| 1. |
- Devarajan, Raman, et al.
(author)
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Targeting collagen XVIII improves the efficiency of ErbB inhibitors in breast cancer models
- 2023
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In: Journal of Clinical Investigation. - : American Society for Clinical Investigation. - 0021-9738 .- 1558-8238. ; 133:18
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Journal article (peer-reviewed)abstract
- The tumor extracellular matrix (ECM) critically regulates cancer progression and treatment response. Expression of the basement membrane component collagen XVIII (ColXVIII) is induced in solid tumors, but its involvement in tumorigenesis has remained elusive. We show here that ColXVIII was markedly upregulated in human breast cancer (BC) and was closely associated with a poor prognosis in high-grade BCs. We discovered a role for ColXVIII as a modulator of epidermal growth factor receptor tyrosine kinase (ErbB) signaling and show that it forms a complex with ErbB1 and -2 (also known as EGFR and human epidermal growth factor receptor 2 [HER2]) and α6-integrin to promote cancer cell proliferation in a pathway involving its N-terminal portion and the MAPK/ERK1/2 and PI3K/AKT cascades. Studies using Col18a1 mouse models crossed with the mouse mammary tumor virus-polyoma virus middle T antigen (MMTV-PyMT) mammary carcinogenesis model showed that ColXVIII promoted BC growth and metastasis in a tumor cell-autonomous manner. Moreover, the number of mammary cancer stem cells was significantly reduced in the MMTV-PyMT and human cell models upon ColXVIII inhibition. Finally, ablation of ColXVIII substantially improved the efficacy of ErbB-targeting therapies in both preclinical models. In summary, ColXVIII was found to sustain the stemness properties of BC cells and tumor progression and metastasis through ErbB signaling, suggesting that targeting ColXVIII in the tumor milieu may have important therapeutic potential.
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| 2. |
- Thulin, Åsa, et al.
(author)
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Activated platelets provide a functional microenvironment for the antiangiogenic fragment of histidine-rich glycoprotein
- 2009
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In: Molecular Cancer Research. - 1541-7786 .- 1557-3125. ; 7:11, s. 1792-1802
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Journal article (peer-reviewed)abstract
- The angiogenesis inhibitor histidine-rich glycoprotein (HRG) constitutes one of several examples of molecules regulating both angiogenesis and hemostasis. The antiangiogenic properties of HRG are mediated via its proteolytically released histidine- and proline-rich (His/Pro-rich) domain.Using a combination of immunohistochemistry and massspectrometry, we here provide biochemical evidence for thepresence of a proteolytic peptide, corresponding to the antiangiogenic domain of HRG, in vivo in human tissue. This finding supports a role for HRG as an endogenous regulator of angiogenesis. Interestingly, the His/Pro-rich peptide bound to the vessel wall in tissue from cancer patients but not to the vasculature in tissue from healthy persons.Moreover, the His/Pro-rich peptide was found in close association with platelets. Relesate from in vitro–activated platelets promoted binding of the His/Pro-rich domain of HRG to endothelial cells, an effect mediated by Zn2+.Previous studies have shown that zinc-dependent bindingof the His/Pro-rich domain of HRG to heparan sulfate on endothelial cells is required for inhibition of angiogenesis.We describe a novel mechanism to increase the local concentration and activity of an angiogenesis inhibitor,which may reflect a host response to counteract angiogenesis during pathologic conditions. Our finding that tumor angiogenesis is elevated in HRG-deficient mice supports this conclusion.
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| 3. |
- Tuomi, Maria, et al.
