| 1. |
- Aliasgharzad, Nasser, et al.
(författare)
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Acidification of a sandy grassland favours bacteria and disfavours fungal saprotrophs as estimated by fatty acid profiling
- 2010
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:7, s. 1058-1064
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the structure of a microbial community in semi-natural sandy grassland in southeast Sweden. The sand is rich in lime, but in most places the soil is decalcified in the upper layers, and therefore this site shows a large variation in pH within short distances. We collected samples at three different soil depths (0-10 cm, 10-20 cm and 20-30 cm) and found the pH to range from 5 to 8 in the topsoil and from 4.5 to 9.5 in the deepest layer. The abundance of saprophytic fungi and bacteria was investigated using signature phospholipid fatty acids and arbuscular mycorrhizal fungi (AMF) using the neutral lipid fatty acid 16:1 omega 5. The PLFA pattern of the topsoil was different from that in the other two layers, as indicated by principal component analysis. The saprotrophic fungi were associated with high pH, and bacteria with low pH in these sandy soils. No relation was found between pH and AMF in the topsoil, while a positive relation was found in the deepest soil layer. The saprophytic fungi-to-bacteria ratio was constant with depth, while the AMF-to-bacteria ratio increased with soil depth. The results showed that high soil pH favoured fungal saprophytes in sandy grasslands and that AMF are relatively more abundant than the other two groups in deeper soil layers: particularly so when the pH is high. (C) 2010 Elsevier Ltd. All rights reserved.
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| 2. |
- Aliasgharzad, Nasser, et al.
(författare)
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Lack of arbuscular mycorrhizal colonisation in tea (Camellia sinensis L.) plants cultivated in Northern Iran
- 2011
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Ingår i: Symbiosis. - : Springer Science and Business Media LLC. - 0334-5114 .- 1878-7665. ; 55:2, s. 91-95
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Tidskriftsartikel (refereegranskat)abstract
- Soil and roots associated with different tea clones and nearby weeds (Veronica sp., Setaria sp., Salvia sp., Senecio sp. and Tripogon sp.) were sampled for arbuscular mycorrhizal fungi (AMF) in the tea gardens of Northern Iran. Spores were searched for in the soil and AMF colonisation determined microscopically and fatty acid signatures in roots was determined. Root samples from mycorrhizal and non-mycorrhizal clover were used as positive and negative controls. AMF spores were abundant in the tea garden soils; the genera Glomus and Acaulospora dominated. Microscopic observations of stained tea roots showed no sign of AMF. To confirm this, the roots were analysed for fatty acid signature compounds. The average level of PLFA 16:1 omega 5 as signature molecule for AMF in tea roots was 2 nmol g(-1) dry root, while the NLFA 16: 1 omega 5 was not detectable. In mycorrhizal and non-mycorrhizal clover roots, the PLFA 16:1 omega 5 was 141 and 5.74 nmol g(-1) dry root, respectively. In roots of weeds in tea plantations, the amount of PLFA 16:1 omega 5 was in the range 4.9 to 31.1 nmol g(-1) dry root. Thus, there was no evidence for AMF association in tea roots and weeds are thought to be the source of the spores in the soils. Finally, no mycorrhizal colonisation was found when tea plant seedlings were inoculated with AMF in pot cultures.
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| 3. |
- Antonsen, H, et al.
(författare)
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Relative importance of burning, mowing and species translocation in the restoration of a former boreal hayfield: responses of plant diversity and the microbial community
- 2005
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Ingår i: Journal of Applied Ecology. - : Wiley. - 1365-2664 .- 0021-8901. ; 42:2, s. 337-347
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Tidskriftsartikel (refereegranskat)abstract
- 1. The extensive loss of species-rich grasslands in Europe as a result of agricultural intensification has triggered a desire to recreate more diverse and natural grassland systems in set-aside fields. Appropriate management and species introductions are necessary to overcome residual soil fertility, lack of suitable plant propagules and dominance of undesirable invasive species. 2. A field experiment was performed in a boreal former hayfield to test the effect of turf inoculation, mowing (twice annually) and spring burning. We surveyed changes in plant diversity, composition and productivity over a 3-year period. Signature fatty acids and soil respiration measurements were employed to survey changes in the soil community. 3. Few changes in the vegetation and soil communities could be related to inoculation of turf monoliths. Most of the measured variables in mown plots differed from the set-aside (control) plots, while burned plots displayed mainly similar responses. Mowing increased plant species richness and diversity, mainly by enhancing the number and frequency of forb species. Small-statured forb species were promoted by mowing, whereas tall leafy grasses declined. Effects of mowing on soil communities comprised an increased soil respiration and stimulation of arbuscular mycorrhizal fungi. 4. Synthesis and applications. The results demonstrate the importance of reducing sward height in order to promote plant species coexistence in former boreal hayfields. In such systems, eliminating accumulated litter by spring burning has little influence on species composition when the sward is allowed to grow tall. Mowing is therefore the most efficient way of enhancing biodiversity. The results also show that mowing-mediated changes in above-ground plant communities may stimulate below-ground symbiotic micro-organisms, potentially resulting in a positive feedback on ecosystem development.
