| 1. |
- Adamczyk, B., et al.
(författare)
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Plant roots increase both decomposition and stable organic matter formation in boreal forest soil
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Boreal forests are ecosystems with low nitrogen (N) availability that store globally significant amounts of carbon (C), mainly in plant biomass and soil organic matter (SOM). Although crucial for future climate change predictions, the mechanisms controlling boreal C and N pools are not well understood. Here, using a three-year field experiment, we compare SOM decomposition and stabilization in the presence of roots, with exclusion of roots but presence of fungal hyphae and with exclusion of both roots and fungal hyphae. Roots accelerate SOM decomposition compared to the root exclusion treatments, but also promote a different soil N economy with higher concentrations of organic soil N compared to inorganic soil N accompanied with the build-up of stable SOM-N. In contrast, root exclusion leads to an inorganic soil N economy (i.e., high level of inorganic N) with reduced stable SOM-N buildup. Based on our findings, we provide a framework on how plant roots affect SOM decomposition and stabilization.
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| 2. |
- Blume-Werry, Gesche, 1985-, et al.
(författare)
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Arctic rooting depth distribution influences modelled carbon emissions but cannot be inferred from aboveground vegetation type
- 2023
-
Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 240:2, s. 502-514
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of roots throughout the soil drives depth-dependent plant–soil interactions and ecosystem processes, particularly in arctic tundra where plant biomass, is predominantly belowground. Vegetation is usually classified from aboveground, but it is unclear whether such classifications are suitable to estimate belowground attributes and their consequences, such as rooting depth distribution and its influence on carbon cycling. We performed a meta-analysis of 55 published arctic rooting depth profiles, testing for differences both between distributions based on aboveground vegetation types (Graminoid, Wetland, Erect-shrub, and Prostrate-shrub tundra) and between ‘Root Profile Types’ for which we defined three representative and contrasting clusters. We further analyzed potential impacts of these different rooting depth distributions on rhizosphere priming-induced carbon losses from tundra soils. Rooting depth distribution hardly differed between aboveground vegetation types but varied between Root Profile Types. Accordingly, modelled priming-induced carbon emissions were similar between aboveground vegetation types when they were applied to the entire tundra, but ranged from 7.2 to 17.6 Pg C cumulative emissions until 2100 between individual Root Profile Types. Variations in rooting depth distribution are important for the circumpolar tundra carbon-climate feedback but can currently not be inferred adequately from aboveground vegetation type classifications.
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| 3. |
- Capek, P., et al.
(författare)
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The effect of warming on the vulnerability of subducted organic carbon in arctic soils
- 2015
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 90, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- Arctic permafrost soils contain large stocks of organic carbon (OC). Extensive cryogenic processes in these soils cause subduction of a significant part of OC-rich topsoil down into mineral soil through the process of cryoturbation. Currently, one-fourth of total permafrost OC is stored in subducted organic horizons. Predicted climate change is believed to reduce the amount of OC in permafrost soils as rising temperatures will increase decomposition of OC by soil microorganisms. To estimate the sensitivity of OC decomposition to soil temperature and oxygen levels we performed a 4-month incubation experiment in which we manipulated temperature (4-20 degrees C) and oxygen level of topsoil organic, subducted organic and mineral soil horizons. Carbon loss (C-LOSS) was monitored and its potential biotic and abiotic drivers, including concentrations of available nutrients, microbial activity, biomass and stoichiometry, and extracellular oxidative and hydrolytic enzyme pools, were measured. We found that independently of the incubation temperature, C-LOSS from subducted organic and mineral soil horizons was one to two orders of magnitude lower than in the organic topsoil horizon, both under aerobic and anaerobic conditions. This corresponds to the microbial biomass being lower by one to two orders of magnitude. We argue that enzymatic degradation of autochthonous subducted OC does not provide sufficient amounts of carbon and nutrients to sustain greater microbial biomass. The resident microbial biomass relies on allochthonous fluxes of nutrients, enzymes and carbon from the OC-rich topsoil. This results in a "negative priming effect", which protects autochthonous subducted OC from decomposition at present. The vulnerability of subducted organic carbon in cryoturbated arctic soils under future climate conditions will largely depend on the amount of allochthonous carbon and nutrient fluxes from the topsoil. (C) 2015 Elsevier Ltd. All rights reserved.
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| 4. |
- Dao, Thao Thi, et al.