(author)
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Stomping in silence : Conceptualizing trampling effects on soils in polar tundra
- 2021
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In: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 35:2, s. 306-317
-
Research review (peer-reviewed)abstract
- Ungulate trampling modifies soils and interlinked ecosystem functions across biomes. Until today, most research has focused on temperate ecosystems and mineral soils while trampling effects on cold and organic matter-rich tundra soils remain largely unknown. We aimed to develop a general model of trampling effects on soil structure, biota, microclimate and biogeochemical processes, with a particular focus on polar tundra soils. To reach this goal, we reviewed literature about the effects of trampling and physical disturbances on soils across biomes and used this to discuss the knowns and unknowns of trampling effects on tundra soils. We identified the following four pathways through which trampling affects soils: (a) soil compaction; (b) reductions in soil fauna and fungi; (c) rapid losses in vegetation biomass and cover; and (d) longer term shifts in vegetation community composition. We found that, in polar tundra, soil responses to trampling pathways 1 and 3 could be characterized by nonlinear dynamics and tundra-specific context dependencies that we formulated into testable hypotheses. In conclusion, trampling may affect tundra soil significantly but many direct, interacting and cascading responses remain unknown. We call for research to advance the understanding of trampling effects on soils to support informed efforts to manage and predict the functioning of tundra systems under global changes. A free Plain Language Summary can be found within the Supporting Information of this article.
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| 4. |
- Ahonen, Saija H K, et al.
(author)
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Reindeer grazing history determines the responses of subarctic soil fungal communities to warming and fertilization
- 2021
-
In: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 232:2, s. 788-801
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Journal article (peer-reviewed)abstract
- Composition and functioning of arctic soil fungal communities may alter rapidly due to the ongoing trends of warmer temperatures, shifts in nutrient availability and shrub encroachment. In addition, the communities may also be intrinsically shaped by heavy grazing, which may locally induce an ecosystem change that couples with increased soil temperature and nutrients and where shrub encroachment is less likely to occur than in lightly grazed conditions. We tested how four years of experimental warming and fertilization affected organic soil fungal communities in sites with decadal history of either heavy or light reindeer grazing using high-throughput sequencing of ITS2 rDNA region. Grazing history largely overrode the impacts of short-term warming and fertilization in determining the composition of fungal communities. The less diverse fungal communities under light grazing showed more pronounced responses to experimental treatments when compared to the communities under heavy grazing. Yet, ordination approaches revealed distinct treatment responses under both grazing intensities. If grazing shifts the fungal communities in Arctic ecosystems to a different and more diverse state, this shift may dictate ecosystem responses to further abiotic changes. This inclines that the intensity of grazing cannot be left out when predicting future changes in fungi-driven processes in the tundra.
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| 5. |
- Barthelemy, Hélène, et al.
(author)
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Short- and long-term plant and microbial uptake of 15N-labelled urea in a mesic tundra heath, West Greenland
- 2024
-
In: Polar Biology. - : Springer Nature. - 0722-4060 .- 1432-2056. ; 47:1, s. 1-15
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Journal article (peer-reviewed)abstract
- Terrestrial animals are key elements in the cycling of elements in the Arctic where nutrient availability is low. Waste production by herbivores, in particular urine deposition, has a crucial role for nitrogen (N) recycling, still, it remains largely unexplored. Also, experimental evidence is biased toward short-term studies and Arctic regions under high herbivore pressure. In this study, we aimed to examine the fate of N derived from urine in a nutrient poor tundra heath in West Greenland, with historical low level of herbivory. We performed a pulse labelling with 15N-urea over the plant canopy and explored ecosystem N partition and retention in the short-term (2 weeks and 1 year) and longer-term (5 years). We found that all vascular plants, irrespective of their traits, could rapidly take up N-urea, but mosses and lichens were even more efficient. Total 15N enrichment was severely reduced for all plants 5 years after tracer addition, with the exception of cryptogams, indicating that non-vascular plants constituted a long-term sink of 15N-urea. The 15N recovery was also high in the litter suggesting high N immobilization in this layer, potentially delaying the nutrients from urine entering the soil compartment. Long-term 15N recovery in soil microbial biomass was minimal, but as much as 30% of added 15N remained in the non-microbial fraction after 5 years. Our results demonstrate that tundra plants that have evolved under low herbivory pressure are well adapted to quickly take advantage of labile urea, with urine having only a transient effect on soil nutrient availability.
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| 6. |
- Gavazov, Konstantin, 1983-, et al.
