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| 2. |
- Staelens, Jeroen, et al.
(författare)
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Nitrogen dynamics in contrasting forest ecosystems exposed to enhanced atmospheric N deposition
- 2009
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Ingår i: Working Papers of the Finnish Forest Research Institute. - 1795-150X. - 9789514021763 ; 128
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Konferensbidrag (refereegranskat)abstract
- Despite chronically enhanced nitrogen (N) deposition to forest ecosystems in Europe and NE America, considerable N retention by forests has been observed. It is still unclear which factors determine N retention in forest soils. However, this knowledge is crucial to assess the impact of changing anthropogenic N emissions on future N cycling and N loss of forests. For coniferous and deciduous forest stands at comparable sites, it is known that both N deposition to the forest floor as well as N loss by leaching below the rooting zone are significantly higher in coniferous stands (De Schrijver et al., 2007). In addition, the N loss in coniferous stands is often more enhanced than can be explained by the higher N input only, which suggests lower N retention by coniferous stands and may be related to differences in litter quality, microbial activity, and N uptake by plant roots. To test this hypothesis, we studied the effect of forest type on N retention. N dynamics were examined for two adjacent forest stands (pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylvestris L.)) on a well-drained soil type and with a similar stand history, which are located in a region with high N deposition (Belgium). Firstly, input-output N budgets were established by quantifying atmospheric deposition and leaching, which confirmed the above finding of higher N deposition and disproportionately higher N loss by the pine stand than the oak stand. Secondly, the fate of inorganic N within the ecosystems was studied by spraying dissolved 15N onto the forest floor, both as ammonium (NH4+) and nitrate (NO3-). The 15N recovery over time in organic and mineral soil layers, tree roots, water leaching, ferns, foliage, and stem wood was compared between the two forest stands and N treatments. Thirdly, in situ gross N transformation rates in undisturbed mineral forest soils were determined via a 15N tracing approach (Müller et al., 2007). Meaningful differences between the two forest stands were found for the rates of mineralisation, heterotrophic and autotrophic nitrification, and NH4+ and NO3- immobilisation. Unexpectedly, dissimilatory NO3- reduction to NH4+ (DNRA) was detected in the oak soil. This process has mainly been described for unpolluted soils (e.g., Huygens et al., 2008), and to the best of our knowledge, this is the first report of DNRA under field conditions in a temperate forest soil under high N deposition.
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| 9. |
- Westberg, Lotten, et al.
(författare)
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Peer-to-peer learning experiences in Sweden
- 2011
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Ingår i: Working Paper of the Finnish Forest Research Institute. - 1795-150X. ; , s. 55-64
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper reports the results of an investigation on peer-to-peer learning experiences among small scale forest owners in Sweden. The Swedish study circle as a specific instance of peer-to-peer learning in operation was examined through an observation and interview study of a group of forest owners taking part in an ongoing study circle. The quality of peer-to-peer learning offered by the study circle network was discussed through the lens of the three dimensions of communities of practice, mutual engagement, joint enterprise and shared repertoire. Swedish study circles appear to be a promising and time tested model of peer-to-peer learning. It appears worthwhile to envision peer-to-peer learning platforms not simply as social networks to be exploited for knowledge sharing and learning gains but as opportunities for some of them to graduate into becoming active communities of practice. The paper concludes that a more comprehensive investigation might give insights into the opportunities of peer-to-peer learning in the forestry extension sector in the Nordic region.
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