| 1. |
- Ackermann, Kathrin, et al.
(författare)
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N-2 Fixation in Feather Mosses is a Sensitive Indicator of N Deposition in Boreal Forests
- 2012
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 15:6, s. 986-998
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) fixation in the feather moss-cyanobacteria association represents a major N source in boreal forests which experience low levels of N deposition; however, little is known about the effects of anthropogenic N inputs on the rate of fixation of atmospheric N-2 in mosses and the succeeding effects on soil nutrient concentrations and microbial community composition. We collected soil samples and moss shoots of Pleurozium schreberi at six distances along busy and remote roads in northern Sweden to assess the influence of road-derived N inputs on N-2 fixation in moss, soil nutrient concentrations and microbial communities. Soil nutrients were similar between busy and remote roads; N-2 fixation was higher in mosses along the remote roads than along the busy roads and increased with increasing distance from busy roads up to rates of N-2 fixation similar to remote roads. Throughfall N was higher in sites adjacent to the busy roads but showed no distance effect. Soil microbial phospholipid fatty acid (PLFA) composition exhibited a weak pattern regarding road type. Concentrations of bacterial and total PLFAs decreased with increasing distance from busy roads, whereas fungal PLFAs showed no distance effect. Our results show that N-2 fixation in feather mosses is highly affected by N deposition, here derived from roads in northern Sweden. Moreover, as other measured factors showed only weak differences between the road types, atmospheric N-2 fixation in feather mosses represents a highly sensitive indicator for increased N loads to natural systems.
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| 2. |
- Bay, Guillaume, et al.
(författare)
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Boreal feather mosses secrete chemical signals to gain nitrogen
- 2013
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 200:1, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- The mechanistic basis of feather moss-cyanobacteria associations, a main driver of nitrogen (N) input into boreal forests, remains unknown. Here, we studied colonization by Nostoc sp. on two feather mosses that form these associations (Pleurozium schreberi and Hylocomium splendens) and two acrocarpous mosses that do not (Dicranum polysetum and Polytrichum commune). We also determined how N availability and moss reproductive stage affects colonization, and measured N transfer from cyanobacteria to mosses. The ability of mosses to induce differentiation of cyanobacterial hormogonia, and of hormogonia to then colonize mosses and re-establish a functional symbiosis was determined through microcosm experiments, microscopy and acetylene reduction assays. Nitrogen transfer between cyanobacteria and Pleurozium schreberi was monitored by secondary ion mass spectrometry (SIMS). All mosses induced hormogonia differentiation but only feather mosses were subsequently colonized. Colonization on Pleurozium schreberi was enhanced during the moss reproductive phase but impaired by elevated N. Transfer of N from cyanobacteria to their host moss was observed. Our results reveal that feather mosses likely secrete species-specific chemo-attractants when N-limited, which guide cyanobacteria towards them and from which they gain N. We conclude that this signalling is regulated by N demands of mosses, and serves as a control of N input into boreal forests.
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| 3. |
- Bergman, Ingela, et al.
(författare)
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Deglaciation and colonization : Pioneer settlements in northern Fennoscandia
- 2004
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Ingår i: Journal of world prehistory. - New York : Plenum. - 0892-7537 .- 1573-7802. ; 18:2, s. 155-177
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Tidskriftsartikel (refereegranskat)abstract
- We present new data on Early Mesolithic settlements in northern Sweden and discuss the process of pioneer colonization. A new set of radiocarbon dates from archaeological sites push deglaciation of northern Fennoscandia further back in time and demonstrate the rapid arrival of pioneer settlers. Environmental data reveal a highly productive early postglacial setting with plant communities unmatched in present ecosystems. The chronological and technological setting supports immigration from the north and northwest with pioneers relying on a long history of enculturating northern subarctic landscapes.
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| 4. |
- Bergman, Ingela, et al.