(author)
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Plant-microbial linkages underpin carbon sequestration in contrasting mountain tundra vegetation types
- 2022
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In: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 165
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Journal article (peer-reviewed)abstract
- Tundra ecosystems hold large stocks of soil organic matter (SOM), likely due to low temperatures limiting rates of microbial SOM decomposition more than those of SOM accumulation from plant primary productivity and microbial necromass inputs. Here we test the hypotheses that distinct tundra vegetation types and their carbon supply to characteristic rhizosphere microbes determine SOM cycling independent of temperature. In the subarctic Scandes, we used a three-way factorial design with paired heath and meadow vegetation at each of two elevations, and with each combination of vegetation type and elevation subjected during one growing season to either ambient light (i.e., ambient plant productivity), or 95% shading (i.e., reduced plant productivity). We assessed potential above- and belowground ecosystem linkages by uni- and multivariate analyses of variance, and structural equation modelling. We observed direct coupling between tundra vegetation type and microbial community composition and function, which underpinned the ecosystem's potential for SOM storage. Greater primary productivity at low elevation and ambient light supported higher microbial biomass and nitrogen immobilisation, with lower microbial mass-specific enzymatic activity and SOM humification. Congruently, larger SOM at lower elevation and in heath sustained fungal-dominated microbial communities, which were less substrate-limited, and invested less into enzymatic SOM mineralisation, owing to a greater carbon-use efficiency (CUE). Our results highlight the importance of tundra plant community characteristics (i.e., productivity and vegetation type), via their effects on soil microbial community size, structure and physiology, as essential drivers of SOM turnover. The here documented concerted patterns in above- and belowground ecosystem functioning is strongly supportive of using plant community characteristics as surrogates for assessing tundra carbon storage potential and its evolution under climate and vegetation changes.
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| 7. |
- Gylling, Mikhail, et al.
(author)
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The hypoparathyroidism of autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy protective effect of male sex
- 2003
-
In: Journal of Clinical Endocrinology and Metabolism. - 0021-972X .- 1945-7197. ; 88:10, s. 4602-4608
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Journal article (other academic/artistic)abstract
- In autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, hypoparathyroidism (HP) is the most common endocrine component. It occurs in most (but not all) patients. Determinants of its occurrence are unknown, and there is no proof for its autoimmune nature. Recently, the Ca(2+)-sensing receptor (CaSR) was reported to be an autoantigen in HP. With our group of 90 patients, we aimed at identifying the determinants and pathomechanism of HP. For the determinants, we evaluated gender and the HLA class II. For the pathomechanism, we searched for parathyroid autoantibodies, including antibodies against CaSR and PTH. Also, we studied whether AIRE is expressed in the human parathyroid, because its absence could be a pathogenetic factor. We found a clear gender linkage with lower and later incidence in males. Of the 14 patients who had escaped HP, 13 were males. This was associated with adrenal failure, which was the first or only endocrinopathy in 47% of males vs. 7% of females. In contrast, we found no linkage to the HLA class II. By immunofluorescence, 19% of the patients had antibodies to parathyroid epithelia. By immunoblotting, these recognized several parathyroid proteins. No antibodies were observed against the CaSR or PTH. By RT-PCR, AIRE mRNA was not found in the parathyroid.
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| 8. |
- Kirchhoff, Leah, et al.
(author)
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Microbial community composition unaffected by mycorrhizal plant removal in sub-arctic tundra
- 2024
-
In: Fungal ecology. - 1754-5048 .- 1878-0083. ; 69
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Journal article (peer-reviewed)abstract
- Vegetation changes in a warming Arctic may affect plant-associated soil microbial communities with possible consequences for the biogeochemical cycling of carbon (C) and nitrogen (N). In a sub-arctic tundra heath, we factorially removed plant species with ecto- and ericoid mycorrhizal associations. After two years, we explored how mycorrhizal type-specific plant removal influences microbial communities, soil and microbial C and N pools, and extracellular enzymatic activities. Removal of ecto- and ericoid mycorrhizal plants did not change the soil fungal or bacterial community composition or their extracellular enzyme activities. However, ericoid plant removal decreased microbial C:N ratio, suggesting a stoichiometric effect decoupled from microbial community composition. In other words, microbial communities appear to show initial plasticity in response to major changes in tundra vegetation. This highlights the importance of longer-term perspectives when investigating the effects of vegetation changes on biogeochemical processes in Arctic ecosystems.
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| 9. |
- Monteux, Sylvain, 1989-, et al.
