| 1. |
- Boberg, Johanna, et al.
(författare)
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Decomposing capacity of fungi commonly detected in Pinus sylvestris needle litter
- 2011
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 4, s. 110-114
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Tidskriftsartikel (refereegranskat)abstract
- A major part of the fungal community in coniferous litter consists of fungi whose taxonomic position and ecology are unknown. Here, nine isolates from within commonly occurring phylogenetic groups were tested for their ability to decompose Pinus sylvestris needles. In a 1-yr long incubation study, needle mass loss as well as changes in cellulose and lignin content were determined and compared to those caused by two litter basidiomycetes (Marasmius androsaceus and Mycena epipterygia) with recognized ability to decompose needles. A basidiomycetous Clavulina/Sistotrema strain appeared to be cellulolytic but not ligninolytic. Chalara longipes and three other strains within Helotiales also decomposed cellulose but not lignin, whereas Mollisia cinerea (also Helotiales) and two Dothideomycetes - Sydowia polyspora and a Mytilinidion sp., seemed unable to cause significant mass loss of cellulose. Lophodermium pinastri (Rhytismatales) readily decomposed cellulose, and also caused considerable loss of lignin. (C) 2010 Elsevier Ltd and The British Mycological Society. All rights reserved.
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| 2. |
- Boberg, Johanna, et al.
(författare)
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Fungal C translocation restricts N-mineralization in heterogeneous environments
- 2010
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 24, s. 454-459
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Tidskriftsartikel (refereegranskat)abstract
- P>1. In forest soils, fungi generally dominate the decomposer community, but their specific, filamentous physiology is often not recognized in nitrogen (N) cycling models. Many litter degrading fungi form large mycelia and have a well-developed capacity to translocate resources within their mycelia. Fungi may thus connect substrates that differ with respect to carbon (C) and nitrogen (N) availability and, thereby, overcome local resource limitation through translocation.2. Here we test whether the ability of fungi to translocate carbohydrates within their mycelia prevents local C limitation in a low C:N ratio substrate, thereby reducing N mineralization. The capacity of fungi to translocate N to a high C:N ratio substrate in order to increase the decomposition, was also assessed. Two litter decomposing fungi, Marasmius androsaceus and Mycena epipterygia were grown in axenic laboratory microcosms containing spatially separated substrates: pine needles (C:N = 135) and glycine (C:N = 2).3. In the absence of needles both fungi mineralized the glycine N. When connecting the two substrates, both fungi were able to overcome local C-deficiency on the glycine medium by translocating carbohydrates from the needles. In the presence of needles, N mineralization from glycine was negligible, although the glycine was utilized. Only trace amounts of N were translocated from glycine to the needles.4. A basic assumption of N cycling models is that substrates of different qualities decompose in an independent manner. Our observations imply that this assumption may be violated in heterogenic environments dominated by fungi.
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| 3. |
- Boberg, Johanna, et al.
(författare)
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Nitrogen and Carbon Reallocation in Fungal Mycelia during Decomposition of Boreal Forest Litter
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 9:3, s. e92897-
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Tidskriftsartikel (refereegranskat)abstract
- Boreal forests are characterized by spatially heterogeneous soils with low N availability. The decomposition of coniferous litter in these systems is primarily performed by basidiomycete fungi, which often form large mycelia with a well-developed capacity to reallocate resources spatially-an advantageous trait in heterogeneous environments. In axenic microcosm systems we tested whether fungi increase their biomass production by reallocating N between Pinus sylvestris (Scots pine) needles at different stages of decomposition. We estimated fungal biomass production by analysing the accumulation of the fungal cell wall compound chitin. Monospecific systems were compared with systems with interspecific interactions. We found that the fungi reallocated assimilated N and mycelial growth away from well-degraded litter towards fresh litter components. This redistribution was accompanied by reduced decomposition of older litter. Interconnection of substrates increased over-all fungal C use efficiency (i.e. the allocation of assimilated C to biomass rather than respiration), presumably by enabling fungal translocation of growth-limiting N to litter with higher C quality. Fungal connection between different substrates also restricted N-mineralization and production of dissolved organic N, suggesting that litter saprotrophs in boreal forest ecosystems primarily act to redistribute rather than release N. This spatial integration of different resource qualities was hindered by interspecific interactions, in which litters of contrasting quality were colonised by two different basidiomycete species. The experiments provide a detailed picture of how resource reallocation in two decomposer fungi leads to a more efficient utilisation of spatially separated resources under N-limitation. From an ecosystem point of view, such economic fungal behaviour could potentially contribute to organic matter accumulation in the litter layers of boreal forests.