(författare)
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How temperature and aridity drive lignin decomposition along a latitudinal transect in western Siberia
- 2023
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Ingår i: European Journal of Soil Science. - 1351-0754 .- 1365-2389. ; 74:5
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Tidskriftsartikel (refereegranskat)abstract
- Climate change drives a northward shift of biomes in high-latitude regions. This might have consequences on the decomposition of plant litter entering the soil, including its lignin component, which is one of the most abundant components of vascular plants. In order to elucidate the combined effect of climate and soil characteristics on the decomposition pattern of lignin, we investigated lignin contents and its degree of oxidative decomposition within soil profiles along a climosequence in western Siberia. Soil samples were collected from organic topsoil to mineral subsoil at six sites along a 1500-km latitudinal transect, stretching from tundra, through taiga and forest steppe to typical steppe. The stage of lignin degradation, as mirrored by decreasing organic carbon-normalized lignin contents and increasing oxidative alteration of the remnant lignin (acid-to-aldehyde ratios of vanillyl- and syringyl-units [(Ac/Al)V and (Ac/Al)S]) within soil horizons, increased from tundra to forest steppe and then decreased to the steppe. Principal component analysis, involving also climatic conditions such as mean annual temperature and aridity index, showed that the different states of lignin degradation between horizons related well to the activity of phenoloxidases and peroxidases, enzymes involved in lignin depolymerization that are produced primarily by fungi and less importantly by bacteria. The low microbial lignin decomposition in the tundra was likely due to low temperature and high soil moisture, which do not favour the fungi. Increasing temperature and decreasing soil moisture, facilitating a higher abundance of fungi, led to increased fungal lignin decomposition towards the forest-steppe biome, while drought and high pH might be responsible for the reduced lignin decomposition in the steppe. We infer that a shift of biomes to the north, driven by climate change, might promote lignin decomposition in the northern parts, whereas in the south a further retardation might be likely.
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| 5. |
- Dao, Thao Thi, et al.
(författare)
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Lignin Preservation and Microbial Carbohydrate Metabolism in Permafrost Soils
- 2022
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 127:1
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost-affected soils in the northern circumpolar region store more than 1,000 Pg soil organic carbon (OC), and are strongly vulnerable to climatic warming. However, the extent to which changing soil environmental conditions with permafrost thaw affects different compounds of soil organic matter (OM) is poorly understood. Here, we assessed the fate of lignin and non-cellulosic carbohydrates in density fractionated soils (light fraction, LF vs. heavy fraction, HF) from three permafrost regions with decreasing continentality, expanding from east to west of northern Siberia (Cherskiy, Logata, Tazovskiy, respectively). In soils at the Tazovskiy site with thicker active layers, the LF showed smaller OC-normalized contents of lignin-derived phenols and plant-derived sugars and a decrease of these compounds with soil depth, while a constant or even increasing trend was observed in soils with shallower active layers (Cherskiy and Logata). Also in the HF, soils at the Tazovskiy site had smaller contents of OC-normalized lignin-derived phenols and plant-derived sugars along with more pronounced indicators of oxidative lignin decomposition and production of microbial-derived sugars. Active layer deepening, thus, likely favors the decomposition of lignin and plant-derived sugars, that is, lignocelluloses, by increasing water drainage and aeration. Our study suggests that climate-induced degradation of permafrost soils may promote carbon losses from lignin and associated polysaccharides by abolishing context-specific preservation mechanisms. However, relations of OC-based lignin-derived phenols and sugars in the HF with mineralogical properties suggest that future OM transformation and carbon losses will be modulated in addition by reactive soil minerals.
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| 6. |
- Demirkan, Ayse, et al.
(författare)
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Genetic architecture of circulating lipid levels
- 2011
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Ingår i: European Journal of Human Genetics. - : Springer Science and Business Media LLC. - 1018-4813 .- 1476-5438. ; 19:7, s. 813-819
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Tidskriftsartikel (refereegranskat)abstract
- Serum concentrations of low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TGs) and total cholesterol (TC) are important heritable risk factors for cardiovascular disease. Although genome-wide association studies (GWASs) of circulating lipid levels have identified numerous loci, a substantial portion of the heritability of these traits remains unexplained. Evidence of unexplained genetic variance can be detected by combining multiple independent markers into additive genetic risk scores. Such polygenic scores, constructed using results from the ENGAGE Consortium GWAS on serum lipids, were applied to predict lipid levels in an independent population-based study, the Rotterdam Study-II (RS-II). We additionally tested for evidence of a shared genetic basis for different lipid phenotypes. Finally, the polygenic score approach was used to identify an alternative genome-wide significance threshold before pathway analysis and those results were compared with those based on the classical genome-wide significance threshold. Our study provides evidence suggesting that many loci influencing circulating lipid levels remain undiscovered. Cross-prediction models suggested a small overlap between the polygenic backgrounds involved in determining LDL-C, HDL-C and TG levels. Pathway analysis utilizing the best polygenic score for TC uncovered extra information compared with using only genome-wide significant loci. These results suggest that the genetic architecture of circulating lipids involves a number of undiscovered variants with very small effects, and that increasing GWAS sample sizes will enable the identification of novel variants that regulate lipid levels.
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| 7. |
- Fuchslueger, Lucia, et al.
