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- Boeckx, Pascal, et al.
(författare)
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LEAKY NITROGEN CYCLE IN PRISTINE AFRICAN MOUNTAIN FOREST
- 2014
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Ingår i: Biogeomon 2014. 8th International Symposium on Ecosystem Behavior, July 13th – 17th, 2014, University of Bayreuth, Germany.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Groenigen, Jan W. van, et al.
(författare)
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The soil N cycle: new insights and key challenges
- 2015
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Ingår i: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 1:1, s. 235-256
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Tidskriftsartikel (refereegranskat)abstract
- The study of soil N cycling processes has been, is, and will be at the centre of attention in soil science research. The importance of N as a nutrient for all biota; the ever-increasing rates of its anthropogenic input in terrestrial (agro)ecosystems; its resultant losses to the environment; and the complexity of the biological, physical, and chemical factors that regulate N cycling processes all contribute to the necessity of further understanding, measuring, and altering the soil N cycle. Here, we review important insights with respect to the soil N cycle that have been made over the last decade, and present a personal view on the key challenges of future research. We identify three key challenges with respect to basic N cycling processes producing gaseous emissions: 1. quantifying the importance of nitrifier denitrification and its main controlling factors; 2. characterizing the greenhouse gas mitigation potential and microbiological basis for N2O consumption; 3. characterizing hotspots and hot moments of denitrification Furthermore, we identified a key challenge with respect to modelling: 1. disentangling gross N transformation rates using advanced 15N / 18O tracing models Finally, we propose four key challenges related to how ecological interactions control N cycling processes: 1. linking functional diversity of soil fauna to N cycling processes beyond mineralization; 2. determining the functional relationship between root traits and soil N cycling; 3. characterizing the control that different types of mycorrhizal symbioses exert on N cycling; 4. quantifying the contribution of non-symbiotic pathways to total N fixation fluxes in natural systems We postulate that addressing these challenges will constitute a comprehensive research agenda with respect to the N cycle for the next decade. Such an agenda would help us to meet future challenges on food and energy security, biodiversity conservation, water and air quality, and climate stability.
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| 4. |
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| 5. |
- Nelissen, Victoria, et al.
(författare)
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Temporal evolution of biochar’s impact on soil nitrogen processes - a 15N tracing study
- 2015
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Ingår i: Global Change Biology Bioenergy. - : Wiley. - 1757-1693 .- 1757-1707. ; 7:4, s. 635-645
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Tidskriftsartikel (refereegranskat)abstract
- Biochar addition to soils has been proposed as a means to increase soil fertility and carbon sequestration. However, its effect on soil nitrogen (N) cycling and N availability is poorly understood. To gain better insight into the temporal variability of the impact of biochar on gross soil N dynamics, two 15N tracing experiments, in combination with numerical data analysis, were conducted with soil from a biochar field trial, 1 day and 1 year after application of a woody biochar type. The results showed accelerated soil N cycling immediately following biochar addition, with increased gross N mineralization (+34%), nitrification (+13%) and ammonium (NH4+) and nitrate (NO3−) immobilization rates (+4500% and +511%, respectively). One year after biochar application, the biochar acted as an inert substance with respect to N cycling. In the short term, biochar's labile C fraction and a pH increase can explain stimulated microbial activity, while in the longer term, when the labile C fraction has been mineralized and the pH effect has faded, the accelerating effect of biochar on N cycling ceases. In conclusion, biochar accelerates soil N transformations in the short-term through stimulating soil microbial activity, thereby increasing N bio-availability. This effect is, however, temporary.
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| 8. |
- Rütting, Tobias, 1977, et al.
(författare)
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Functional role of DNRA and nitrite reduction in a pristine south Chilean Nothofagus forest
- 2008
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Ingår i: Biogeochemistry. ; 90:3, s. 243-258
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Tidskriftsartikel (refereegranskat)abstract
- Nitrite (NO2 −) is an intermediate in a variety of soil N cycling processes. However, NO2 − dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3 −, NH4 + and NO2 −. Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of functional links between (1) NH4 + oxidation, the main process for NO2 − production (nitritation), and NO2 − reduction, and (2) oxidation of soil organic N, the dominant NO3 − production process in this soil, and dissimilatory NO3 − reduction to NH4 + (DNRA). The production of NH4 + via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the rate of DNRA was several magnitudes higher than the rate of other NO3 − reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic conditions of this Nothofagus ecosystem.
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| 9. |
- Rütting, Tobias, 1977, et al.
(författare)
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Increased fungal dominance in N2O emission hotspots along a natural pH gradient in organic forest soil
- 2013
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 49:6, s. 715-721
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Tidskriftsartikel (refereegranskat)abstract
- Drained organic forest soils represent a hotspot for nitrous oxide (N2O) emissions, which are directly related to soil fertility, with generally higher emissions from N-rich soils. Highest N2O emissions have been observed in organic forest soils with low pH. The mechanisms for these high emissions are not fully understood. Therefore, the present study was conducted to gain a deeper insight into the underlying mechanisms that drive high N2O emissions from acid soils. Specifically, we investigated the microbial community structure, by phospholipid fatty acid analysis, along a natural pH gradient in an organic forest soil combined with measurements of physico-chemical soil properties. These were then statistically related to site-specific estimates of annual N2O emissions along the same natural pH gradient. Our results indicate that acidic locations with high N2O emissions had a microbial community with an increased fungal dominance. This finding points to the importance of fungi for N2O emissions from acid soils. This may either be directly via fungal N2O production or indirectly via the effect of fungi on the N2O production by other microorganisms (nitrifiers and denitrifiers). The latter may be due to fungal mediated N mineralization, providing substrate for N2O production, or by creating favourable conditions for the bacterial denitrifier community. Therefore, we conclude that enhanced N2O emission from acid forest soil is related, in addition to the known inhibitory effect of low pH on bacterial N2O reduction, to a soil microbial community with increased fungal dominance. Further studies are needed to reveal the exact mechanisms.
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| 10. |
- 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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