| 1. |
- Bahr, Adam
(författare)
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Ectomycorrhizal fungi: Their role in nitrogen retention and carbon sequestration in northern coniferous forests
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Almost all northern forest tree species live in symbioses with ectomycorrhizal fungi (EMF). The trees allocate up to half of the photoassimilated carbon (C) through the roots to EMF. In return EMF deliver nutrients from both inorganic and organic sources in the soil, as well as water. Most of the nutrients trees need are assimilated through EMF, which thus play a potentially important role in retaining nitrogen (N) in the soil. However, it is still not clear to what extent they contribute to the total N retention capacity of northern forest soils. This thesis shows that recently produced (within 4 months) mycelium of EMF was capable to assimilate a substantial amount of inorganic N (6 kg-1 ha-1 month-1). If the total standing biomass of EMF mycelium where to be taken in to account, the total EMF N assimilation would likely be much larger. On the other hand, an abundant network of EMF mycelium was not sufficient to prevent a flush of N leaching that followed immediately after N fertilization, but it may be sufficient to retain more moderate additions of N. Leaching of N has been reported in N saturated northern forests, and further research is needed to reveal the role of N retention by EMF in relation to N assimilation by other microorganisms or directly by the tree roots, under various levels of N input in forest soil. Northern forest soils have been reported as a major terrestrial C pool. This is typically explained by slow decomposition due to low temperatures, and recalcitrant litter from the coniferous trees that dominate these forests. A less discussed source to the C pool is the one originating from roots and root associated microorganisms. Since about half of the photoassimilated C is allocated belowground in coniferous forests, this is a potentially important process affecting the C sequestration. Previous studies have highlighted the potential of EMF as an important contributor to C sequestration. This is based on observations of substantial production of EMF mycelium, and that EMF tissue contains recalcitrant compounds. One of the conclusions in this thesis was that most of the soil organic C (SOC) in late successional stages originates from belowground inputs from roots and root associated fungi. This contrasts the focus on aboveground plant production in other studies where changes in forest C storage have been examined. Other results emphasize the important role of EMF in the build-up of soil organic matter: up to more than half a ton of EMF mycelium was produced during only four months, and the average C sequestration by EMF mycelium in a large scale field survey was calculated to more than 300 kg C ha-1 y-1. Carbon sequestered by EMF may however be sensitive to additions of N, which typically repress EMF growth. There have been many observations of reduced EMF mycelium production after large additions of inorganic N (typically 100 kg-1 ha-1 y-1), but we show that the moderate (less than 20 kg-1 ha-1 y-1) and continuous addition from elevated N deposition in many northern forest regions is sufficient for the repressive effect to occur. Consequently, C sequestration by EMF may be reduced by N deposition. This opposes the positive effect that N addition has on C sequestration due to other processes that are based on aboveground C inputs and degradation of soil organic matter. Even though previous research indisputably show that large N additions increase the C sequestration in forest soils, the effect is lacking at moderate N inputs. Thus, an important question that still remains to be answered is how low levels of anthropogenic N deposition affect the C cycle in northern forest regions. Further, the belowground contribution to SOC is often neglected, but necessary to include for accurate modeling of the C cycle in northern forests, particularly given the evidence that belowground inputs can make a larger contribution to SOC than aboveground inputs.
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| 2. |
- Bahr, Adam, et al.
(författare)
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Growth of ectomycorrhizal fungal mycelium along a Norway spruce forest nitrogen deposition gradient and its effect on nitrogen leakage
- 2013
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 59, s. 38-48
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Tidskriftsartikel (refereegranskat)abstract
- Almost all boreal and temperate forest tree species live in symbiosis with ectomycorrhizal fungi (EMF); the trees transfer carbon (C) to the fungi in exchange for nutrients and water. Several studies have shown that experimental application of inorganic nitrogen (N) represses production of EMF extramatrical mycelia (EMM), but studies along N deposition gradients are underrepresented. Other environmental variables than N may influence EMM production and in this study we included 29 thoroughly monitored Norway spruce stands from a large geographical region in Sweden in order to evaluate the importance of N deposition on EMM growth and N leaching in a broader context. It was concluded that N deposition was the most important factor controlling EMM production and that the amounts typically deposited in boreal and boreo-nemoral regions can be sufficient to reduce EMM growth. Other factors, such as phosphorus status and pH, were also correlated with EMM production and should be considered when predicting EMM growth and N leaching. We also showed that EMM production substantially contributed to the C sequestration (320 kg ha(-1) yr(-1)), suggesting that it should be included in C cycle modelling. Furthermore, EMF are probably important for the N retention capacity since high N leaching coincided with low EMM growth. However, it was not possible to differentiate between the effects of EMF and the direct effect of N deposition on N leaching in the present study.