(författare)
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Early Mesolithic Hunter–Gatherers and Landscape Acquisition by the Arctic Circle : The Ipmatis valley 7000 BC–1 AD
- 2007
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Ingår i: Journal of Northern Studies. - Umeå : Umeå University; The Royal Skyttean Society. - 1654-5915 .- 2004-4658. ; 1:1-2, s. 123-142
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Tidskriftsartikel (refereegranskat)abstract
- Archaeological and palaeoecological studies in the Arjeplog area of northern Sweden have verified the arrival of hunter–gatherers soon after deglaciation. After modelling and subsequently surveying the reconstructed shorelines of tilted watercourses, Early Mesolithic settlements dating to 8600–8000 BP (14C years BP) were discovered. Makrosubfossil-, pollen- and charcoal analyses of peat stratigrafies and lake sediments corroborated that deglaciation was completed more than 1000 years earlier than has previously been postulated. Pollen records show that the early postglacial environment included complex plant communities lacking present day analogies, providing optimal subsistence conditions for the pioneer settlers. Studies of charcoal influx into lake sediments indicate that fires were more frequent than ever after, contributing to a productive natural environment. Regional studies in the Ipmatis valley in combination with in-depth analyses of selected archaeological sites, display that hunter–gatherers made the resources of the valley an integral part of their subsistence at an early stage. Landscape acquisition included not only the adjustment to existing conditions, but the actual manipulation of the environment. The interdisciplinary research approach has produced unique sets of archaeological and palaeoecological data. Results open new perspectives on human pioneer colonisation and landscape acquisition in relation to deglaciation and the development of postglacial ecosystems. The variety of methods applied sets a new standard for future research on early societies in sub-arctic regions.
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| 5. |
- DeLuca, Thomas H., et al.
(författare)
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Diazotrophy in Alluvial Meadows of Subarctic River Systems
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:11
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Tidskriftsartikel (refereegranskat)abstract
- There is currently limited understanding of the contribution of biological N-2 fixation (diazotrophy) to the N budget of large river systems. This natural source of N in boreal river systems may partially explain the sustained productivity of river floodplains in Northern Europe where winter fodder was harvested for centuries without fertilizer amendments. In much of the world, anthropogenic pollution and river regulation have nearly eliminated opportunities to study natural processes that shaped early nutrient dynamics of large river systems; however, pristine conditions in northern Fennoscandia allow for the retrospective evaluation of key biochemical processes of historical significance. We investigated biological N-2 fixation (diazotrophy) as a potential source of nitrogen fertility at 71 independent floodplain sites along 10 rivers and conducted seasonal and intensive analyses at a subset of these sites. Biological N-2 fixation occurred in all floodplains, averaged 24.5 kg N ha(-1) yr(-1) and was down regulated from over 60 kg N ha(-1) yr(-1) to 0 kg N ha(-1) yr(-1) by river N pollution. A diversity of N-2-fixing cyanobacteria was found to colonize surface detritus in the floodplains. The data provide evidence for N-2 fixation to be a fundamental source of new N that may have sustained fertility at alluvial sites along subarctic rivers. Such data may have implications for the interpretation of ancient agricultural development and the design of contemporary low-input agroecosystems.
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| 6. |
- DeLuca, Thomas H, et al.
(författare)
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Ecosystem controls on nitrogen fixation in boreal feather moss communities.
- 2007
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 152:1, s. 121-30
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Tidskriftsartikel (refereegranskat)abstract
- N fixation in feather moss carpets is maximized in late secondary successional boreal forests; however, there is limited understanding of the ecosystem factors that drive cyanobacterial N fixation in feather mosses with successional stage. We conducted a reciprocal transplant experiment to assess factors in both early and late succession that control N fixation in feather moss carpets dominated by Pleurozium schreberi. In 2003, intact microplots of moss carpets (30 cm × 30 cm × 10–20 cm deep) were excavated from three early secondary successional (41–101 years since last fire) forest sites and either replanted within the same stand or transplanted into one of three late successional (241–356 years since last fire) forest sites and the transverse was done for late successional layers of moss. Moss plots were monitored for changes in N-fixation rates by acetylene reduction (June 2003–September 2005) and changes in the presence of cyanobacteria on moss shoots by microscopy (2004). Forest nutrient status was measured using ionic resin capsules buried in the humus layer. Late successional forests exhibit high rates of N fixation and consistently high numbers of cyanobacteria on moss shoots, but low levels of available N. Conversely, early successional forests have higher N availability and have low rates of N fixation and limited presence of cyanobacteria on moss shoots. Transplantation of moss carpets resulted in a significant shift in presence and activity of cyanobacteria 1 year after initiation of the experiment responding to N fertility differences in early versus late successional forests.
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| 7. |
- Gentili, Francesco, et al.
(författare)
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Physiological and molecular diversity of feather moss associative N2-fixing cyanobacteria.