(författare)
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Microbial carbon and nitrogen cycling responses to drought and temperature in differently managed mountain grasslands
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 135, s. 144-153
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Tidskriftsartikel (refereegranskat)abstract
- Grassland management can modify soil microbial carbon (C) and nitrogen (N) cycling, affecting the resistance to extreme weather events, which are predicted to increase in frequency and magnitude in the near future. However, effects of grassland management on microbial C and N cycling and their responses to extreme weather events, such as droughts and heatwaves, have rarely been tested in a combined approach. We therefore investigated whether grassland management affects microbial C and N cycling responses to drought and temperature manipulation. We collected soils from in situ drought experiments conducted in an extensively managed and an abandoned mountain grassland and incubated them at two temperature levels. We measured microbial respiration and substrate incorporation, as well as gross rates of organic and inorganic N cycling to estimate microbial C and N use efficiencies (CUE and NUE). The managed grassland was characterized by lower microbial biomass, lower fungi to bacteria ratio, and higher microbial CUE, but only slightly different microbial NUE. At both sites drought induced a shift in microbial community composition driven by an increase in Gram-positive bacterial abundance. Drought significantly reduced C substrate respiration and incorporation by microbes at both sites, while microbial CUE remained constant. In contrast, drought increased gross rates of N mineralization at both sites, whereas gross amino acid uptake rates only marginally changed. We observed a significant direct, as well as interactive effect between land management and drought on microbial NUE. Increased temperatures significantly stimulated microbial respiration and reduced microbial CUE independent of drought or land management. Although microbial N processing rates showed no clear response, microbial NUE significantly decreased at higher temperatures. In summary in our study, microbial CUE, in particular respiration, is more responsive to temperature changes. Although N processing rates were stronger responding to drought than to temperature microbial NUE was affected by both drought and temperature increase. We conclude that direct effects of drought and heatwaves can induce different responses in soil microbial C and N cycling similarly in the studied land management systems.
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| 8. |
- Gentsch, N., et al.
(författare)
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Properties and bioavailability of particulate and mineral-associated organic matter in Arctic permafrost soils, Lower Kolyma Region, Russia
- 2015
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754. ; 66:4, s. 722-734
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost degradation may cause strong feedbacks of arctic ecosystems to global warming, but this will depend on if, and to what extent, organic matter (OM) is protected against biodegradation by mechanisms other than freezing and anoxia. Here, we report on the amount, chemical composition and bioavailability of particulate (POM) and mineral-associated OM (MOM) in permafrost soils of the East Siberian Arctic. The average total organic carbon (OC) stock across all soils was 24.0 +/- 6.7 kg m(-2) within 100 cm soil depth. Density fractionation (density cut-off 1.6 g cm(-3)) revealed that 54 +/- 16% of the total soil OC and 64 +/- 18% of OC in subsoil horizons was bound to minerals. As well as sorption of OM to clay-sized minerals (R-2 = 0.80; P < 0.01), co-precipitation of OM with hydrolyzable metals may also transfer carbon into the mineral-bound fraction. Carbon:nitrogen ratios, stable carbon and nitrogen isotopes, C-13-NMR and X-ray photoelectron spectroscopy showed that OM is transformed in permafrost soils, which is a prerequisite for the formation of mineral-organic associations. Mineral-associated OM in deeper soil was enriched in C-13 and N-15, and had narrow C:N and large alkyl C:(O-/N-alkyl C) ratios, indicating an advanced stage of decomposition. Despite being up to several thousands of years old, when incubated under favourable conditions (60% water-holding capacity, 15 degrees C, adequate nutrients, 90 days), only 1.5-5% of the mineral-associated OC was released as CO2. In the topsoils, POM had the largest mineralization but was even less bioavailable than the MOM in subsoil horizons. Our results suggest that the formation of mineral-organic associations acts as an important additional factor in the stabilization of OM in permafrost soils. Although the majority of MOM was not prone to decomposition under favourable conditions, mineral-organic associations host a readily accessible carbon fraction, which may actively participate in ecosystem carbon exchange.
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| 9. |
- Gentsch, N., et al.
(författare)
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Storage and transformation of organic matter fractions in cryoturbated permafrost soils across the Siberian Arctic
- 2015
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:14, s. 4525-4542
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Tidskriftsartikel (refereegranskat)abstract
- In permafrost soils, the temperature regime and the resulting cryogenic processes are important determinants of the storage of organic carbon (OC) and its small-scale spatial variability. For cryoturbated soils, there is a lack of research assessing pedon-scale heterogeneity in OC stocks and the transformation of functionally different organic matter (OM) fractions, such as particulate and mineral-associated OM. Therefore, pedons of 28 Turbels were sampled in 5m wide soil trenches across the Siberian Arctic to calculate OC and total nitrogen (TN) stocks based on digital profile mapping. Density fractionation of soil samples was performed to distinguish between particulate OM (light fraction, LF, < 1.6 g cm(-3)), mineral associated OM (heavy fraction, HF, > 1.6 g cm(-3)), and a mobilizable dissolved pool (mobilizable fraction, MoF). Across all investigated soil profiles, the total OC storage was 20.2 +/- 8.0 kgm(-2) (mean +/- SD) to 100 cm soil depth. Fifty-four percent of this OC was located in the horizons of the active layer (annual summer thawing layer), showing evidence of cryoturbation, and another 35% was present in the upper permafrost. The HF-OC dominated the overall OC stocks (55 %), followed by LF-OC (19% in mineral and 13% in organic horizons). During fractionation, approximately 13% of the OC was released as MoF, which likely represents a readily bioavailable OM pool. Cryogenic activity in combination with cold and wet conditions was the principle mechanism through which large OC stocks were sequestered in the subsoil (16.4 +/- 8.1 kgm(-2); all mineral B, C, and permafrost horizons). Approximately 22% of the subsoil OC stock can be attributed to LF material subducted by cryoturbation, whereas migration of soluble OM along freezing gradients appeared to be the principle source of the dominant HF (63 %) in the subsoil. Despite the unfavourable abiotic conditions, low C/N ratios and high delta C-13 values indicated substantial microbial OM transformation in the subsoil, but this was not reflected in altered LF and HF pool sizes. Partial least-squares regression analyses suggest that OC accumulates in the HF fraction due to co-precipitation with multivalent cations (Al, Fe) and association with poorly crystalline iron oxides and clay minerals. Our data show that, across all permafrost pedons, the mineral-associated OM represents the dominant OM fraction, suggesting that the HF-OC is the OM pool in permafrost soils on which changing soil conditions will have the largest impact.