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| 4. |
- Boberg, Johanna, et al.
(författare)
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Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study
- 2011
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 4, s. 408-416
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Tidskriftsartikel (refereegranskat)abstract
- Fungi, especially basidiomycetous litter decomposers, are pivotal to the turnover of soil organic matter in forest soils. Many litter decomposing fungi have a well-developed capacity to translocate resources in their mycelia, a feature that may significantly affect carbon (C) and nitrogen (N) dynamics in decomposing litter. In an eight-month long laboratory study we investigated how the external availability of N affected the decomposition of Scots pine needles, fungal biomass production, N retention and N-mineralization by two litter decomposing fungi - Marasmius androsaceus and Mycena epipterygia. Glycine additions had a general, positive effect on fungal biomass production and increased accumulated needle mass loss after 8 months, suggesting that low N availability may limit fungal growth and activity in decomposing pine litter. Changes in the needle N pool reflected the dynamics of the fungal mycelium. During late decomposition stages, redistribution of mycelium and N out from the decomposed needles was observed for M. epipterygia, suggesting autophagous self degradation. (C) 2011 Elsevier Ltd and The British Mycological Society. All rights reserved.
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| 5. |
- Lindahl, Johanna, et al.
(författare)
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Circulation of Japanese Encephalitis Virus in Pigs and Mosquito Vectors within Can Tho City, Vietnam
- 2013
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Ingår i: PLoS Neglected Tropical Diseases. - : Public Library of Science (PLoS). - 1935-2727 .- 1935-2735. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Japanese encephalitis virus (JEV) is a mosquito-borne, zoonotic flavivirus causing encephalitis in humans and reproductive disorder in pigs. JEV is present in large parts of Asia, where urbanization is high. Households within and outside Can Tho city, South Vietnam, were selected to monitor circulation of JEV. A nested RT-PCR was established to detect the presence of JEV in mosquitoes whereas sera from pigs belonging to households within the province were analyzed for the presence of antibodies to JEV. A total of 7885 mosquitoes were collected and divided into 352 pools whereof seven were JEV-positive, six of which were collected within the city. Fragments from four pools clustered with JEV genotype III and three with genotype I. Of the 43 pigs sampled inside the city 100% had JEV antibodies. Our study demonstrates exposure to JEV in pigs, and co-circulation of JEV genotype I and III in mosquitoes within an urban environment in South Vietnam. Thus, although JEV has mainly been considered a rural disease, the potential for transmission in urban areas cannot be ignored.
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| 6. |
- Lindahl, Johanna
(författare)
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Japanese encephalitis virus in pigs and vectors in the Mekong Delta : with special reference to urban farming
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Japanese encephalitis Virus (JEV) is a mosquito-borne flavivirus in East and South Asia, estimated to cause 60 000 human cases of Japanese encephalitis each year. The main transmission cycle for JEV is via mosquito vectors, mainly Culex species, between pigs and wading birds, the reservoir hosts. Incidental infection in humans can result in encephalitis with 30% case fatalities, and half of the survivors may have neurological sequelae. Some of the most important vectors, such as Culex tritaeniorhynchus, commonly breed in rice fields, and the disease is therefore mainly considered to be a risk in rural areas. However, increasing urbanisation creates needs and opportunities for urban agriculture, and since pork is popular in Southeast Asia, it is common to keep pigs in cities. With this in mind, this thesis focuses on three important aspects of JEV circulation; the pig, the vectors and the virus itself. Pigs are usually only clinically affected by JEV during pregnancy. Sows in the area around Can Tho city in the Mekong delta region of South Vietnam, where JEV occurs endemically, were investigated for the association between JEV seropositivity and reproduction. In total 315 sows were included, with 60% seropositive. In sows less than 1.5 years of age, seropositivity was associated with the occurrence of more stillborn piglets, but this association could not be observed when all sows were included in the analysis. Mosquitoes were collected in households within and surrounding Can Tho city. The numbers of the zoophilic vectors Cx. tritaeniorhynchus and Culex gelidus were positively associated with pigs, whereas Culex quinquefasciatus, an anthropophilic vector, was positively associated with the number of people in the household. Of the 7885 mosquitoes collected, seven mosquito pools, collected close to pigs, were positive for JEV using nested RT-PCR. Four PCR fragments were similar to JEV genotype III and three to genotype I, indicating that both genotypes circulate in Can Tho city at the same time. Within Can Tho city all pigs sampled (43/43) were seropositive for JEV. These findings demonstrate that JEV can be a public health issue in urban as well as in rural areas and that it is associated with few reproductive problems in sows in an endemic area.