- 2005
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Ingår i: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 56:422, s. 3121-7
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Tidskriftsartikel (refereegranskat)abstract
- Cyanobacteria colonizing the feather moss Pleurozium schreberi were isolated from moss samples collected in northern Sweden and subjected to physiological and molecular characterization. Morphological studies of isolated and moss-associated cyanobacteria were carried out by light microscopy. Molecular tools were used for cyanobacteria identification, and a reconstitution experiment of the association between non-associative mosses and cyanobacteria was conducted. The influence of temperature on N2 fixation in the different cyanobacterial isolates and the influence of light and temperature on N2-fixation rates in the moss were studied using the acetylene reduction assay. Two different cyanobacteria were effectively isolated from P. schreberi: Nostoc sp. and Calothrix sp. A third genus, Stigonema sp. was identified by microscopy, but could not be isolated. The Nostoc sp. was found to fix N2 at lower temperatures than Calothrix sp. Nostoc sp. and Stigonema sp. were the predominant cyanobacteria colonizing the moss. The attempt to reconstitute the association between the moss and cyanobacteria was successful. The two isolated genera of cyanobacteria in feather moss samples collected in northern Sweden differ in their temperature optima, which may have important ecological implications.
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| 8. |
- Hörberg, Lisa, et al.
(författare)
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Reproducibility of measurements with a semi-automatic software package for the evaluation of rectal cancer
- 2020
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 61:5, s. 586-594
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Tidskriftsartikel (refereegranskat)abstract
- Background: Staging of rectal cancer with MRI has major impact on treatment choice and may be of importance in new cancer management strategies such as “wait-and-see” policy. Purpose: To assess the reproducibility of a software package recently developed at our department to measure volumes, apparent diffusion coefficient, and the skewness of apparent diffusion coefficient in lymph nodes and tumors in rectal cancer patients before and after chemoradiation treatment. Material and Methods: This study included 20 consecutive patients with biopsy-verified rectal cancer, in whom MRI staging had been performed both before and after chemoradiation treatment. The diffusion-weighted images were transferred to the software. The volume, apparent diffusion coefficient, and skewness were determined for 93 lymph nodes and 40 tumors. The volumes were compared with manual measurements of the volume of the same lymph nodes and tumors. Results: The agreement in semi-automatic measurements of lymph nodes was very good (ICC = 0.99), and in tumors good (ICC = 0.88). The agreement in manual measurements of lymph nodes was very good (ICC = 0.95) when all lymph nodes were included, but low (ICC = 0.52) if three outliers were excluded. Bland–Altman plots showed clear agreement between manual and semi-automatic measurements in the lymph nodes, but not in measurements of tumors. The values of apparent diffusion coefficient and skewness in tumors differed before and after treatment but did not differ in lymph nodes as a group. Conclusion: The software package showed a high degree of reproducibility in measurements on lymph nodes but requires further development to improve the reproducibility of tumor measurements.
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| 9. |
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| 10. |
- Jutesten, Henrik, et al.
(författare)
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Radiological findings in anastomotic leakage after anterior resection may predict a permanent stoma
- 2020
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Ingår i: Acta Radiologica Open. - : SAGE Publications. - 2058-4601. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Permanent stoma (PS) is common following treatment of anastomotic leakage (AL) after anterior resection (AR) and ways of predicting successful treatment outcome are missing.Purpose: To explore radiological variables in rectal contrast studies in their relation to end-result of PS following treatment for AL after AR.Material and Methods: The Swedish Cancer Registry (SCRCR) was explored for AL cases after AR for rectal cancer in patients operated in the region of Skåne from 1 January 2001 to 31 December 2011. Among identified AL cases, patients subjected to radiological imaging consistent with AL were evaluated according to a predetermined set of radiological variables. Information of PS as the end-result after AL treatment were retrieved from medical records.Results: Thirty-two patients had radiological imaging available for analysis confirming AL after AR; PS rate after a median follow-up of 87 months (range = 21-165) after AR was 62%. Radiological findings compatible with abscess (P = 0.023) and a leak size ≤6 mm (P = 0.049) were significantly associated with PS.Conclusion: In this limited explorative study, our findings suggest that abscess status and leak size could correspond to outcome of PS in treatment for AL after AR. Additional studies are warranted to further explore this subject.
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