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| 10. |
- Gentsch, Norman, et al.
(författare)
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Temperature response of permafrost soil carbon is attenuated by mineral protection
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:8, s. 3401-3415
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Tidskriftsartikel (refereegranskat)abstract
- Climate change in Arctic ecosystems fosters permafrost thaw and makes massive amounts of ancient soil organic carbon (OC) available to microbial breakdown. However, fractions of the organic matter (OM) may be protected from rapid decomposition by their association with minerals. Little is known about the effects of mineral-organic associations (MOA) on the microbial accessibility of OM in permafrost soils and it is not clear which factors control its temperature sensitivity. In order to investigate if and how permafrost soil OC turnover is affected by mineral controls, the heavy fraction (HF) representing mostly MOA was obtained by density fractionation from 27 permafrost soil profiles of the Siberian Arctic. In parallel laboratory incubations, the unfractionated soils (bulk) and their HF were comparatively incubated for 175 days at 5 and 15 degrees C. The HF was equivalent to 70 +/- 9% of the bulk CO2 respiration as compared to a share of 63 +/- 1% of bulk OC that was stored in the HF. Significant reduction of OC mineralization was found in all treatments with increasing OC content of the HF (HF-OC), clay-size minerals and Fe or Al oxyhydroxides. Temperature sensitivity (Q10) decreased with increasing soil depth from 2.4 to 1.4 in the bulk soil and from 2.9 to 1.5 in the HF. A concurrent increase in the metal-to-HF-OC ratios with soil depth suggests a stronger bonding of OM to minerals in the subsoil. There, the younger C-14 signature in CO2 than that of the OC indicates a preferential decomposition of the more recent OM and the existence of a MOA fraction with limited access of OM to decomposers. These results indicate strong mineral controls on the decomposability of OM after permafrost thaw and on its temperature sensitivity. Thus, we here provide evidence that OM temperature sensitivity can be attenuated by MOA in permafrost soils.
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| 11. |
- Keel, Sonja G., et al.
(författare)
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Allocation of carbon to fine root compounds and their residence times in a boreal forest depend on root size class and season
- 2012
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Ingår i: New Phytologist. - Malden : Wiley-Blackwell. - 0028-646X .- 1469-8137. ; 194:4, s. 972-981
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Tidskriftsartikel (refereegranskat)abstract
- Fine roots play a key role in the forest carbon balance, but their carbon dynamics remain largely unknown. We pulse labelled 50 m2 patches of young boreal forest by exposure to 13CO2 in early and late summer. Labelled photosynthates were traced into carbon compounds of < 1 and 13 mm diameter roots (fine roots), and into bulk tissue of these and first-order roots (root tips). Root tips were the most strongly labelled size class. Carbon allocation to all size classes was higher in late than in early summer; mean residence times (MRTs) in starch increased from 4 to 11 months. In structural compounds, MRTs were 0.8 yr in tips and 1.8 yr in fine roots. The MRT of carbon in sugars was in the range of days. Functional differences within the fine root population were indicated by carbon allocation patterns and residence times. Pronounced allocation of recent carbon and higher turnover rates in tips are associated with their role in nutrient and water acquisition. In fine roots, longer MRTs but high allocation to sugars and starch reflect their role in structural support and storage. Accounting for heterogeneity in carbon residence times will improve and most probably reduce the estimates of fine root production.
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| 12. |
- Keuper, Frida, et al.
(författare)
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Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming
- 2020
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 13, s. 560-565
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Tidskriftsartikel (refereegranskat)abstract
- As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism-termed the rhizosphere priming effect-may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by similar to 12%, which translates to a priming-induced absolute loss of similar to 40 Pg soil carbon from the northern permafrost area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5 degrees C.
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| 13. |
- Landhausser, S. M., et al.