(author)
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Controlling biases in targeted plant removal experiments
- 2024
-
In: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 242:4, s. 1835-1845
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Journal article (peer-reviewed)abstract
- Targeted removal experiments are a powerful tool to assess the effects of plant species or (functional) groups on ecosystem functions. However, removing plant biomass in itself can bias the observed responses. This bias is commonly addressed by waiting until ecosystem recovery, but this is inherently based on unverified proxies or anecdotal evidence. Statistical control methods are efficient, but restricted in scope by underlying assumptions.We propose accounting for such biases within the experimental design, using a gradient of biomass removal controls. We demonstrate the relevance of this design by presenting (1) conceptual examples of suspected biases and (2) how to observe and control for these biases.Using data from a mycorrhizal association-based removal experiment, we show that ignoring biomass removal biases (including by assuming ecosystem recovery) can lead to incorrect, or even contrary conclusions (e.g. false positive and false negative). Our gradient design can prevent such incorrect interpretations, regardless of whether aboveground biomass has fully recovered.Our approach provides more objective and quantitative insights, independently assessed for each variable, than using a proxy to assume ecosystem recovery. Our approach circumvents the strict statistical assumptions of, for example, ANCOVA and thus offers greater flexibility in data analysis.
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| 10. |
- Rocher-Ros, Gerard, et al.
(author)
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Metabolism overrides photo-oxidation in CO2 dynamics of Arctic permafrost streams
- 2021
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In: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:S1, s. S169-S181
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Journal article (peer-reviewed)abstract
- Global warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO2 and released to the atmosphere. Abiotic photo‐oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO2 dynamics in aquatic ecosystems. We measured CO2 concentrations and the isotopic composition of dissolved inorganic C (δ13CDIC) at diel resolution in two Arctic streams, and coupled this with whole‐system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO2 concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo‐oxidation is the dominant source of CO2. Instead, the observed decrease in CO2 during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in δ13CDIC values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in δ13CDIC values, suggesting that metabolic estimates are partly masked by O2 consumption from photo‐oxidation. Our results suggest that 6–12 mmol CO2‐C m−2 d−1 may be generated from photo‐oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo‐oxidation rates for these Arctic streams, and accounted for 33–80% of total CO2 evasion. Our results suggest that metabolic activity is the dominant process for CO2 production in Arctic streams. Thus, future aquatic CO2 emissions may depend on how biotic processes respond to the ongoing environmental change.
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| 11. |
- Väisänen, Daniel, et al.
(author)
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Criterion validity of the Ekblom-Bak and the Åstrand submaximal test in an elderly population.
- 2020
-
In: European Journal of Applied Physiology. - : Springer. - 1439-6319 .- 1439-6327. ; 120:2, s. 307-316
-
Journal article (peer-reviewed)abstract
- PURPOSE: The aim of this study was to validate the submaximal Ekblom-Bak test (EB-test) and the Åstrand test (Å-test) for an elderly population.METHODS: Participants (n = 104), aged 65-75 years, completed a submaximal aerobic test on a cycle ergometer followed by an individually adjusted indirect calorimetry VO2max test on a treadmill. The HR from the submaximal test was used to estimate VO2max using both the EB-test and Å-test equations.RESULTS: The correlation between measured and estimated VO2max using the EB method and Å method in women was r = 0.64 and r = 0.58, respectively and in men r = 0.44 and r = 0.44, respectively. In women, the mean difference between estimated and measured VO2max was - 0.02 L min-1 (95% CI - 0.08 to 0.04) for the EB method and - 0.12 L min-1 (95% CI - 0.22 to - 0.02) for the Å method. Corresponding values for men were 0.05 L min-1 (95% CI - 0.04 to 0.14) and - 0.28 L min-1 (95% CI - 0.42 to - 0.14), respectively. However, the EB method was found to overestimate VO2max in men with low fitness and the Å method was found to underestimate VO2max in both women and men. For women, the coefficient of variance was 11.1%, when using the EB method and 19.8% when using the Å method. Corresponding values for men were 11.6% and 18.9%, respectively.CONCLUSION: The submaximal EB-test is valid for estimating VO2max in elderly women, but not in all elderly men. The Å-test is not valid for estimating VO2max in the elderly.
