| 1. |
- Rath, Kristin, et al.
(författare)
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Comparative toxicity of salts to microbial processes in soil.
- 2016
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 82:7, s. 2012-2020
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Tidskriftsartikel (refereegranskat)abstract
- Soil salinization is a growing threat to global agriculture and carbon (C) sequestration, but to date it remains unclear how microbial processes will respond. We studied the acute response to salt exposure of a range of anabolic and catabolic microbial processes, including bacterial (leucine incorporation) and fungal (acetate incorporation into ergosterol) growth rates, respiration and gross N mineralization and nitrification rates. To distinguish effects of specific ions from those of overall ionic strength, we compared the addition of four salts frequently associated with soil salinization (NaCl, KCl, Na2SO4, K2SO4) to a non-saline soil. To compare the tolerance of different microbial processes to salt, and to interrelate the toxicity of different salts, concentration-response relationships were established. Growth-based measurements revealed that fungi were more resistant to salt exposure than bacteria. Effects by salt on C and N mineralization were indistinguishable and, in contrast with previous studies, nitrification was not found to be more sensitive to salt exposure than other microbial processes. Ion specific toxicity of certain salts could only be observed for respiration, which was less inhibited by salts containing SO4 (2-) than Cl(-) salts, in contrast with the microbial growth assessments. This suggested that the inhibition of microbial growth was solely explained by total ionic strength, while ionic specific toxicity should also be considered for effects on microbial decomposition. This difference resulted in an apparent reduction of microbial growth efficiency in response to exposure to SO4 (2-) salts but not to Cl(-) salts; no evidence was found to distinguish K(+) and Na(+) salts.
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| 2. |
- Rath, Kristin M., et al.
(författare)
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Linking bacterial community composition to soil salinity along environmental gradients
- 2019
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Ingår i: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 13, s. 836-846
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Tidskriftsartikel (refereegranskat)abstract
- Salinization is recognized as a threat to soil fertility worldwide. A challenge in understanding the effects of salinity on soil microbial communities is the fact that it can be difficult to disentangle the effects of salinity from those of other variables that may co-vary with salinity. Here we use a trait-based approach to identify direct effects of salinity on soil bacterial communities across two salinity gradients. Through dose–response relationships between salinity and bacterial growth, we quantified distributions of the trait salt tolerance within the communities. Community salt tolerance was closely correlated with soil salinity, indicating a strong filtering effect of salinity on the bacterial communities. Accompanying the increases in salt tolerance were consistent shifts in bacterial community composition. We identified specific bacterial taxa that increased in relative abundances with community salt tolerance, which could be used as bioindicators for high community salt tolerance. A strong filtering effect was also observed for pH across the gradients, with pH tolerance of bacterial communities correlated to soil pH. We propose phenotypic trait distributions aggregated at the community level as a useful approach to study the role of environmental factors as filters of microbial community composition.
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| 3. |
- Rath, Kristin M., et al.
(författare)
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Linking Microbial Community Structure to Trait Distributions and Functions Using Salinity as an Environmental Filter
- 2019
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Ingår i: mBio. - 2161-2129. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- The structure and function of microbial communities vary along environmental gradients; however, interlinking the two has been challenging. In this study, salinity was used as an environmental filter to study how it could shape trait distributions, community structures, and the resulting functions of soil microbes. The environmental filter was applied by salinizing nonsaline soil (0 to 22 mg NaCl g-1). Our targeted community trait distribution (salt tolerance) was determined with dose-response relationships between bacterial growth and salinity. The bacterial community structure responses were resolved with Illumina 16S rRNA gene amplicon sequencing, and the microbial functions determined were respiration and bacterial and fungal growth. Salt exposure quickly resulted in filtered trait distributions, and stronger filters resulted in larger shifts. The filtered trait distributions correlated well with community composition differences, suggesting that trait distribution shifts were driven at least partly by species turnover. While salt exposure decreased respiration, microbial growth responses appeared to be characterized by competitive interactions. Fungal growth was highest when bacterial growth was inhibited by the highest salinity, and it was lowest when the bacterial growth rate peaked at intermediate salt levels. These findings corroborated a higher potential for fungal salt tolerance than bacterial salt tolerance for communities derived from a nonsaline soil. In conclusion, by using salt as an environmental filter, we could interlink the targeted trait distribution with both the community structure and resulting functions of soil microbes.IMPORTANCE Understanding the role of ecological communities in maintaining multiple ecosystem processes is a central challenge in ecology. Soil microbial communities perform vital ecosystem functions, such as the decomposition of organic matter to provide plant nutrition. However, despite the functional importance of soil microorganisms, attribution of ecosystem function to particular constituents of the microbial community has been impeded by a lack of information linking microbial processes to community composition and structure. Here, we apply a conceptual framework to determine how microbial communities influence ecosystem processes, by applying a "top-down" trait-based approach. By determining the dependence of microbial processes on environmental factors (e.g., the tolerance to salinity), we can define the aggregate response trait distribution of the community, which then can be linked to the community structure and the resulting function performed by the microbial community.