(författare)
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Standardized protocols and procedures can precisely and accurately quantify non-structural carbohydrates
- 2018
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 38:12, s. 1764-1778
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Tidskriftsartikel (refereegranskat)abstract
- Non-structural carbohydrates (NSCs), the stored products of photosynthesis, building blocks for growth and fuel for respiration, are central to plant metabolism, but their measurement is challenging. Differences in methods and procedures among laboratories can cause results to vary widely, limiting our ability to integrate and generalize patterns in plant carbon balance among studies. A recent assessment found that NSC concentrations measured for a common set of samples can vary by an order of magnitude, but sources for this variability were unclear. We measured a common set of nine plant material types, and two synthetic samples with known NSC concentrations, using a common protocol for sugar extraction and starch digestion, and three different sugar quantification methods (ion chromatography, enzyme, acid) in six laboratories. We also tested how sample handling, extraction solvent and centralizing parts of the procedure in one laboratory affected results. Non-structural carbohydrate concentrations measured for synthetic samples were within about 11.5% of known values for all three methods. However, differences among quantification methods were the largest source of variation in NSC measurements for natural plant samples because the three methods quantify different NSCs. The enzyme method quantified only glucose, fructose and sucrose, with ion chromatography we additionally quantified galactose, while the acid method quantified a large range of mono- and oligosaccharides. For some natural samples, sugars quantified with the acid method were two to five times higher than with other methods, demonstrating that trees allocate carbon to a range of sugar molecules. Sample handling had little effect on measurements, while ethanol sugar extraction improved accuracy over water extraction. Our results demonstrate that reasonable accuracy of NSC measurements can be achieved when different methods are used, as long as protocols are robust and standardized. Thus, we provide detailed protocols for the extraction, digestion and quantification of NSCs in plant samples, which should improve the comparability of NSC measurements among laboratories.
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| 14. |
- Liem-Nguyen, Van, et al.
(författare)
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Spatial patterns and distributional controls of total and methylated mercury off the Lena River in the Laptev Sea sediments
- 2022
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- A warmer climate is predicted to accelerate the export of mercury (Hg) from Siberian rivers to the Arctic Ocean, yet there is a dearth of process-oriented studies on the speciation and fate of Hg in the shelf sea system. Here, we present data on total Hg (HgT) and methylmercury (MeHg) in Laptev Sea surface sediments along a cross-shelf transect starting at the mouth of the Lena River. Concentrations of HgT along the 330 km cross-shelf transect ranged within a fairly narrow span from 480 to 150 pmol g(-1) d.w., while concentrations of MeHg decreased one hundredfold from 13 pmol g(-1) d.w. near the Lena river to 0.095 pmol g(-1) d.w. in the more distall stations. The highest concentrations of HgT and MeHg were observed close to the river delta and were associated with a high supply of organic carbon (OC). Enrichment of the OC normalized HgT concentration (HgTOC) and depletion of the OC normalized MeHg concentration (MeHgOC) across the shelf suggests bulk OC content to not be the only driver of the HgT and MeHg spatial distributions. Based on correlations observed between HgTOC and MeHgOC and proxies for sediment physics and organic matter pools we suggest the spatial distribution of Hg and MeHg to also be influenced by hydrodynamic sorting of riverine-derived material. For MeHg, depletion of the MeHgOC across the shelf is likely driven by the trapping of terrestrial MeHg in sediments close to the river delta before it is degraded in the water column.
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| 15. |
- Lockhart, Erin, et al.
(författare)
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Stress-induced changes in carbon allocation among metabolite pools influence isotope-based predictions of water use efficiency in Phaseolus vulgaris
- 2016
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Ingår i: Functional Plant Biology. - 1445-4408 .- 1445-4416. ; 43:12, s. 1149-1158
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Tidskriftsartikel (refereegranskat)abstract
- Understanding how major food crops respond to environmental stress will expand our capacity to improve food production with growing populations and a changing climate. This study uses chemical and physiological adaptations to heat, water deficit and elevated light stresses in Phaseolus vulgaris L. to identify changes in carbon (C) allocation that, combined with post-photosynthetic fractionation of C isotopes, influences water use efficiency (WUE) predictions. The chemical stress response was explored through changes in C allocation to the carbohydrate and cyclitol pools using GC-triple quadrupole MS. Carbon allocation to the sucrose pool fluctuated significantly among treatments, and the putative osmolytes and osmoprotectants (myo-inositol and d-ononitol) accumulated under stress. Significant osmotic adjustment (P<0.05), quantified via pressure-volume curve analysis, was detected between control and stress treatments, although this was not attributable to active accumulation of the metabolites. Compound-specific 13C isotope abundance was measured using liquid chromatography isotope ratio MS to predict intrinsic WUE. In contrast to other metabolites measured, the δ13C of the sucrose pool fluctuated according to treatment and was proportional to predicted values based upon modelled Δ13C from gas exchange data. The results suggest that the accuracy and precision of predicting WUE may be enhanced by compound-specific analysis of Δ13C and that changes in the allocation of C among metabolite pools may influence WUE predictions based upon analysis of total soluble C. Overall, the plants appeared to use a range of mechanisms to cope with adverse conditions that could be utilised to improve plant breeding and management strategies.
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| 16. |
- Martens, Jannik, et al.
