| 1. |
- Ayuke, Fredrick, et al.
(author)
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Effects of biocontrol bacteria and earthworms on the severity of Alternaria brassicae disease and the growth of oilseed rape plants (Brassica napus)
- 2017
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 117-118, s. 63-69
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Journal article (peer-reviewed)abstract
- Biological control of plant diseases through the addition of microbial biocontrol agents and the promotion of earthworms can be an environmentally friendly alternative to the chemical control of plant diseases. However, possible risks with biocontrol agents and their interactions with earthworms and other soil biota have not been well studied. The aim of this study was to assess whether the beneficial bacterium Bacillus amyloliquefaciens and the earthworms Aporrectodea caliginosa or Aporrectodea longa could reduce disease in oilseed rape (Brassica napus) challenged with the pathogen Alternaria brassicae. Plant growth and productivity were measured as plant survival, height, biomass, and flower development as well as disease index. A second objective was to assess whether the presence of the bacterium at high concentrations would influence the survival, growth, and reproduction of the earthworms. One outdoor and one greenhouse experiment were performed with Br. napus plants challenged with AL brassicae inoculated to the plant leaves in the presence or absence of Bacillus amyloliquefaciens inoculated to the root environment and in the presence or absence of earthworms (Ap. caliginosa or Ap. longa) added to the soil. All treatments were replicated three times. In the outdoor experiment, inoculation with AL brassicae reduced the growth of plants and the addition of Ap. caliginosa increased plant height. In the greenhouse experiment, pairwise comparisons of plants challenged with AL brassicae showed that treatment with B. amyloliquefaciens led to significantly lower disease index than the treatment with Ap. caliginosa plus B. amyloliquefaciens, while other treatments had intermediate disease indices. The addition of AL brassicae or B. amyloliquefaciens increased the survival and mass increment of Ap. caliginosa as a main effect when used separately but not when used in combination.This study did not give any clear indication of the usefulness of B. amyloliquefaciens for biocontrol of plant pathogens such as AL brassicae when growing plants in natural soil. In addition, no significantly positive effects from the tested earthworm species were seen.
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| 2. |
- Bargaz, Adnane, et al.
(author)
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Species interactions enhance root allocation, microbial diversity and P acquisition in intercropped wheat and soybean under P deficiency
- 2017
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 120, s. 179-188
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Journal article (peer-reviewed)abstract
- Belowground interactions in grain legume-cereal intercrops may improve resource acquisition and adaptation to environmental constraints such as phosphorus (P) deficiency. To advance the knowledge of belowground facilitative mechanisms involved in P-deficiency tolerance (root allocation, biochemical and microbial responses), soybean (Glycine max) and wheat (Triticum aestivum) were grown as monocrops and intercrops under P-deficiency and P-sufficiency conditions in soil-filled rhizoboxes. The hypothesis was that intercropping stimulates root microbial diversity, root biomass allocation and P-hydrolyzing acid phosphatases (APase) activity in roots under P-deficient conditions. Total root dry weight (RDW), length, and surface area significantly increased in P-deficient intercropped wheat and soybean. Greater root allocation to deeper soil layers was evident for P-deficient intercropped wheat. Shallow roots of intercropped wheat exhibited highly stimulated APase activity under P-deficient conditions while shallow roots of monocropped soybean exhibited higher APase activity in comparison to deeper roots, irrespective of P treatment. Root fungal diversity was significantly (p < 0.05) higher in intercropped wheat, and was significantly correlated with RDW, root APase activity, shoot P, and soil available P (rho = 0.24, p= 0.01). Root bacterial diversity was higher in both intercrops, and was significantly correlated with RDW and shoot N concentration. The observed shifts in root microbial diversity, root biomass allocation and APase activity provide explanatory mechanisms of relationships between rhizosphere heterogeneity and pathways for increased P acquisition in diversified crops. Advanced belowground metabolomics on root microbial communities are required to reveal the beneficial effect of root microorganisms in associations of different crop species.