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| 12. |
- Väisänen, Daniel, et al.
(author)
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Validity in Ekblom-Bak Test and its Ability to Track Changes in an Elderly Population
- 2018
-
Conference paper (peer-reviewed)abstract
- Background: Maximal oxygen uptake (VO2max) has a high prognostic value for CVD and all cause mortality, however the test is hard to administer and requires a maximal effort, which can be arduous for an elderly population. The submaximal Ekblom-Bak cycle ergometer test (EB test) has shown to be valid in adults, but its applicability in an elderly population is unknown. Aim: The purpose of this study was to validate the submaximal EB test and to examine its ability to detect changes in VO2max in an elderly population. Methods: The sample consisted of 108 elderly participants; aged 65-75 years (54 women, 54 men) with a measured VO2max of 1.42-3.69 L/min. 34 women and 40 men performed a retest (VO2max 1.45-3.59 L/min) after an intervention period. During the intervention, participants performed 30 training sessions over 12 weeks where they cycled for 30 min at 65-75 % of maximal heart rate. On pre- and retests participants completed a submaximal Ekblom-Bak test. Directly after participants completed an individually adjusted VO2max test on a treadmill where VO2 max was measured using indirect calorimetry. Results: For the validation of the EB-test on an elderly population there was a correlation (R) between measured and estimated VO2max of 0.64 for women and 0.47 for men, mean (95% CI) difference was 0.01 (-0.45 - 0.07) for women and -0.05 (-0.11 - 0.07) for men. Standard error of the estimate was 0.17 for women and 0.31 for men. Coefficient of variation was 10 % for women and 11 % for men. When analyzing the ability of the EB test to track change in VO2max after a 12 week training intervention there was a significant (P<0.001) average increase in estimated VO2max of 0.11 L/min for both genders (CI for women 0.06 - 0.16 and for men 0.08 - 0.15), with no change in the measured values. Changes in the estimated values were linked to a decrease of the submaximal HR on both work rates (3.0 bpm and 3.2 bpm on the standard work rate and 5.4 bpm and 6.4 bpm on the higher work rate, for women and men, respectively) Conclusion: Validity of the EB-test in a population between 65-75 years was fairly good but we found larger standard error of the estimate for the men. The higher error for men in contrast to women could be derived from a difference in change of physiological variables that affect VO2max with increasing age. Since there was no change in measured VO2max while there was an improvement in estimated VO2max after the intervention, the EB-test appears to respond to changes in fitness that are not reflected in a VO2max. Grant funding: European Research Council.
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| 13. |
- Väisänen, Maria, et al.
(author)
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Carbon dynamics at frost-patterned tundra driven by long-term vegetation change rather than by short-term non-growing season warming
- 2017
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In: Biogeochemistry. - : Springer. - 0168-2563 .- 1573-515X. ; 136:1, s. 103-117
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Journal article (peer-reviewed)abstract
- Frost-patterned grounds, such as mostly barren frost boils surrounded by denser vegetation, are typical habitat mosaics in tundra. Plant and microbial processes in these habitats may be susceptible to short-term warming outside the growing season, while the areal cover of barren frost boils has decreased during the past decades due to climate warming-induced shrub expansion. The relative importance of such short-term and long-term climate impacts on carbon (C) dynamics remains unknown. We measured ecosystem CO2 uptake and release (in the field), microbial respiration (in the laboratory), as well as microbial biomass N and soil extractable N in frost boils and the directly adjacent heath in late spring and late summer. These habitats had been experimentally warmed with insulating fleeces from late September until late May for three consecutive years, which allowed us to investigate the direct short-term effects of warming and longer-term, indirect climate effects via vegetation establishment into frost boils. Non-growing season warming increased C uptake at the frost boils in late spring and decreased it in late summer, while the timing and direction of responses was opposite for the heath. Experimental warming had no effects on microbial or ecosystem C release or soil N at either of the habitats. However, C cycling was manifold higher at the heath compared to the frost boils, likely because of a higher SOM stock in the soil. Short-term climate change can thus directly alter ecosystem C uptake at frost-patterned grounds but will most likely not affect microbial C release. We conclude that the C dynamics at frost-patterned grounds under a changing climate depend most strongly on the potential of vegetation to encroach into frost boils in the long-term.