(författare)
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CASCADE - The Circum-Arctic Sediment CArbon DatabasE
- 2021
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 13:6, s. 2561-2572
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Tidskriftsartikel (refereegranskat)abstract
- Biogeochemical cycling in the semi-enclosed Arctic Ocean is strongly influenced by land-ocean transport of carbon and other elements and is vulnerable to environmental and climate changes. Sediments of the Arctic Ocean are an important part of biogeochemical cycling in the Arctic and provide the opportunity to study present and historical input and the fate of organic matter (e.g., through permafrost thawing). Comprehensive sedimentary records are required to compare differences between the Arctic regions and to study Arctic biogeochemical budgets. To this end, the Circum-Arctic Sediment CArbon DatabasE (CASCADE) was established to curate data primarily on concentrations of organic carbon (OC) and OC isotopes (delta C-13, Delta C-14) yet also on total N (TN) as well as terrigenous biomarkers and other sediment geochemical and physical properties. This new database builds on the published literature and earlier unpublished records through an extensive international community collaboration. This paper describes the establishment, structure and current status of CASCADE. The first public version includes OC concentrations in surface sediments at 4244 oceanographic stations including 2317 with TN concentrations, 1555 with delta C-13-OC values and 268 with Delta C-14-OC values and 653 records with quantified terrigenous biomarkers (high-molecular-weight n-alkanes, n-alkanoic acids and lignin phenols). CASCADE also includes data from 326 sediment cores, retrieved by shallow box or multi-coring, deep gravity/piston coring, or sea-bottom drilling. The comprehensive dataset reveals large-scale features of both OC content and OC sources between the shelf sea recipients. This offers insight into release of pre-aged terrigenous OC to the East Siberian Arctic shelf and younger terrigenous OC to the Kara Sea. Circum-Arctic sediments thereby reveal patterns of terrestrial OC remobilization and provide clues about thawing of permafrost. CASCADE enables synoptic analysis of OC in Arctic Ocean sediments and facilitates a wide array of future empirical and modeling studies of the Arctic carbon cycle. The database is openly and freely available online (https://doi.org/10.17043/cascade; Martens et al., 2021), is provided in various machine-readable data formats (data tables, GIS shapefile, GIS raster), and also provides ways for contributing data for future CASCADE versions. We will continuously update CASCADE with newly published and contributed data over the foreseeable future as part of the database management of the Bolin Centre for Climate Research at Stockholm University.
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| 17. |
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| 18. |
- Martens, Jannik, 1991-, et al.
(författare)
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Circum-Arctic release of terrestrial carbon varies between regions and sources
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Arctic change is expected to destabilize terrestrial carbon (terrOC) in soils and permafrost, leading to fluvial release, greenhouse gas emission and climate feedback. However, landscape heterogeneity and location-specific observations complicate large-scale assessments of terrOC mobilization. Here we reveal differences in terrOC release, deduced from the Circum-Arctic Sediment Carbon Database (CASCADE) using source-diagnostic (δ13C-Δ14C) and carbon accumulation data. The results show five-times larger terrOC release from the Eurasian than from the American Arctic. Most of the circum-Arctic terrOC originates from near-surface soils (61%); 30% stems from Pleistocene-age permafrost. TerrOC translocation, relative to land-based terrOC stocks, varies by a factor of five between circum-Arctic regions. Shelf seas with higher relative terrOC translocation follow the spatial pattern of recent Arctic warming, while such with lower translocation reflect long-distance lateral transport with efficient remineralization of terrOC. This study provides a receptor-based perspective for how terrOC release varies across the circum-Arctic.
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| 19. |
- Martens, Jannik, et al.
(författare)
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Remobilization of dormant carbon from Siberian-Arctic permafrost during three past warming events
- 2020
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:42
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Tidskriftsartikel (refereegranskat)abstract
- Carbon cycle models suggest that past warming events in the Arctic may have caused large-scale permafrost thaw and carbon remobilization, thus affecting atmospheric CO2 levels. However, observational records are sparse, preventing spatially extensive and time-continuous reconstructions of permafrost carbon release during the late Pleistocene and early Holocene. Using carbon isotopes and biomarkers, we demonstrate that the three most recent warming events recorded in Greenland ice cores-(i) Dansgaard-Oeschger event 3 (similar to 28 ka B.P.), (ii) Bolling-Allerod (14.7 to 12.9 ka B.P.), and (iii) early Holocene (similar to 11.7 ka B.P.)-caused massive remobilization and carbon degradation from permafrost across northeast Siberia. This amplified permafrost carbon release by one order of magnitude, particularly during the last deglaciation when global sea-level rise caused rapid flooding of the land area thereafter constituting the vast East Siberian Arctic Shelf. Demonstration of past warming-induced release of permafrost carbon provides a benchmark for the sensitivity of these large carbon pools to changing climate.
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| 20. |
- Martens, Jannik, et al.
