| 1. |
- Kehoe, Laura, et al.
(author)
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Make EU trade with Brazil sustainable
- 2019
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Journal article (other academic/artistic)
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| 2. |
- 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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| 3. |
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| 4. |
- Andresen, Louise C., 1974, et al.
(author)
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Depolymerization and mineralization – investigating N availability by a novel 15N tracing model
- 2016
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In: SOIL. - : Copernicus GmbH. - 2199-398X. ; 2:3, s. 433-442
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Journal article (other academic/artistic)abstract
- Depolymerization of soil organic matter such as proteins and peptides into monomers (e.g. amino acids) is currently thought to be the rate limiting step for N availability in terrestrial N cycles. The mineralization of free amino acids (FAA), liberated by depolymerization of peptides, is an important fraction of the total N mineralization. Accurate assessment 10 of peptide depolymerization and FAA mineralization rates is important in order to gain a better understanding of the N cycle dynamics. Due to the short time span, soil disturbance and unnatural high FAA content during the first few hours after the labelling with the traditional 15N pool dilution experiments, analytical models might overestimate peptide depolymerization rate. In this paper, we present an extended numerical 15N tracing model Ntrace which incorporates the FAA pool and related N processes in order to 1) provide a more robust and coherent estimation of production and mineralization rates of FAAs; 2) 15 and 2) suggest an amino acid N use efficiency (NUEFAA) for soil microbes, which is a more realistic estimation of soil microbial NUE compared to the NUE estimated by analytical methods. We compare analytical and numerical approaches for two forest soils; suggest improvements of the experimental work for future studies; and conclude that: i) FAA mineralization might be as equally an important rate limiting step for gross N mineralization as peptide depolymerization rate is, because about half of all depolymerized peptide N is consecutively being mineralized; and that ii) FAA mineralization and FAA 20 immobilization rates should be used for assessing NUEFAA.
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| 5. |
- 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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| 6. |
- Andresen, Louise C., 1974, et al.
(author)
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Nitrogen dynamics after two years of elevated CO2 in phosphorus limited Eucalyptus woodland
- 2020
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In: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 150, s. 297-312
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Journal article (peer-reviewed)abstract
- It is uncertain how the predicted further rise of atmospheric carbon dioxide (CO2) concentration will affect plant nutrient availability in the future through indirect effects on the gross rates of nitrogen (N) mineralization (production of ammonium) and depolymerization (production of free amino acids) in soil. The response of soil nutrient availability to increasing atmospheric CO2 is particularly important for nutrient poor ecosystems. Within a FACE (Free-Air Carbon dioxide Enrichment) experiment in a native, nutrient poor Eucalyptus woodland (EucFACE) with low soil organic matter (≤ 3%), our results suggested there was no shortage of N. Despite this, microbial N use efficiency was high (c. 90%). The free amino acid (FAA) pool had a fast turnover time (4 h) compared to that of ammonium (NH4+) which was 11 h. Both NH4-N and FAA-N were important N pools; however, protein depolymerization rate was three times faster than gross N mineralization rates, indicating that organic N is directly important in the internal ecosystem N cycle. Hence, the depolymerization was the major provider of plant available N, while the gross N mineralization rate was the constraining factor for inorganic N. After two years of elevated CO2, no major effects on the pools and rates of the soil N cycle were found in spring (November) or at the end of summer (March). The limited response of N pools or N transformation rates to elevated CO2 suggest that N availability was not the limiting factor behind the lack of plant growth response to elevated CO2, previously observed at the site.
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| 7. |
- Andresen, Louise C., 1974, et al.