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| 3. |
- Bahr, Adam, et al.
(författare)
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Long-term changes in vegetation and soil chemistry in a calcareous and sandy semi-natural grassland
- 2012
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Ingår i: Flora: Morphology, Distribution, Functional Ecology of Plants. - : Elsevier BV. - 0367-2530. ; 207:5, s. 379-387
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Tidskriftsartikel (refereegranskat)abstract
- Calcicole plant species are vulnerable to acidification and fertilization, caused by deposition and changes in land use, since they are adapted to nutrient-poor calcareous conditions. In this study we used vegetation data (vascular plants, bryophytes and lichens) from 1964 and 1985 and stored soil samples from 1966 to investigate long-term soil chemistry and vegetation changes in a semi-natural, sandy calcareous grassland in southern Sweden. In the re-investigation in 2008 we found that increased decalcification due to acidification could not be verified. The plant community had changed from stress-tolerant calcareous grassland towards a community promoted by higher nutrient availability. Furthermore, the cover of species indicating calcareous conditions had decreased. A decline in the cover of species adapted to alkaline, phosphorus-poor conditions may be due to increased nutrient availability, but there were also indications that the vegetation had changed due to overgrowth by woody plants. This long-term impoverishment of the plant community highlights the need for appropriate management of calcareous grasslands, in order to limit the nutrients available in the soil and prevent overgrowth by shrubs and trees. (C) 2012 Published by Elsevier GmbH.
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| 4. |
- Bahr, Adam, et al.
(författare)
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Nitrogen leaching and ectomycorrhizal nitrogen retention capacity in a Norway spruce forest fertilized with nitrogen and phosphorus
- 2015
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 390:1-2, s. 323-335
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Tidskriftsartikel (refereegranskat)abstract
- To estimate the production of external ectomycorrhizal mycelia (EMM) in Norway spruce forests with varying nitrogen (N) and phosphorus (P) levels, and to relate this to the N retention capacity of ectomycorrhizal fungi (EMF) and N leaching. Seasonal changes in EMF production (in ingrowth mesh bags) and soil water N (in suction lysimeters) were analyzed after fertilization with N or N combined with P. The EMF N retention capacity was estimated by the addition of isotopically labeled N to the mesh bags. No relationship was found between the seasonal variation in EMF growth and N leakage from the soil. However, in the mesh bags, the total assimilation of N-15 by EMF was almost halved by N fertilization, while twice as much N-15 leached through. We found a high specific N assimilation capacity per unit weight of EMF mycelia. This was unaffected by N fertilization, but the total assimilation of N by EMF was drastically reduced due to reduced production of EMM. However, N-retaining processes other than N assimilation by EMF must be taken into account to explain the losses of N after fertilization.
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| 5. |
- Ekblad, Alf, et al.
(författare)
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Production and turnover of ectomycorrhizal extramatrical mycelial biomass and necromass under elevated CO2 and nitrogen fertilization
- 2016
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Ingår i: New Phytologist. - Hoboken, USA : Wiley. - 0028-646X .- 1469-8137. ; 211:3, s. 874-885
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Tidskriftsartikel (refereegranskat)abstract
- Extramatrical mycelia (EMM) of ectomycorrhizal fungi are important in carbon (C) and nitrogen (N) cycling in forests, but poor knowledge about EMM biomass and necromass turnovers makes the quantification of their role problematic. We studied the impacts of elevated CO2 and N fertilization on EMM production and turnover in a Pinus taeda forest. EMM C was determined by the analysis of ergosterol (biomass), chitin (total bio- and necromass) and total organic C (TOC) of sand-filled mycelium in-growth bags. The production and turnover of EMM bio- and necromass and total C were estimated by modelling. N fertilization reduced the standing EMM biomass C to 57% and its production to 51% of the control (from 238 to 122 kg C ha-1 yr-1), whereas elevated CO2 had no detectable effects. Biomass turnover was high (~13 yr-1) and unchanged by the treatments. Necromass turnover was slow and was reduced from 1.5 yr-1 in the control to 0.65 yr-1 in the N-fertilized treatment. However, TOC data did not support an N effect on necromass turnover. An estimated EMM production ranging from 2.5 to 6% of net primary production stresses the importance of its inclusion in C models. A slow EMM necromass turnover indicates an importance in building up forest humus.
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| 6. |
- Engelbrecht Clemmensen, Karina, et al.