(författare)
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Remobilization of Old Permafrost Carbon to Chukchi Sea Sediments During the End of the Last Deglaciation
- 2019
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 33:1, s. 2-14
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming is expected to destabilize permafrost carbon (PF-C) by thaw-erosion and deepening of the seasonally thawed active layer and thereby promote PF-C mineralization to CO2 and CH4. A similar PF-C remobilization might have contributed to the increase in atmospheric CO2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Delta C-14, delta C-13, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS-L2-4-PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerod warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual-carbon-isotope-based source apportionment demonstrates that Ice Complex Deposit-ice- and carbon-rich permafrost from the late Pleistocene (also referred to as Yedoma)-was the dominant source of organic carbon (66 +/- 8%; mean +/- standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 +/- 4.6 g.m(-2).year(-1)) as in the late Holocene (3.1 +/- 1.0 g.m(-2).year(-1)). These results are consistent with late deglacial PF-C remobilization observed in a Laptev Sea record, yet in contrast with PF-C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF-C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.
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| 21. |
- Martens, Jannik, 1991-
(författare)
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Remobilization of terrestrial carbon across temporal and spatial scales deduced from the Arctic Ocean sediment record
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Arctic warming is expected to trigger large-scale environmental change including remobilization of terrestrial organic carbon (terrOC). Permafrost and peatland systems contain more than twice as much carbon as the atmosphere, and may upon destabilization expose large amounts of their carbon to microbial decomposition and release climate-forcing greenhouse gases (GHG). Remobilization of terrOC also causes lateral leakage of organic matter via Arctic rivers with further translocated organic matter degradation and GHG release, while a remainder is exported to the Arctic Ocean and re-deposited in sediments. Arctic Ocean sediments are thus receptors of terrOC remobilization for a large part of the circum-Arctic drainage basin, and offer an archive to study past terrOC remobilization, e.g. during warming periods of the last deglaciation.This thesis investigates terrOC in Arctic Ocean sediments to study OC remobilization from permafrost and other terrestrial systems across temporal and spatial scales. As a first – historical – approach, permafrost OC remobilization and degradation during past warming episodes are studied using OC, dual-isotope source apportionment (13C-OC; 14C-OC) and terrestrial biomarkers (lignin phenols, long-chained n-alkanes and n-alkanoic acids) in glacial-cycle sediment cores from the Siberian continental margin. The results reveal that permafrost systems were highly vulnerable to OC release throughout past warming events, foremost during the Bølling–Allerød (14.7-12.9 kyr before present - BP) warming period and the early Holocene climate optimum (11.7-7.5 kyr BP). The sediment record shows that climate warming of about 1°C and 1.5°C (Northern Hemisphere) then triggered large-scale thawing of mostly coastal permafrost and permafrost soils in the Siberian hinterland. These results are consistent with the hypothesis that large-scale permafrost OC remobilization may have contributed to the observed rise in atmospheric CO2 during the last deglaciation, and thereby stresses the importance of permafrost thawing in the light of anthropogenic climate change. The second – spatial – study angle in this thesis investigates the contemporary Earth system and studies terrOC remobilization from permafrost and other terrestrial sources using terrOC accumulation in surface sediments of the circum-Arctic shelf seas. This includes establishment and application of the Circum-Arctic Sediment Carbon Database (CASCADE), which is a data collection of thousands of observations of OC, 13C-OC, 14C-OC and terrestrial biomarkers from the published literature and yet-unpublished records. This offers the opportunity to study large-scale remobilization of terrOC in the circum-Arctic by integrating input from terrOC sources over large areas. Mass accumulation rates of the different terrOC sources (by 210Pb dating and dual-isotope source apportionment of OC) reveal that surface (incl. permafrost) soils remobilize more than twice as much terrOC as coastal erosion of old Pleistocene permafrost. Furthermore, vulnerabilities of terrOC stocks to large-scale remobilization are discussed, which suggests permafrost soils to be the most vulnerable terrOC pool to remobilization by climate warming. This thesis highlights the vulnerability of terrOC stores to Arctic warming over time and space, and thus contributes to a better understanding of climate-carbon couplings in the Earth system.
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| 22. |
- Matsubara, Felipe, 1991-, et al.
(författare)
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Molecular-Multiproxy Assessment of Land-Derived Organic Matter Degradation Over Extensive Scales of the East Siberian Arctic Shelf Seas
- 2022
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 36:12
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Tidskriftsartikel (refereegranskat)abstract
- Global warming triggers permafrost thaw, which increases the release of terrigenous organic matter (terr-OM) to the Arctic Ocean by coastal erosion and rivers. Terrigenous OM degradation in the Arctic Ocean contributes to greenhouse gas emissions and severe ocean acidification, yet the vulnerability of different terr-OM components is poorly resolved. Here, terr-OM degradation dynamics are studied with unprecedented spatial coverage over the World's largest shelf sea system—the East Siberian Arctic Shelf (ESAS), using a multi-proxy molecular biomarker approach. Mineral-surface-area-normalized concentrations of terr-OM compounds in surface sediments decreases offshore. Differences between terr-OM compound classes (lignin phenols, high-molecular weight [HMW] n-alkanes, n-alkanoic acids and n-alkanols, sterols, 3,5-dihydroxybenzoic acids, cutin acids) reflect contrasting influence of sources, propensity to microbial degradation and association with sedimenting particles, with lignin phenols disappearing 3-times faster than total terr-OM, and twice faster than other biomarkers. Molecular degradation proxies support substantial terr-OM degradation across the ESAS, with clearest trends shown by: 3,5-dihydroxybenzoic acid/vanillyl phenol ratios, acid-to-aldehyde ratios of syringyl and vanillyl phenols, Carbon Preference Indices of HMW n-alkyl compounds and sitostanol/β-sitosterol. The combination of terr-OM biomarker data with δ13C/Δ14C-based source apportionment indicates that the more degraded state of lignin is influenced by the relative contribution of river-transported terr-OM from surface soils, while HMW n-alkanoic acids and stigmasterol are influenced by erosion-derived terr-OM from Ice Complex deposits. Our findings demonstrate differences in vulnerability to degradation between contrasting terr-OM pools, and underscore the need to consider molecular properties for understanding and modeling of large-scale biogeochemical processes of the permafrost carbon-climate feedback.
