| 1. |
- Adomas, Aleksandra, et al.
(författare)
-
Comparative analysis of transcript abundance in Pinus sylvestris after challenge with a saprotrophic, pathogenic or mutualistic fungus
- 2008
-
Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 28:6, s. 885-897
-
Tidskriftsartikel (refereegranskat)abstract
- To investigate functional differences in the recognition and response mechanisms of conifer roots to fungi with different trophic strategies, Pinus sylvestris L. was challenged with a saprotrophic fungus Trichoderma aureoviride Rifai. The results were compared with separate studies investigating pine interactions with a pathogen, Heterobasidion annosum (Fr.) Bref. sensu stricto and an ectomycorrhizal symbiont, Laccaria bicolor Maire (Orton). Global changes in the expression of 2109 conifer genes were assayed 1, 5 and 15 days after inoculation. Gene expression data from a cDNA microarray were analyzed by the 2-interconnected mixed linear model statistical approach. The total number of genes differentially expressed compared with the uninfected control was similar after challenge with the pathogen and the ectomycorrhizal symbiont, but the number of differentially expressed genes increased over time, for H. annosum, and decreased for L. bicolor. Inoculation of pine roots with T aureoviride resulted overall in a much lower number of genes with changed transcript levels compared with inoculation with H. annosum or L. bicolor. Functional classification of the differentially expressed genes revealed that the ectomycorrhizal fungus triggered transient induction of defence-related genes. The response and induction of defence against the pathogen was delayed and the magnitude increased over time. Thus, there were specific transcriptional responses depending on whether the conifer roots were challenged with mutualistic, saprotrophic or pathogenic fungi. This suggests that pine trees are able to recognize diverse fungal species and specifically distinguish whether they are pathogenic, neutral or beneficial microbial agents.
|
|
| 2. |
- Ahmed, Engy, 1985-
(författare)
-
Microbe-mineral interactions in soil : Investigation of biogenic chelators, microenvironments and weathering processes
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interplay between geology and biology has shaped the Earth during billions of years. Microbe-mineral interactions are prime examples of this interplay and underscore the importance of microorganisms in making Earth a suitable environment for all forms of life. The present thesis takes an interdisciplinary approach to obtain an integrated understanding of microbe-mineral interactions. More specifically it addresses how the composition and distribution of biogenic weathering agents (siderophores) differ with regard to soil horizon and mineral type in situ, what siderophore type soil microorganisms produces under laboratory conditions, what role microbial surface attachment plays in mineral weathering reactions and what central roles and applications siderophores have in the environment.Podzol, the third most abundant soil in Europe, and most abundant in Scandinavia, was chosen for a field experiment, where three minerals (apatite, biotite and oligoclase) were inserted in the organic, eluvial and upper illuvial soil horizons. The study started with an investigation of the siderophore composition in the bulk soil profile and on the mineral surfaces (paper I), which was followed by a study of the siderophore producing capabilities of microorganisms isolated from the soil profile under laboratory conditions (paper II). Subsequently, a study was done on the impact of microbial surface attachment on biotite dissolution (paper III). Finally, the roles of siderophores in nature and their potential applications were reviewed (paper IV).The major findings were that the concentration of hydroxamate siderophores in the soil attached to the mineral surfaces was greater than those in the surrounding bulk soil, indicating that the minerals stimulate the microbial communities attached to their surfaces to produce more siderophores than the microorganisms in the bulk soil. Each mineral had a unique assemblage of hydroxamate siderophores, that makes the mineral type one of the main factors affecting siderophore composition in the natural environment. Siderophore production varied between the microbial species originating from different soil horizons, suggesting that the metabolic properties of microbes in deep soil horizons function differently from those at upper soil horizons. Microbial surface attachment enhanced the biotite dissolution, showing that attached microbes has a greater influence on weathering reactions in soil than planktonic populations. In conclusion, our findings reflected that the complicated relationship between microorganisms and mineral surfaces reinforces the central theme of biogeochemistry that the mineral controls the biological activity in the natural environments. However, the importance of these relationships to the biogeochemical systems requires further investigation.
|
|
| 3. |
- Akselsson, Cecilia, et al.