(författare)
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Roots and associated fungi drive long-term carbon sequestration in boreal forest
- 2013
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 339:6127, s. 1615-1618
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Tidskriftsartikel (refereegranskat)abstract
- Boreal forest soils function as a terrestrial net sink in the global carbon cycle. The prevailing dogma has focused on aboveground plant litter as a principal source of soil organic matter. Using C-14 bomb-carbon modeling, we show that 50 to 70% of stored carbon in a chronosequence of boreal forested islands derives from roots and root-associated microorganisms. Fungal biomarkers indicate impaired degradation and preservation of fungal residues in late successional forests. Furthermore, 454 pyrosequencing of molecular barcodes, in conjunction with stable isotope analyses, highlights root-associated fungi as important regulators of ecosystem carbon dynamics. Our results suggest an alternative mechanism for the accumulation of organic matter in boreal forests during succession in the long-term absence of disturbance.
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| 7. |
- Nicolás, César, et al.
(författare)
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Chemical changes in organic matter after fungal colonization in a nitrogen fertilized and unfertilized Norway spruce forest
- 2017
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 419:1-2, s. 113-126
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims: Decomposition and transformation of organic matter (OM) in forest soils are conducted by the concomitant action of saprotrophic and mycorrhizal fungi. Here, we examine chemical changes in OM after fungal colonization in nitrogen fertilized and unfertilized soils from a Norway spruce forest. Methods: Sand-filled bags amended with composted maize leaves were placed in the forest soil and harvested after 17 months. Infrared and near edge X-ray absorption fine structure spectroscopies were used to study the chemical changes in the OM. Fungal community composition of the bags was also evaluated. Results: The proportion of ectomycorrhizal fungi declined in the fertilized plots, but the overall fungal community composition was similar between N treatments. Decomposition of the OM was, independently of the N level or soil horizon, accompanied by an increase of C/N ratio of the mesh-bag content. Moreover, the proportions of carboxylic compounds in the incubated OM increased in the mineral horizon, while heterocyclic-N compounds decreased, especially in unfertilized plots with higher N demand from the trees. Conclusions: Our results indicate that more oxidized organic C and less heterocyclic-N proportions in the OM remain after fungal colonization in the mineral layers, and suggest that ectomycorrhizal fungi transfer less heterocyclic-N from the mesh bags to the host trees under high N levels.
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| 8. |
- Rio, Ebonie Kendra, et al.
(författare)
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ICON PART-T 2019-International Scientific Tendinopathy Symposium Consensus : recommended standards for reporting participant characteristics in tendinopathy research (PART-T)
- 2020
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Ingår i: British Journal of Sports Medicine. - : BMJ Publishing Group Ltd. - 0306-3674 .- 1473-0480. ; 54:11, s. 627-630
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Tidskriftsartikel (refereegranskat)abstract
- We aimed to establish consensus for reporting recommendations relating to participant characteristics in tendon research. A scoping literature review of tendinopathy studies (Achilles, patellar, hamstring, gluteal and elbow) was followed by an online survey and face-to-face consensus meeting with expert healthcare professionals (HCPs) at the International Scientific Tendon Symposium, Groningen 2018. We reviewed 263 papers to form statements for consensus and invited 30 HCPs from different disciplines and geographical locations; 28 completed the survey and 15 attended the meeting. There was consensus that the following data should be reported for cases and controls: sex, age, standing height, body mass, history of tendinopathy, whether imaging was used to confirm pathology, loading tests, pain location, symptom duration and severity, level of disability, comorbidities, physical activity level, recruitment source and strategies, and medication use history. Standardised reporting of participant characteristics aims to benefit patients and clinicians by guiding researchers in the conduct of their studies. We provide free resources to facilitate researchers adopting our recommendations.
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| 9. |
- Rousk, Johannes, et al.
(författare)
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Examining the fungal and bacterial niche overlap using selective inhibitors in soil.
- 2008
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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 63:3, s. 350-358
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Tidskriftsartikel (refereegranskat)abstract
- It is important to know the contributions of bacteria and fungi to decomposition in connection with both the structure of the food web and the functioning of the ecosystem. However, the extent of the competition between these groups of organisms is largely unknown. The bacterial influence on fungal growth in a soil system was studied by applying three different bacterial inhibitors - bronopol, tylosin and oxytetracycline - in a series of increasing concentrations, and comparing the resulting bacterial and fungal growth rates measured using leucine and acetate-in-ergosterol incorporation, respectively. Direct measurements of growth showed that fungi increased after adding inhibitors; the level of increase in fungal growth corresponded to that of the decrease in bacterial growth, irrespective of the bacterial inhibitor used. Similar antagonistic effects of the bacteria on fungal growth were also found after adding the bacterial inhibitors together with additional substrate (alfalfa or straw plant material). The resulting responses in bacterial and fungal growth indirectly indicated that the negative interaction between fungi and bacteria was mostly attributable to exploitation competition. The results of this study also emphasize the increased sensitivity of using growth-related, instead of biomass-based, measurements when studying bacterial and fungal interactions in soil.
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| 10. |
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