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| 4. |
- Rath, Kristin M., et al.
(författare)
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The impact of salinity on the microbial response to drying and rewetting in soil
- 2017
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 108, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- In saline soils, the severity of drought for the soil microbial community is exacerbated by accumulating concentrations of salts during drying. In this study we investigated how bacterial growth and respiration responses to drying-rewetting were affected by salinity. To do this, we adjusted a non-saline soil to four different salinities (0, 2, 7 and 22 mg NaCl g−1), followed by addition of plant material and a one-month incubation. Following the incubation period, we assessed the moisture dependence of respiration and growth, as well as the responses of bacterial growth and respiration to a cycle of air-drying followed by rewetting to optimal moisture. The inhibition of bacterial growth and respiration by reducing moisture increased with higher salt concentrations. As such, salinity was shown to increase the negative impact of drying on bacterial growth and alter the bacterial growth and respiration dynamics after rewetting. Drying-rewetting of soils with low salinity resulted in an immediate onset and gradual resuscitation of bacterial growth to levels similar to before drying. In contrast, in soils with higher salinity growth increased exponentially after a lag period of several hours. The duration of the lag period induced by salinity increased with the amount of salt added. The observed lag period matched previously reported results observed in response to more severe drying by e.g. longer duration of drought and drought combined with starvation. In treatments with a salt concentration ≤7 mg NaCl g−1 a high respiration pulse occurred immediately after rewetting and subsequently respiration declined. In the most saline treatment the initial respiration was reduced below the level of continuously moist soil to later increase exponentially in parallel with the increase in bacterial growth. We conclude that soil salinity increases the inhibition of microbial activity by low moisture, that fundamentally different responses to drying-rewetting cycles can be induced, and that high salt concentrations can substantially delay the pulse of respiration induced by rewetting dry soil.
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| 5. |
- Rath, Kristin M., et al.
(författare)
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The microbial community size, structure, and process rates along natural gradients of soil salinity
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 138
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Tidskriftsartikel (refereegranskat)abstract
- Over 840 M ha of arable land is affected by salinization, and the area is predicted to increase due to global change. Assessments of the status of the microbial community in saline soils have frequently been based on microbial biomass estimates, which might not accurately reflect microbial process rates in soil. Moreover, assessments of how the relative importance of major decomposer groups bacteria and fungi are affected by salinity remain inconclusive. In this study we set out to assess the soil microbial community size, structure and process rates along two salinity gradients. To distinguish between the direct effects of high salinity and indirect effects resulting from reduced soil organic matter (OM) concentrations in saline soils we also assessed the gradients following plant litter amendments to compensate for differences in OM content between soils and isolate the effect of salinity. The research aims were to (i) investigate the microbial biomass responses to salinity as estimated based on both PLFA concentrations and qPCR measurements and to compare these responses to those of respiration and microbial growth, (ii) compare the responses of bacteria and fungi to increased salinity and (iii) assess the responses of these microbial variables to the alleviation of OM scarcity expected in saline soils. Microbial biomass estimates generally were less negatively affected by salinity than bacterial growth and respiration, and were not correlated to rates of microbial growth or respiration rates. While bacterial growth was strongly inhibited by salinity, fungal growth was similar in soils of all salinities, indicating a higher fungal tolerance to salinity. OM additions increased process rates in saline soils and alleviated some of the negative impact of salinity on respiration and growth. In conclusion, this study demonstrates differential responses of saprotrophic fungi and bacteria to increasing salinity and that bacteria are directly impacted by soil salinity while fungi are responding to the indirect effect by salinity related to reduced plant C input.