(författare)
-
Weathering rates in Swedish forest soils
- 2019
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 16:22, s. 4429-4450
-
Forskningsöversikt (refereegranskat)abstract
- Soil and water acidification was internationally recognised as a severe environmental problem in the late 1960s. The interest in establishing “critical loads” led to a peak in weathering research in the 1980s and 1990s, since base cation weathering is the long-term counterbalance to acidification pressure. Assessments of weathering rates and associated uncertainties have recently become an area of renewed research interest, this time due to demand for forest residues to provide renewable bioenergy. Increased demand for forest fuels increases the risk of depleting the soils of base cations produced in situ by weathering. This is the background to the research programme Quantifying Weathering Rates for Sustainable Forestry (QWARTS), which ran from 2012 to 2019. The programme involved research groups working at different scales, from laboratory experiments to modelling. The aims of this study were to (1) investigate the variation in published weathering rates of base cations from different approaches in Sweden, with consideration of the key uncertainties for each method; (2) assess the robustness of the results in relation to sustainable forestry; and (3) discuss the results in relation to new insights from the QWARTS programme and propose ways to further reduce uncertainties. In the study we found that the variation in estimated weathering rates at single-site level was large, but still most sites could be placed reliably in broader classes of weathering rates. At the regional level, the results from the different approaches were in general agreement. Comparisons with base cation losses after stem-only and whole-tree harvesting showed sites where whole-tree harvesting was clearly not sustainable and other sites where variation in weathering rates from different approaches obscured the overall balance. Clear imbalances appeared mainly after whole-tree harvesting in spruce forests in southern and central Sweden. Based on the research findings in the QWARTS programme, it was concluded that the PROFILE/ForSAFE family of models provides the most important fundamental understanding of the contribution of weathering to long-term availability of base cations to support forest growth. However, these approaches should be continually assessed against other approaches. Uncertainties in the model approaches can be further reduced, mainly by finding ways to reduce uncertainties in input data on soil texture and associated hydrological parameters but also by developing the models, e.g. to better represent biological feedbacks under the influence of climate change.
|
|
| 4. |
- Boberg, Johanna, et al.
(författare)
-
Fungal C translocation restricts N-mineralization in heterogeneous environments
- 2010
-
Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 24, s. 454-459
-
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.
|
|
| 5. |
- Boberg, Johanna, et al.
(författare)
-
Nitrogen and Carbon Reallocation in Fungal Mycelia during Decomposition of Boreal Forest Litter
- 2014
-
Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 9:3, s. e92897-
-
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.
|
|
| 6. |
- Boberg, Johanna, et al.
(författare)
-
Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study
- 2011
-
Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 4, s. 408-416
-
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.
|
|
| 7. |
- Brun, Annick, et al.
(författare)
-
Structure and function of the ectomycorrhizal association between Paxillus involutus (Batsch) Fr. and Betula pendula Roth .L. Dynamics of mycorrhiza formation
- 1995
-
Ingår i: New Phytologist. - 1469-8137. ; 129:3, s. 487-493
-
Tidskriftsartikel (refereegranskat)abstract
- Detailed examination of the structural and functional integration taking place during mycorrhiza formation necessitates rapid and aseptic synthesis of uniform mycorrhizal structures at well-defined stages of development. A system is described for formation of ectomycorrhizas between Betula pendula Roth. and Paxillus involutus (Batsch) Fr. Small sterile seedlings were placed directly on fungal colonies growing on cellophane covered agar plates. Microscopic examination during the course of development indicated an initial rapid colonization of the roots and formation of a fully developed mantle within 2-4 d. Hartig net formation was evident after 8 d of contact and involved a transition from a paraepidermal organization to a mature periepidermal Hartig net after 15 d of contact. Using a standard fungal growth medium, formation and development of mycorrhizas were not greatly affected by changes in the overall concentrations of nitrogen and phosphorus but changes in the ratio of nitrogen to phosphorus had strong effects on development and mycorrhiza formation was completely suppressed when the ratio of nitrogen to phosphorus was increased. These differences were not related to the effects of nitrogen or phosphorus on linear growth of the fungus.
|
|
| 8. |
- Bösch, Yvonne, et al.