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| 4. |
- 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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| 5. |
- Bahram, Mohammad, et al.
(författare)
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Structure and function of the global topsoil microbiome
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 560:7717, s. 233-7
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Tidskriftsartikel (refereegranskat)abstract
- Soils harbour some of the most diverse microbiomes on Earth and are essential for both nutrient cycling and carbon storage. To understand soil functioning, it is necessary to model the global distribution patterns and functional gene repertoires of soil microorganisms, as well as the biotic and environmental associations between the diversity and structure of both bacterial and fungal soil communities(1-4). Here we show, by leveraging metagenomics and metabarcoding of global topsoil samples (189 sites, 7,560 subsamples), that bacterial, but not fungal, genetic diversity is highest in temperate habitats and that microbial gene composition varies more strongly with environmental variables than with geographic distance. We demonstrate that fungi and bacteria show global niche differentiation that is associated with contrasting diversity responses to precipitation and soil pH. Furthermore, we provide evidence for strong bacterial-fungal antagonism, inferred from antibiotic-resistance genes, in topsoil and ocean habitats, indicating the substantial role of biotic interactions in shaping microbial communities. Our results suggest that both competition and environmental filtering affect the abundance, composition and encoded gene functions of bacterial and fungal communities, indicating that the relative contributions of these microorganisms to global nutrient cycling varies spatially.
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| 6. |
- Bao, Xiaozhe, et al.
(författare)
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Arbuscular mycorrhiza under water — Carbon‒phosphorus exchange between rice and arbuscular mycorrhizal fungi under different flooding regimes
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 129, s. 169-177
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Tidskriftsartikel (refereegranskat)abstract
- Arbuscular mycorrhizal fungi (AMF) are commonly present in wetlands, but their functional role there is not well understood. We have quantified the carbon (C) allocation from rice to AMF under different flooding regimes, using stable isotope labeling (13CO2), and assessed the potential phosphorus (P) delivery from AMF to rice by profiling the expression of plant and fungal P transporter genes. The results showed that the plant-assimilated C was allocated to AMF under all flooding regimes, as evidenced by the significant enrichment of 13C in the AMF signature fatty acids. The plant C allocation to AMF declined at increased flooding intensity, and was strikingly greater at the growth stage when the rice plants had a higher nutrient requirement. The gene expression profiles and rice P levels strongly indicated that a considerable amount of P was transported to plants via the mycorrhizal pathway under wetland conditions, although AMF colonization did not improve rice growth. This work provides the first solid evidence of C‒P exchange in AM symbiosis under flooded conditions, although it is reduced compared to non-flooded conditions. Nonetheless, this means that AMF may have an important function in wetlands, which opens new perspectives on the application of symbiotic AMF in wetlands.
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| 7. |
- Barceló, Milagros, et al.
(författare)
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Mycorrhizal tree impacts on topsoil biogeochemical properties in tropical forests
- 2022
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 110:6, s. 1271-1282
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Tidskriftsartikel (refereegranskat)abstract
- In tropical regions, the patterns of carbon (C) and nutrient properties among ecosystems dominated by distinct mycorrhizal associations are unknown. We aim to reveal whether the dynamics differ and the ecological drivers and ecosystem functioning implications of such differences. Based on a dataset of 97 tropical forest sites, we related EcM trees abundance (as a proxy for the transition from AM to EcM trees dominance) to different topsoil properties, climatic conditions and microbial abundance proxies through Generalized Additive Models. Higher abundances of EcM trees were correlated with higher topsoil concentrations of total nitrogen and C, extractable phosphorus and potassium, δ13C, mean annual temperature, precipitation, microbial (bacterial and fungal) biomass and the relative abundance of saprotrophic fungi. Synthesis. Our results reveal consistent differences in carbon and nutrient content between arbuscular mycorrhizal (AM-) and EcM-dominated vegetation across the tropical biome, pointing to lower soil fertility and lower rates of C and nutrient transformation processes in EcM-dominated forests. These patterns associate with lower topsoil C accumulation when compared to AM vegetation, which contrasts with patterns reported for temperate forests. We suggest that different mechanisms of soil organic matter accumulation explain the contrasting impacts of EcM dominance on topsoil properties of temperate and tropical biomes. Global vegetation and C models should account for the contrasting impacts of distinct mycorrhizal vegetation in different climatic zones.
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| 8. |
- Barin, Mohsen, et al.