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| 3. |
- Bengtsson, Jan
(author)
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The response of springtails to fire in the fynbos of the Western Cape, South Africa
- 2016
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 108, s. 165-175
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Journal article (peer-reviewed)abstract
- Although fire is a natural form of disturbance in many ecosystems, the frequency of fires is increasing due to human activities. Hence, understanding the impacts of fire on biodiversity and ecosystem functioning has become increasingly important. In this study we investigated the effects of a large-scale fire on an important soil-dwelling group, springtails (Collembola), one year before and for three consecutive years after a fire in the fire-prone fynbos ecosystem in South Africa. In particular, we investigate the resistance of the springtail assemblages (i.e. their ability to remain relatively unchanged in the face of a disturbance), and their resilience (i.e. ability to return to a pre-disturbance state). To do this we sampled two sites with contrasting vegetation (Erica and Protea) and used three different standardized litter types in litterbag traps. A total of 35 springtail species from 31 genera and 14 families was found. The springtail assemblages in this fynbos system showed slightly more resistance to fire than resilience after the fire event, though substantial variation was found among vegetation types. Mean species richness and abundance per litterbag varied among the Protea and Erica sites, with resistant species being dominant in the Erica site, while species that showed an increase after the fire were dominant in the Protea site. Differences were also found between life forms: atmobiotic (free-living in vegetation) and epiedaphic (surface dwelling) species showed a significant decline in mean species richness directly after the fire in the Erica site. Euedaphic (soil-dwelling) species richness remained unchanged post-fire in the Erica site, while actually slightly increasing after the fire in the Protea site. Although the fynbos springtail assemblages had not fully recovered to pre-fire abundance after three years, many species appear to be resistant to or recover rapidly after fires, at least as ascertained over the relatively short (four years) duration of the study. It is likely that this response is influenced by the presence of suitable refugia within sites and by species-specific traits. Given changing fire regimes and the increasing frequency of fires due to human disturbances, the system will likely become more dominated by resistant springtail species preferring nutrient rich circumstances and easily decomposed litters. (C) 2016 Elsevier B.V. All rights reserved.
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| 4. |
- Björsell, Pia, et al.
(author)
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Interactions between some plant-parasitic nematodes and Rhizoctonia solani in potato fields
- 2017
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 113, s. 151-154
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Journal article (peer-reviewed)abstract
- The pathogenic fungus Rhizoctonia solani causes major economic losses for potato producers in Sweden. Producers, as well as extension officers, have reported possible increases in severity of R. solani when free-living plant-parasitic nematodes are present and active. The aim of this study was to investigate possible interactions and spatial correlations between root-lesion nematodes (Pratylenchus spp.), stubby-root nematodes (Trichodoridae) and the severity of stem canker caused by the fungus R. solani under field conditions. Nematodes in the genus' Globodera were also included after finding high numbers of these potato cyst nematode juveniles in the samples. Soil samples were taken in eight potato fields, located in the middle part of Sweden, with observed outbreaks of soil-borne stem canker caused by R. solani. Grading of stem canker and soil collections for nematode extraction were performed along transects starting from the centre of field patches with observed stem canker. There was no difference in the number of nematodes within the patches for any of the investigated nematode taxa, but the severity of stem canker was higher on plants graded in the centre of the patches compared to those graded in the margins. In addition, there was a spatial correlation between R. solani and stubby-root nematodes as well as potato cyst nematodes, but not for root-lesion nematodes. These results show that there is an interaction between plant-parasitic nematodes and R. solani in the field and this knowledge is of importance for future decisions of appropriate management methods. (C) 2017 The Authors. Published by Elsevier B.V.
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| 5. |
- Hydbom, Sofia, et al.
(author)
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Reduced tillage stimulated symbiotic fungi and microbial saprotrophs, but did not lead to a shift in the saprotrophic microorganism community structure
- 2017
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 119, s. 104-114
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Journal article (peer-reviewed)abstract
- The need for sustainable agricultural systems, which for example enhance soil organic carbon (SOC) content, has increased the interest for management with reduced tillage. In this study we used a Swedish long-term (20 yrs.) systems experiment, including reduced tillage (harrowing 10 cm) and plowing (moldboard plow 0–20 cm) combined with three levels of nitrogen (N) fertilization. With this setup we tested if (1) the arbuscular mycorrhizal fungi (AMF) concentration and (2) the fungi to bacteria (F:B) ratio would be higher under reduced tillage than under conventional tillage, and if this would be associated with higher SOC concentrations. We also tested if (3) the microbial biomass C close to the surface would be higher under reduced tillage than conventional tillage. Furthermore, since disturbance can reduce respiration and microbial growth we tested if (4) this occurred in our reduced tillage system. In addition, we tested if (5) fertilization increased the growth rate of fungi and decreased that of bacteria. We collected soil samples in July and October and found that the microbial biomass C, measured in October only, was higher close to the surface in the reduced tillage treatment and so was the microbial respiration. The fungal and bacterial growth rate, on the other hand, were not affected by tillage treatment. Fertilization did not affect the bacterial growth rate but did have a positive effect on fungal growth rate. In accordance with our expectations reduced tillage had a stimulating effect on AMF and saprotrophic fungi, and contrary to our expectation, also bacteria were positively affected by reduced tillage. In line with the unchanged F:B ratio, we found no indication that even 20 years of reduced tillage increased SOC concentrations in the long term.