(författare)
-
Minimizing tillage modifies fungal denitrifier communities, increases denitrification rates and enhances the genetic potential for fungal, relative to bacterial, denitrification
- 2022
-
Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 170
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrous oxide (N2O) emissions from arable soils are predominantly caused by denitrifying microbes, of which fungal denitrifiers are of particular interest, as fungi, in contrast to bacteria, terminate denitrification with N2O. Reduced tillage has been shown to increase gaseous nitrogen losses from soil, but knowledge of how varying tillage regimes and associated soil physical and chemical alterations affect fungal denitrifiers is limited. Based on results from a long-term (>40 years) tillage experiment, we show that non-inversion tillage resulted in increased potential denitrification activity in the upper soil layers, compared to annual or occasional (every 4-5 years) conventional inversion tillage. Using sequence-corrected abundance of the fungal nirK gene, we further identified an increased genetic potential for fungal denitrification, compared to that caused by bacteria, with decreasing tillage intensity. Differences in the composition and diversity of the fungal nirK community imply that different tillage regimes select for distinct fungal denitrifiers with differing functional capabilities and lifestyles, predominantly by altering carbon and nitrogen related niches. Our findings suggest that the creation of organic hotspots through stratification by non-inversion tillage increases the diversity and abundance of fungal denitrifier communities and modifies their composition, and thus their overall relevance for N2O production by denitrification, in arable soils.
|
|
| 9. |
- Chalot, Michel, et al.
(författare)
-
Factors affecting amino-acid-uptake by the ectomycorrhizal fungus Paxillus involutus
- 1995
-
Ingår i: Mycological Research. - 0953-7562. ; 99:9, s. 1131-1138
-
Tidskriftsartikel (refereegranskat)abstract
- Factors affecting amino acid uptake by the ectomycorrhizal fungus Paxillus involutus were investigated using tracer kinetic experiments. Amino acid uptake by P. involutus was dependent on the pH of the incubation medium. Uptake of L-glutamate and L-glutamine had a distinct pH optimum around pH 4.0 and declined sharply between pH 4.5 and 6.4. Uptake of alanine and aspartate was also highest at low pH values (3-4) but declined more slowly with increasing pH. Total uptake of labelled amino acids was unaffected by 0.05 or 0.5 mM ammonium while 5 mM ammonium decreased amino acid uptake. Nitrate or glucose did not significantly affect amino acid uptake but glucose greatly increased the proportion of carbon that was respired. Uptake of the different amino acids decreased by a factor of 4 to 10 with increasing age (1-5 wk) and the proportion of absorbed C-14 that was respired increased with age. Changes in the size of the total amino acid pool were inversely related to those in the rate of uptake and the pool increased steadily with age. The implications of the ability of P. involutus to take up amino acids are discussed.
|
|
| 10. |
- Chalot, Mickel, et al.
(författare)
-
Metabolism of [C-14] glutamate and [C-14] glutamine by the ectomycorrhizal fungus Paxillus involutus
- 1994
-
Ingår i: Microbiology. - : Microbiology Society. - 1465-2080 .- 1350-0872. ; 140, s. 1641-1649
-
Tidskriftsartikel (refereegranskat)abstract
- To examine pathways of glutamate and glutamine metabolism in the ectomycorrhizal fungus Paxillus involutus, tracer kinetic experiments were performed using L-[U-C-14]glutamate and L-[U-C-14]glutamine and the enzyme inhibitors methionine sulfoximine (MSX), azaserine (AZA) and aminooxyacetate (AOA). When [C-14]glutamate was supplied to fungal cultures, 25% of the radioactivity of the amino acid fraction was incorporated into glutamine after 5 min feeding, but MSX inhibited incorporation of C-14 into glutamine by 85%, suggesting the rapid operation of glutamine synthetase. Conversely, when P. involutus was fed with [C-14]glutamine, 46% of the label was found in glutamate within 30 min of feeding and AZA inhibited glutamate formation by 90%. Taken together, these data indicate that glutamate synthase (GOGAT) is the major enzyme of glutamine degradation. In addition, the strong inhibition of glutamine utilization by AOA indicates that glutamine catabolism in P. involutus might involve a transamination process as an alternative pathway to GOCAT for glutamine degradation. The high (CO2)-C-14 evolution shows that glutamate and glutamine are further actively consumed as respiratory substrates, being channelled through the tricarboxylic acid (TCA) cycle and oxidized as CO2. It appears that synthesis of amino acid precursors during TCA cycle operation is an essential step far aspartate and alanine synthesis through aminotransferase activities in P. involutus.
|
|