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| 14. |
- Väisänen, Maria, et al.
(author)
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Meshes in mesocosms control solute and biota exchange in soils : A step towards disentangling (a)biotic impacts on the fate of thawing permafrost
- 2020
-
In: Agriculture, Ecosystems & Environment. Applied Soil Ecology. - : Elsevier. - 0929-1393 .- 1873-0272. ; 151
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Journal article (peer-reviewed)abstract
- Environmental changes feedback to climate through their impact on soil functions such as carbon (C) and nutrient sequestration. Abiotic conditions and the interactions between above- and belowground biota drive soil responses to environmental change but these (a)biotic interactions are challenging to study. Nonetheless, better understanding of these interactions would improve predictions of future soil functioning and the soil-climate feedback and, in this context, permafrost soils are of particular interest due to their vast soil C-stores. We need new tools to isolate abiotic (microclimate, chemistry) and biotic (roots, fauna, microorganisms) components and to identify their respective roles in soil processes. We developed a new experimental setup, in which we mimic thermokarst (permafrost thaw-induced soil subsidence) by fitting thawed permafrost and vegetated active layer sods side by side into mesocosms deployed in a subarctic tundra over two growing seasons. In each mesocosm, the two sods were separated from each other by barriers with different mesh sizes to allow varying degrees of physical connection and, consequently, (a)biotic exchange between active layer and permafrost. We demonstrate that our mesh-approach succeeded in controlling 1) lateral exchange of solutes between the two soil types, 2) colonization of permafrost by microbes but not by soil fauna, and 3) ingrowth of roots into permafrost. In particular, experimental thermokarst induced a similar to 60% decline in permafrost nitrogen (N) content, a shift in soil bacteria and a rapid buildup of root biomass (+33.2 g roots m(-2) soil). This indicates that cascading plant-soil-microbe linkages are at the heart of biogeochemical cycling in thermokarst events. We propose that this novel setup can be used to explore the effects of (a)biotic ecosystem components on focal biogeochemical processes in permafrost soils and beyond.
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| 15. |
- Väisänen, Maria, et al.
(author)
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Phenolic responses of mountain crowberry (Empetrum nigrum ssp. hermaphroditum) to global climate change are compound specific and depend on grazing by reindeer (Rangifer tarandus)
- 2013
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In: Journal of Chemical Ecology. - : Springer. - 0098-0331 .- 1573-1561. ; 39:11-12, s. 1390-1399
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Journal article (peer-reviewed)abstract
- Mountain crowberry (Empetrum nigrum ssp. hermaphroditum) is a keystone species in northern ecosystems and exerts important ecosystem-level effects through high concentrations of phenolic metabolites. It has not been investigated how crowberry phenolics will respond to global climate change. In the tundra, grazing by reindeer (Rangifer tarandus) affects vegetation and soil nutrient availability, but almost nothing is known about the interactions between grazing and global climate change on plant phenolics. We performed a factorial warming and fertilization experiment in a tundra ecosystem under light grazing and heavy grazing and analyzed individual foliar phenolics and crowberry abundance. Crowberry was more abundant under light grazing than heavy grazing. Although phenolic concentrations did not differ between grazing intensities, responses of crowberry abundance and phenolic concentrations to warming varied significantly depending on grazing intensity. Under light grazing, warming increased crowberry abundance and the concentration of stilbenes, but decreased e.g., the concentrations of flavonols, condensed tannins, and batatasin-III, resulting in no change in total phenolics. Under heavy grazing, warming did not affect crowberry abundance, and induced a weak but consistent decrease among the different phenolic compound groups, resulting in a net decrease in total phenolics. Our results show that the different phenolic compound groups may show varying or even opposing responses to warming in the tundra at different levels of grazing intensity. Even when plant phenolic concentrations do not directly respond to grazing, grazers may have a key control over plant responses to changes in the abiotic environment, reflecting multiple adaptive purposes of plant phenolics and complex interactions between the biotic and the abiotic factors.
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| 16. |
- Väisänen, Maria, et al.