(författare)
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Abundance of arbuscular mycorrhizal fungi in relation to soil salinity around Lake Urmia in northern Iran analyzed by use of lipid biomarkers and microscopy
- 2013
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Ingår i: Pedobiologia. - : Elsevier BV. - 1873-1511 .- 0031-4056. ; 56:4-6, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- Saline soils around Lake Urmia in northern Iran constitute a stressed environment for plants and microbial communities, including arbuscular mycorrhizal (AM) fungi. Soil and root samples were collected from fields cultivated with the glycophytes Allium cepa L. and Medicago sativa L, and sites dominated by the halophyte Salicornia europaea L. Soil and root samples were analyzed for the AM fungal signature neutral lipid fatty acid (NLFA) 16:1 omega 5. The roots were also examined microscopically for mycorrhizal colonization. Each plant species was sampled across a salt gradient. Microscopic examination showed no AM fungal structures in the roots of S. europaea. The highest root colonization was recorded for M. sativa. The highest NLFA 16:1 omega 5 values were found in soil around M. sativa roots and the lowest in soil around S. europaea roots. We found evidence for stimulation of vesicle formation at moderate salinity levels in M. sativa, which is an indication of increased carbon allocation to mycorrhiza. On the other hand, we found a negative correlation between salinity and arbuscule formation in A. cepa, which may indicate a less functional symbiosis in saline soils. (C) 2013 Elsevier GmbH. All rights reserved.
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| 9. |
- Birgander, Johanna, et al.
(författare)
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Comparison of fertility and seasonal effects on grassland microbial communities
- 2014
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 76, s. 80-89
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Tidskriftsartikel (refereegranskat)abstract
- The activity of saprotrophic fungi and bacteria, and the balance between them, can affect decomposition. Arbuscular mycorrhizal (AM) fungi are also important for the nutrient and energy transfer in soil. Microbial community composition and activity are believed to have seasonal patterns, and are known to be highly influenced by environmental factors such as pH and nutrient conditions. To evaluate the importance of season for the variation in microbial decomposer community in a context of well-known environmental factor variation, we studied microbial growth, biomass and community structure along a fertility gradient (pH 5.9-8.1; NH4-N 3-19 mu g g(-1) soil, f.w.) in a sandy grassland during one year. The microbial community structure (phospholipid fatty acid (PLFA) composition) and biomass (PLFA and neutral lipid fatty acid (NLFA) signatures) as well as fungal (acetate incorporation in ergosterol) and bacterial (leucine incorporation) growth rates were investigated at eight seasonal time points during one year. The environmental factors pH and NH4 concentrations explained a larger share of the variation in the microbial community structure. Together they explained 37% of the variation, while season (proxied by temperature) only explained 6% of the variation in PLFA composition. Bacterial and fungal biomass were both highest in early spring, while AM fungal biomass peaked in early summer. Bacterial growth rate, on the other hand, was highest during the autumn, while fungal growth rate showed no clear seasonal pattern. In conclusion, the influence of seasonal variation on microbial communities proved to be relatively small compared to that which could be assigned to pH and NH4 in the studied ranges. (C) 2014 Elsevier Ltd. All rights reserved.
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| 10. |
- Birgander, Johanna, et al.
(författare)
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The responses of microbial temperature relationships to seasonal change and winter warming in a temperate grassland
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 24:8, s. 3357-3367
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Tidskriftsartikel (refereegranskat)abstract
- Microorganisms dominate the decomposition of organic matter and their activities are strongly influenced by temperature. As the carbon (C) flux from soil to the atmosphere due to microbial activity is substantial, understanding temperature relationships of microbial processes is critical. It has been shown that microbial temperature relationships in soil correlate with the climate, and microorganisms in field experiments become more warm-tolerant in response to chronic warming. It is also known that microbial temperature relationships reflect the seasons in aquatic ecosystems, but to date this has not been investigated in soil. Although climate change predictions suggest that temperatures will be mostly affected during winter in temperate ecosystems, no assessments exist of the responses of microbial temperature relationships to winter warming. We investigated the responses of the temperature relationships of bacterial growth, fungal growth, and respiration in a temperate grassland to seasonal change, and to 2 years’ winter warming. The warming treatments increased winter soil temperatures by 5–6°C, corresponding to 3°C warming of the mean annual temperature. Microbial temperature relationships and temperature sensitivities (Q10) could be accurately established, but did not respond to winter warming or to seasonal temperature change, despite significant shifts in the microbial community structure. The lack of response to winter warming that we demonstrate, and the strong response to chronic warming treatments previously shown, together suggest that it is the peak annual soil temperature that influences the microbial temperature relationships, and that temperatures during colder seasons will have little impact. Thus, mean annual temperatures are poor predictors for microbial temperature relationships. Instead, the intensity of summer heat-spells in temperate systems is likely to shape the microbial temperature relationships that govern the soil-atmosphere C exchange.
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