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| 6. |
- Lagerlöf, Jan, et al.
(author)
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Potential side effects of biocontrol and plant-growth promoting Bacillus amyloliquefaciens bacteria on earthworms
- 2015
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 96, s. 159-164
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Journal article (peer-reviewed)abstract
- After 1-2 months, survival, growth and reproduction of the earthworms were recorded. We found no effect of the treatments as compared to control without BA amendments. We conclude that the use of high doses of BA with concentrations at the same magnitude as maximally expected when the bacteria are used as PGPR and BCA, is not harmful to the soil dwelling earthworms tested in this project. Further studies of the ecological effects of PGPR and BCA bacteria on other non-target soil organisms are encouraged. The development of sustainable agricultural systems, where ecosystem services are optimized, has to be aided by a deeper knowledge of the combined effect of bacteria and earthworms on the promotion of plant health. (C) 2015 Elsevier B.V. All rights reserved.
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| 7. |
- Löbmann, Michael, et al.
(author)
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The occurrence of pathogen suppressive soils in Sweden in relation soil biota, soil properties, and farming practices
- 2016
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 107, s. 57-65
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Journal article (peer-reviewed)abstract
- Despite more than 50 years of research and their great potential for sustainable pest management, pathogen suppressive soils remain poorly understood. We conducted a study on suppression of root rot disease symptoms associated with Pythium ultimum in untreated and heat-sterilized soil from ten southern Swedish farms with six different cropping and management regimes. Physical and chemical soil properties, soil nematodes belonging to different trophic guilds, and the predominant soil oomycetes were analyzed for their potential as indicators of soil suppressiveness. Six of the ten sampled soils were suppressive to P. ultimum disease symptoms. Suppressive or conducive properties of the soils from sites with permanent soil cover were related to the presence of live soil biota, while soils from sites with interrupted soil cover had suppressive or conducive effects unrelated to live soil biota. In soils with biologically conducive effects, soils had high or low cation nutrient content, while biologically suppressive soils had intermediate nutrient levels. No relationship was found between disease symptoms and the soil nematode trophic community or the predominant soil oomycetes. Permanent soil cover and a balanced nutrient supply were correlated with biologically suppressive effects on P. ultimum disease symptoms. (C) 2016 The Authors. Published by Elsevier B.V.
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| 8. |
- Malmström, Anna, et al.
(author)
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Why are forest fires generally neglected in soil fauna research? A mini-review
- 2016
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 98, s. 261-271
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Research review (peer-reviewed)abstract
- Climate change, unpredictable dry spells and human population growth are expected to increase the frequency of forest fires. Forest fires induce damage on soil ecosystems and seriously compromise their functionality and provision of ecosystem services. They reduce diversity in many soil organism groups, although they also support flora and fauna dependent on fires. Fires disrupt in the cycling of nutrients, and have been argued to threaten the sustainability of forest biomes. However, despite these potentially large effects on soil ecosystems, a literature survey on the forest fire effects on soil fauna demonstrated that the number of publications on this topic between 1979 and 2013 has been surprisingly low compared with studies of other kinds of disturbances. A poll conducted among soil ecologists who actually studied forest fires revealed that more than 50% of the findings about fire effects on soil ecosystems are unlikely to ever be published.The aim of this review was to discover and structure the reasons why forest fires are often neglected by soil zoologists and ecologists and to identify the major problems which deter soil zoologists from this area of research and from publishing obtained results. We show that forest fires are harder to study than many other types of disturbances. Fires are largely unpredictable and are often unique, which makes it difficult to apply statistically robust sampling plans and select proper controls. Spatial heterogeneity of fire intensity and soil fauna distribution complicate the resulting picture. Moreover, high variability of soil biota in time and space, and complicating effects of multiple fires make the results of such studies hard to interpret. We propose several approaches, which may help to document biodiversity and functional changes in soil communities affected by fire more effectively. These include prescribed burnings, indoor and outdoor experiments and meta-analyses of large datasets, including unpublished ones. We further justify the need for closer coordination of researchers to solve the "file drawer problem" for the unpublished data on soil biota shifts in response to forest fires. (C) 2015 Elsevier B.V. All rights reserved.