(author)
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The Legacy Effects of Winter Climate on Microbial Functioning After Snowmelt in a Subarctic Tundra
- 2019
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In: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 77:1, s. 186-190
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Journal article (peer-reviewed)abstract
- Warming-induced increases in microbial CO2 release in northern tundra may positively feedback to climate change. However, shifts in microbial extracellular enzyme activities (EEAs) may alter the impacts of warming over the longer term. We investigated the in situ effects of 3years of winter warming in combination with the in vitro effects of a rapid warming (6days) on microbial CO2 release and EEAs in a subarctic tundra heath after snowmelt in spring. Winter warming did not change microbial CO2 release at ambient (10 degrees C) or at rapidly increased temperatures, i.e., a warm spell (18 degrees C) but induced changes (P<0.1) in the Q(10) of microbial respiration and an oxidative EEA. Thus, although warmer winters may induce legacy effects in microbial temperature acclimation, we found no evidence for changes in potential carbon mineralization after spring thaw.
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| 17. |
- Väisänen, Maria, et al.
(author)
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Tundra cryogenic land surface processes and CO2–C balance in sub-Arctic alpine environment withstand winter and spring warming
- 2023
-
In: Environmental Research: Climate. - : Institute of Physics Publishing (IOPP). - 2752-5295. ; 2:2
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Journal article (peer-reviewed)abstract
- Cryogenic land surface processes (CLSPs), such as cryoturbation, are currently active in landscapes covering 25% of our planet where they dictate key functions, such as carbon (C) cycling, and maintain patterned landscape features. While CLSPs are expected to diminish in the near future due to milder winters especially in the southern parts of the Arctic, the shifts in C cycling in these landscapes may be more complex, since climate change can affect C cycling directly but also indirectly via CLSPs. Here, we study the effects of changing winter and spring climate on CLSPs and C cycling in non-sorted circles consisting of barren frost boils and their vegetated rims. We do this by measuring cryoturbation and ecosystem CO2 fluxes repeatedly in alpine subarctic tundra where temperatures during naturally snow covered period have been experimentally increased with snow-trapping fences and temperatures during winter and spring period after snowmelt have been increased with insulating fleeces. Opposite to our hypothesis, warming treatments did not decrease cryoturbation. However, winter warming via deeper snow increased ecosystem C sink during summer by decreasing ecosystem CO2 release in the frost boils and by counterbalancing the negative effects of cryoturbation on plant CO2 uptake in the vegetated rims. Our results suggest that short-term changes in winter and spring climate may not alter cryoturbation and jeopardize the tundra C sink.
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| 18. |
- Ylänne, Henni, et al.
(author)
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Removal of grazers alters the response of tundra soil carbon to warming and enhanced nitrogen availability
- 2020
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In: Ecological Monographs. - : Wiley. - 0012-9615 .- 1557-7015. ; 90:1
-
Journal article (peer-reviewed)abstract
- The circumpolar Arctic is currently facing multiple global changes that have the potential to alter the capacity of tundra soils to store carbon. Yet, predicting changes in soil carbon is hindered by the fact that multiple factors simultaneously control processes sustaining carbon storage and we do not understand how they act in concert. Here, we investigated the effects of warmer temperatures, enhanced soil nitrogen availability, and the combination of these on tundra carbon stocks at three different grazing regimes: on areas with over 50-yr history of either light or heavy reindeer grazing and in 5-yr-old exlosures in the heavily grazed area. In line with earlier reports, warming generally decreased soil carbon stocks. However, our results suggest that the mechanisms by which warming decreases carbon storage depend on grazing intensity: under long-term light grazing soil carbon losses were linked to higher shrub abundance and higher enzymatic activities, whereas under long-term heavy grazing, carbon losses were linked to drier soils and higher enzymatic activities. Importantly, under enhanced soil nitrogen availability, warming did not induce soil carbon losses under either of the long-term grazing regimes, whereas inside exclosures in the heavily grazed area, also the combination of warming and enhanced nutrient availability induced soil carbon loss. Grazing on its own did not influence the soil carbon stocks. These results reveal that accounting for the effect of warming or grazing alone is not sufficient to reliably predict future soil carbon storage in the tundra. Instead, the joint effects of multiple global changes need to be accounted for, with a special focus given to abrupt changes in grazing currently taking place in several parts of the Arctic.
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