(author)
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Patterns of free amino acids in tundra soils reflect mycorrhizal type, shrubification, and warming
- 2022
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In: Mycorrhiza. - : Springer Science and Business Media LLC. - 0940-6360 .- 1432-1890. ; 32:3-4, s. 305-313
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Journal article (peer-reviewed)abstract
- The soil nitrogen (N) cycle in cold terrestrial ecosystems is slow and organically bound N is an important source of N for plants in these ecosystems. Many plant species can take up free amino acids from these infertile soils, either directly or indirectly via their mycorrhizal fungi. We hypothesized that plant community changes and local plant community differences will alter the soil free amino acid pool and composition; and that long-term warming could enhance this effect. To test this, we studied the composition of extractable free amino acids at five separate heath, meadow, and bog locations in subarctic and alpine Scandinavia, with long-term (13 to 24 years) warming manipulations. The plant communities all included a mixture of ecto-, ericoid-, and arbuscular mycorrhizal plant species. Vegetation dominated by grasses and forbs with arbuscular and non-mycorrhizal associations showed highest soil free amino acid content, distinguishing them from the sites dominated by shrubs with ecto- and ericoid-mycorrhizal associations. Warming increased shrub and decreased moss cover at two sites, and by using redundancy analysis, we found that altered soil free amino acid composition was related to this plant cover change. From this, we conclude that the mycorrhizal type is important in controlling soil N cycling and that expansion of shrubs with ectomycorrhiza (and to some extent ericoid mycorrhiza) can help retain N within the ecosystems by tightening the N cycle.
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| 8. |
- Andresen, Louise C., 1974, et al.
(author)
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Simultaneous quantification of depolymerization and mineralization rates by a novel 15N tracing model
- 2016
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In: SOIL. - : Copernicus GmbH. - 2199-398X. ; 2, s. 433-442
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Journal article (peer-reviewed)abstract
- The depolymerization of soil organic matter, such as proteins and (oligo-)peptides, into monomers (e.g. amino acids) is currently considered to be the rate-limiting step for nitrogen (N) availability in terrestrial ecosystems. The mineralization of free amino acids (FAAs), liberated by the depolymerization of peptides, is an important fraction of the total mineralization of organic N. Hence, the accurate assessment of peptide depoly- merization and FAA mineralization rates is important in order to gain a better process-based understanding of the soil N cycle. In this paper, we present an extended numerical 15 N tracing model Ntrace , which incorporates the FAA pool and related N processes in order to provide a more robust and simultaneous quantification of de- polymerization and gross mineralization rates of FAAs and soil organic N. We discuss analytical and numerical approaches for two forest soils, suggest improvements of the experimental work for future studies, and conclude that (i) when about half of all depolymerized peptide N is directly mineralized, FAA mineralization can be as important a rate-limiting step for total gross N mineralization as peptide depolymerization rate; (ii) gross FAA mineralization and FAA immobilization rates can be used to develop FAA use efficiency (NUEFAA), which can reveal microbial N or carbon (C) limitation.
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| 9. |
- Aurangojeb, Mohammad, et al.
(author)
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Nitrous oxide emissions from Norway spruce forests on drained organic and mineral soil
- 2017
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In: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 47:11, s. 1482-1487
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Journal article (peer-reviewed)abstract
- Nitrous oxide (N2O) emissions from drained organic (Histosol) and mineral (Umbrisol) soils having a 60 year old Norway spruce (Picea abies (L.) Karst.) forest in a catchment in southwest Sweden were measured using static closed chambers every other week over 3 years (August 2010 - July 2013). High emissions were observed during the summer months for both sites, which were significantly higher for the drained organic soils compared to the mineral soils: average emissions of 49.0 +/- 3.3 and 8.0 +/- 3.3 mu g N2O.m(-2).h(-1), respectively. As the experiment was designed to have similar forest and weather conditions for both sites, these were omitted as explanatory factors for the emission difference. Initially, the soil organic matter concentration (percent by mass) difference was thought to be the cause. However, the results found that the soil organic matter amount per square metre of top soil was similar at both sites, suggesting other possible explanations. We propose that the most plausible explanation is that higher tree growth and mycorrhizal nitrogen demand reduce nitrogen availability contributing to the lower N2O emissions from the mineral soil site.
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| 10. |
- 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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