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| 6. |
- Rath, Kristin, et al.
(författare)
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Salt effects on the soil microbial decomposer community and their role in organic carbon cycling: A review
- 2015
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 81, s. 108-123
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Forskningsöversikt (refereegranskat)abstract
- Salinization of soil is recognised as one of the most pressing environmental challenges to resolve for the next century. We here conduct a synoptic review of the available research on how salt affects decomposer microbial communities and carbon (C) cycling in soil. After summarizing known physiological responses of microorganisms to salinity, we provide a brief overview and qualification of a selection of widely applied methods to assess microorganisms in soil to date. The dominant approaches to characterise microbial responses to salt exposure have so far been microbial biomass and respiration measurements. We compile datasets from a selection of studies and find that (1) microbial biomass-carbon (C) per C held in soil organic matter shows no consistent pattern with long-term (field gradients) or short-term (laboratory additions) soil salinity level, and (2) respiration per soil organic C is substantially inhibited by higher salt concentrations in soil, and consistently so for both short-term and long-term salinity levels. Patterns that emerge from extra-cellular enzyme assessments are more difficult to generalize, and appear to vary with the enzyme studied, and its context. Growth based assessments of microbial responses to salinization are largely lacking. Relating the established responses of microbial respiration to that of growth could provide an estimate for how the microbial C-use efficiency would be affected by salt exposure. This would be a valuable predictor for changes in soil C sequestration. A few studies have investigated the connection between microbial tolerance to salt and the soil salinity levels, but so far results have not been conclusive. We predict that more systematic inquiries including comprehensive ranges of soil salinities will substantiate a connection between soil salinity and microbial tolerance to salt. This would confirm that salinity has a direct effect on the composition of microbial communities. While salt has been identified as one of the most powerful environmental factors to structure microbial communities in aquatic environments, no up-to-date sequence based assessments currently exist from soil. Filling this gap should be a research priority. Moreover, linking sequencing based assessments of microbial communities to their tolerance to salt would have the potential to yield biomarker sets of microbial sequences. This could provide predictive power for, e.g., the sensitivity of agricultural soils to salt exposure, and, as such, a useful tool for soil resource management. We conclude that salt exposure has a powerful influence on soil microbial communities and processes. In addition to being one of the most pressing agricultural problems to solve, this influence could also be used as an experimental probe to better understand how microorganisms control the biogeochemistry in soil. (C) 2014 Elsevier Ltd. All rights reserved.
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| 7. |
- Revill, James, et al.
(författare)
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Lessons learned from implementing education on dual-use in Austria, Italy, Pakistan and Sweden
- 2012
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Ingår i: Medicine, Conflict and Survival. - : Informa UK Limited. - 1362-3699 .- 1743-9396. ; 28:1, s. 31-44
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides insights into the achievements and challenges of implementing education on dual-use in four countries: Austria, Italy, Pakistan and Sweden. It draws attention to the different institutional mechanisms through which dual-use education may be introduced into academic curricula and some of the difficulties encountered in this process. It concludes that there is no ‘one size fits all’ approach to the implementation of dual-use education. Rather, initiatives must be tailored to suit the teaching traditions, geographical and historical context in which they are being delivered. However, a number of common principles and themes can be derived from all four cases. All these courses bring together a number of different topics that place ‘dual-use’ in the broader context of biosafety, biosecurity, ethics, law and the environment. The case studies suggest that success in this area depends largely on the leadership and commitment of individuals directly involved in teaching, who are active within the scientific community.
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