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| 9. |
- Pluchon, Nathalie, et al.
(author)
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The impact of charcoal and soil mixtures on decomposition and soil microbial communities in boreal forest
- 2016
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 99, s. 40-50
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Journal article (peer-reviewed)abstract
- Fire is a natural disturbance that operates as a major ecological driver in many ecosystems worldwide, and it produces charcoal which is incorporated into soil in significant quantities. Charcoal can serve as a long-term carbon (C) sink, but it is not inert, and could potentially impact native soil organic matter and decomposer micro-organisms. However, studies have shown contrasting results for how charcoal impacts the belowground subsystem, and the mechanisms involved are poorly understood, especially in pyrogenic ecosystems. We performed a laboratory experiment in which six contrasting boreal forest soil types and nine charcoal types (each from different woody plant species) were incubated for 9.5 months, both by themselves and in 50:50 mixtures for all possible soil-charcoal combinations. At harvest we measured mass loss, and for several charcoal-soil combinations, we measured microbial properties, and composition of C compounds using C-13 CP-MAS nuclear magnetic resonance (NMR) spectroscopy. Overall, mixtures of charcoal and soil lost more mass than expected based on when the components were incubated separately. The magnitude of increased soil mass loss in mixtures did not differ among charcoal types, but varied among soil types, because greater mass loss occurred when soil from a site dominated with herbaceous vegetation was used, relative to other soil types. The use of NMR spectroscopy showed that enhanced mass loss in mixtures was due mainly to mass loss of soil organic matter rather than charcoal. However, mixing of charcoal and soil did not influence key decomposer microbial groups compared with expected values derived from when components were incubated alone, irrespective of charcoal and soil type. This study shows that when charcoal is incorporated into boreal forest soil (e.g., after wildfire), there is enhanced loss of total C (arising primarily from mass loss of soil organic matter), with this effect being relatively consistent across contrasting charcoal and soil types. This effect, in combination with recently documented impacts of charcoal on aboveground processes, reveals important but largely overlooked legacy effects of charcoal on forest processes that contribute to ecosystem C balance and ecosystem functioning. (C) 2015 Elsevier B.V. All rights reserved.
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| 10. |
- Shahbaz, Muhammad
(author)
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Maize phenology alters the distribution of enzyme activities in soil: Field estimates
- 2018
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In: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 125, s. 233-239
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Journal article (peer-reviewed)abstract
- Microbial processes mediated by soil enzymes are crucial in soil organic matter decomposition, resulting in release of nutrients that become available for plant and microbial uptake. Therefore, it is crucial to know the sensitivity of enzyme activities (EA) along soil depths at distinct plant vegetation stages, and how the availability of mineral nitrogen (N) alters EA. We studied effects of N fertilization (0 and 160 kg N ha(-1)), soil depth (0-35 cm), and plant-phenological stage (silking and maturity) on microbial biomass C (C-mic) and potential activities of C-, N- and P-acquiring enzymes in the field under Zea mays L.Nitrogen fertilization increased shoot biomass by more than 80% compared to unfertilized plants. Maize roots triggered increases in Cmic and EA for all measured enzymes compared to bare fallow. Stimulating effect of plant roots on EA was enzyme specific and stronger at silking than maturity stage of maize. The down-regulating effect of N fertilization on EA involved in acquiring N was most pronounced on the activity of L-leucine aminopeptidase and beta-1,4-N-acetylglucosaminidase. Soil depth was the primary determinant of EA, explaining up to 51% of the variation. Depth-dependent EA changes were stronger in rooted soil.A pronounced biotic control on EA was demonstrated by higher EA in rooted soil than in bare fallow. This confirmed root-mediated microbial activation. Stronger effect of silking vs. maturity stage on EA indicated that actively growing roots fuel microorganisms via root-derived organics. Thus, soil depth and plant roots were major factors controlling microbial activity in arable soil.
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