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| 23. |
- Quentin, Audrey G, et al.
(författare)
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Non-structural carbohydrates in woody plants compared among laboratories.
- 2015
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Ingår i: Tree physiology. - : Oxford University Press (OUP). - 1758-4469 .- 0829-318X. ; 35:11, s. 1146-1165
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Tidskriftsartikel (refereegranskat)abstract
- Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g(-1) for starch and 53-649 (mean = 153) mg g(-1) for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R(2) = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g(-1) for total NSC, compared with the range of laboratory estimates of 596 mg g(-1). Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.
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| 24. |
- Ray, Nicholas E., et al.
(författare)
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The Role of Coastal Yedoma Deposits and Continental Shelf Sediments in the Arctic Ocean Silicon Cycle
- 2024
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 38:1
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Tidskriftsartikel (refereegranskat)abstract
- The availability of silicon (Si) in the ocean plays an important role in regulating biogeochemical and ecological processes. The Si budget of the Arctic Ocean appears balanced, with inputs equivalent to outputs, though it is unclear how a changing climate might aggravate this balance. In this study, we focus on Si cycling in Arctic coastal areas and continental shelf sediments to better constrain the Arctic Ocean Si budget. We provide the first estimate of amorphous Si (ASi) loading from erosion of coastal Yedoma deposits (30-90 Gmol yr-1), demonstrating comparable rates to particulate Si loading from rivers (10-90 Gmol yr-1). We found a positive relationship between surface sediment ASi and organic matter content on continental shelves. Combining these values with published Arctic shelf sediment properties and burial rates we estimate 70 Gmol Si yr-1 is buried on Arctic continental shelves, equivalent to 4.5% of all Si inputs to the Arctic Ocean. Sediment dissolved Si fluxes increased with distance from river mouths along cruise transects of shelf regions influenced by major rivers in the Laptev and East Siberian seas. On an annual basis, we estimate that Arctic shelf sediments recycle approximately up to twice as much DSi (680 Gmol Si) as is loaded from rivers (340-500 Gmol Si). Coastal erosion loads 30-90 Gmol Si yr-1 to the Arctic Ocean in the form of amorphous siliconContinental shelf sediments in the Arctic Ocean recycle more silicon than is loaded from riversApproximately 4.5% of silicon loaded on the Arctic Ocean is buried in continental shelf sediments
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| 25. |
- Santruckova, Hana, et al.
(författare)
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Significance of dark CO2 fixation in arctic soils
- 2018
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 119, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of dark fixation of CO2 by heterotrophic microorganisms in soil is generally accepted, but its importance for microbial metabolism and soil organic carbon (C) sequestration is unknown, especially under C limiting conditions. To fill this knowledge gap, we measured dark (CO2)-C-13 incorporation into soil organic matter and conducted a C-13-labelling experiment to follow the C-13 incorporation into phospholipid fatty acids as microbial biomass markers across soil profiles of four tundra ecosystems in the northern circumpolar region, where net primary productivity and thus soil C inputs are low. We further determined the abundance of various carboxylase genes and identified their microbial origin with metagenomics. The microbial capacity for heterotrophic CO2 fixation was determined by measuring the abundance of carboxylase genes and the incorporation of C-13 into soil C following the augmentation of bioavailable C sources. We demonstrate that dark CO2 fixation occurred ubiquitously in arctic tundra soils, with increasing importance in deeper soil horizons, presumably due to increasing C limitation with soil depth. Dark CO2 fixation accounted on average for 0.4, 1.0, 1.1, and 16% of net respiration in the organic, cryoturbated organic, mineral and permafrost horizons, respectively. Genes encoding anaplerotic enzymes of heterotrophic microorganisms comprised the majority of identified carboxylase genes. The genetic potential for dark CO2 fixation was spread over a broad taxonomic range. The results suggest important regulatory function of CO2 fixation in C limited conditions. The measurements were corroborated by modeling the long-term impact of dark CO2 fixation on soil organic matter. Our results suggest that increasing relative CO2 fixation rates in deeper soil horizons play an important role for soil internal C cycling and can, at least in part, explain the isotopic enrichment with soil depth.
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