| 1. |
- Lembrechts, Jonas J., et al.
(author)
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Global maps of soil temperature
- 2022
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:9, s. 3110-3144
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Journal article (peer-reviewed)abstract
- Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.
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| 2. |
- Groenigen, Jan W. van, et al.
(author)
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The soil N cycle: new insights and key challenges
- 2015
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In: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 1:1, s. 235-256
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Journal article (peer-reviewed)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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| 3. |
- Bauters, Marijn, et al.
(author)
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Contrasting nitrogen fluxes in African tropical forests of the Congo Basin
- 2019
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In: Ecological Monographs. - : Wiley. - 0012-9615 .- 1557-7015. ; 89:1
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Journal article (peer-reviewed)abstract
- The observation of high losses of bioavailable nitrogen (N) and N richness in tropical forests is paradoxical with an apparent lack of N input. Hence, the current concept asserts that biological nitrogen fixation (BNF) must be a major N input for tropical forests. However, well-characterized N cycles are rare and geographically biased; organic N compounds are often neglected and soil gross N cycling is not well quantified. We conducted comprehensive N input and output measurements in four tropical forest types of the Congo Basin with contrasting biotic (mycorrhizal association) and abiotic (lowland–highland) environments. In 12 standardized setups, we monitored N deposition, throughfall, litterfall, leaching, and export during one hydrological year and completed this empirical N budget with nitrous oxide (N2O) flux measurement campaigns in both wet and dry season and in situ gross soil N transformations using 15N-tracing and numerical modeling. We found that all forests showed a very tight soil N cycle, with gross mineralization to immobilization ratios (M/I) close to 1 and relatively low gross nitrification to mineralization ratios (N/M). This was in line with the observation of dissolved organic nitrogen (DON) dominating N losses for the most abundant, arbuscular mycorrhizal associated, lowland forest type, but in contrast with high losses of dissolved inorganic nitrogen (DIN) in all other forest types. Altogether, our observations show that different forest types in central Africa exhibit N fluxes of contrasting magnitudes and N-species composition. In contrast to many Neotropical forests, our estimated N budgets of central African forests are imbalanced by a higher N input than output, with organic N contributing significantly to the input-output balance. This suggests that important other losses that are unaccounted for (e.g., NOx and N2 as well as particulate N) might play a major role in the N cycle of mature African tropical forests.
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| 4. |
- Rütting, Tobias, 1977, et al.
(author)
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New insights on N transformations by 15N tracing techniques
- 2009
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In: Working Papers of the Finnish Forest Research Institute. - 1795-150X. - 9789514021763 ; 128
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Conference paper (peer-reviewed)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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| 5. |
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| 6. |
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| 7. |
- Staelens, Jeroen, et al.
(author)
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Nitrogen dynamics in contrasting forest ecosystems exposed to enhanced atmospheric N deposition
- 2009
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In: Working Papers of the Finnish Forest Research Institute. - 1795-150X. - 9789514021763 ; 128
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Conference paper (peer-reviewed)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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| 8. |
- Nelissen, Victoria, et al.
(author)
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Temporal evolution of biochar’s impact on soil nitrogen processes - a 15N tracing study
- 2015
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In: Global Change Biology Bioenergy. - : Wiley. - 1757-1693 .- 1757-1707. ; 7:4
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Journal article (peer-reviewed)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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| 9. |
- Andresen, Louise C., 1974, et al.
(author)
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Amino acid and N mineralization dynamics in heathland soil after long-term warming and repetitive drought
- 2015
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In: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 1:1, s. 341-349
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Journal article (peer-reviewed)abstract
- Monomeric organic nitrogen (N) compounds such as free amino acids (FAAs) are an important resource for both plants and soil microorganisms and a source of ammonium (NH4+) via microbial FAA mineralization. We compared gross FAA dynamics with gross N mineralization in a Dutch heathland soil using a 15N tracing technique. A special focus was made on the effects of climate change factors warming and drought, followed by rewetting. Our aims were to (1) compare FAA mineralization (NH4+ production from FAAs) with gross N mineralization, (2) assess gross FAA production rate (depolymerization) and turnover time relative to gross N mineralization rate, and (3) assess the effects of a 14 years of warming and drought treatment on these rates. The turnover of FAA in the soil was ca. 3 h, which is almost 2 orders of magnitude faster than that of NH4+ (i.e. ca. 4 days). This suggests that FAA is an extensively used resource by soil microorganisms. In control soil (i.e. no climatic treatment), the gross N mineralization rate (10 ± 2.9 μg N g−1 day−1) was 8 times smaller than the total gross FAA production rate of five AAs (alanine, valine, leucine, isoleucine, proline: 127.4 to 25.0 μg N g−1 day−1). Gross FAA mineralization (3.4 ± 0.2 μg N g−1 day−1) contributed 34% to the gross N mineralization rate and is therefore an important component of N mineralization. In the drought treatment, a 6–29% reduction in annual precipitation caused a decrease of gross FAA production by 65% and of gross FAA mineralization by 41% compared to control. On the other hand, gross N mineralization was unaffected by drought, indicating an increased mineralization of other soil organic nitrogen (SON) components. A 0.5–1.5 °C warming did not significantly affect N transformations, even though gross FAA production declined. Overall our results suggest that in heathland soil exposed to droughts a different type of SON pool is mineralized. Furthermore, compared to agricultural soils, FAA mineralization was relatively less important in the investigated heathland. This indicates more complex mineralization dynamics in semi-natural ecosystems.
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| 10. |
- Andresen, Louise C., 1974, et al.
(author)
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Free amino acids in the rhizosphere
- 2014
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In: 19th European Nitrogen Cycle Meeting. September 10-12th 2014, Gent, Belgium.
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Conference paper (other academic/artistic)
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