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| 7. |
- Lindahl, Johanna, et al.
(författare)
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Occurrence of Japanese Encephalitis Virus Mosquito Vectors in Relation to Urban Pig Holdings
- 2012
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Ingår i: American Journal of Tropical Medicine and Hygiene. - : American Society of Tropical Medicine and Hygiene. - 0002-9637 .- 1476-1645. ; 87, s. 1076-1082
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Tidskriftsartikel (refereegranskat)abstract
- Japanese encephalitis virus (JEV) is transmitted to humans from pigs or birds by mosquitoes. In this study, the association between urban pig keeping and mosquito vectors was analyzed. A total of 7, 419 mosquitoes were collected overnight in urban households with and without pigs in Can Tho City, Vietnam. The most prevalent vectors were Culex tritaeniorhynchus (36%), Cx. gelidus (24%), and Cx. quinquefasciatus (15%), which were present in all parts of the city. Pigs were associated with increased numbers of a. tritaeniorhynchus. Traps close to pigs had higher numbers of a. tritaeniorhynchus and Cx. gelidus than traps close to humans. Increased number of persons in the household was associated with increased numbers of Cx. quinquefasciatus. We demonstrate that JEV vector species are present at urban households with and without pigs, and show that keeping pigs in an urban area increase the number of mosquitoes competent as vectors for JEV.
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| 8. |
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| 9. |
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| 10. |
- Lindahl, Johanna, et al.
(författare)
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Reproductive performance in sows in relation to Japanese Encephalitis Virus seropositivity in an endemic area
- 2012
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Ingår i: Tropical Animal Health and Production. - : Springer Science and Business Media LLC. - 0049-4747 .- 1573-7438. ; 44, s. 239-245
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Tidskriftsartikel (refereegranskat)abstract
- Japanese Encephalitis Virus (JEV) is considered an important reproductive pathogen in pigs. Most studies of the reproductive impact of JEV have been conducted in areas where the disease occurs in seasonal epidemics. In this study, the associations between seropositivity for JEV, measured with an IgG ELISA, and the number of piglets born alive and stillborn were investigated in a tropical area endemic for JEV in Vietnam. Sixty percent of sows from four farms in the Mekong delta of Vietnam were seropositive to JEV and the Odds Ratio for a sow being infected was highest (6.4) in sows above 3.5 years (95% confidence interval 2.2-18.3). There was an association between increasing Optical Density (OD) values from the ELISA and the number of stillborn piglets in sows less than 1.5 years, but no effect of seropositivity could be shown when all sows were studied. OD values had an effect (p=0.04) on the number of piglets born alive in the statistical analysis only when interacting with the effect of the breeds. An increase in mean OD value of the herd was correlated (p<0.0001) with an increase in the number of piglets born alive. In this study, there was evidence of a negative association between seropositivity for JEV and the reproductive performance only in sows less than 1.5 years in endemic areas. This could be explained by a year-round infection with the virus, which would lead to immunity in many gilts before their first pregnancy. This, in turn, may imply that JEV infection in pigs is of minor importance for the reproductive performance in endemic areas.
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