| 1. |
- Bölscher, Tobias
(författare)
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Adaptation Turning Points in River Restoration? The Rhine Salmon Case
- 2013
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Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 5, s. 2288-2304
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Tidskriftsartikel (refereegranskat)abstract
- Bringing a sustainable population of Atlantic salmon (Salmo salar) back into the Rhine, after the species became extinct in the 1950s, is an important environmental ambition with efforts made both by governments and civil society. Our analysis finds a significant risk of failure of salmon reintroduction because of projected increases in water temperatures in a changing climate. This suggests a need to rethink the current salmon reintroduction ambitions or to start developing adaptive action. The paper shows that the moment at which salmon reintroduction may fail due to climate change can only be approximated because of inherent uncertainties in the interaction between salmon and its environment. The added value of the assessment presented in this paper is that it provides researchers with a set of questions that are useful from a policy perspective (by focusing on the feasibility of a concrete policy ambition under climate change). Thus, it offers opportunities to supply policy makers with practical insight in the relevance of climate change.
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| 2. |
- Bölscher, Tobias, et al.
(författare)
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Changes in pore networks and readily dispersible soil following structure liming of clay soils
- 2021
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 390
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Tidskriftsartikel (refereegranskat)abstract
- Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (ø ≥ 0.3 mm) in soil columns and mesopores (ø ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (ε>1.0 mm) and medium sized macropores (ε0.3–1.0 mm) towards smaller macropores (ε0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space.
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| 3. |
- Bölscher, Tobias
(författare)
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Decomposition of soil organic matter under a changing climate : a matter of efficiency?
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soil organic matter is the largest carbon (C) pool in the terrestrial C cycle, and soil CO₂ emissions surpass anthropogenic emissions from fossil fuel combustion by a factor of nine. Therefore, mechanisms controlling C stabilisation in soils and its feedback to climate change are widely debated. During decomposition, microbial substrate-use efficiency is an important property because it determines the allocation of substrate C to biosynthesis and respiratory losses. High efficiency values indicate that C primarily remains in soils while low efficiency implies that C is primarily lost into the atmosphere. Despite empirical evidence that efficiency is temperature sensitive, traditional Earth system models treat this property as a constant. The aim of this thesis was to improve our mechanistic understanding of drivers regulating substrate-use efficiency with special consideration to climate change. It investigated the impacts of (i) temperature, (ii) microbial community composition and (iii) substrate quality on substrate-use efficiency. Within the thesis, a microbial energetics approach was applied and further developed using isothermal calorimetry. Further, the thesis compared common approaches for measuring microbial substrate-use efficiency, and the implications of the resultant empirical data for projected C stocks were tested using a modelling approach. Substrate-use efficiency was generally temperature sensitive and decreased with increasing temperature. The observed temperature responses were non-linear and varied across land use management systems. The changes in substrate-use efficiency with temperature were driven rather by changes in microbial physiology than by shifts in active microbial communities. Nevertheless, fungi and Gram-negative bacteria tended towards relatively higher efficiencies. Efficiencies varied among utilised substrates, but substrate quality per se was a poor proxy for efficiency. Projected losses from soil C stocks varied across land use management systems and were up to 39 % and 15 % for grassland and forest systems, respectively. Results from the modelling approach confirmed that substrate-use efficiency is one of the factors to which soil C stocks react most sensitively. Findings from this thesis emphasise the importance of furthering our understanding of substrate-use efficiency for reliable climate projections.
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| 4. |
- Bölscher, Tobias, et al.
(författare)
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Differences in substrate use efficiency : impacts of microbial community composition, land use management, and substrate complexity
- 2016
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 52:4, s. 547-559
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Tidskriftsartikel (refereegranskat)abstract
- Microbial substrate use efficiency is an important property in process-based soil organic matter models, but is often assumed to be constant in mechanistic models. However, previous studies question if a constant efficiency is appropriate, in particular when evaluating carbon (C) cycling across temperatures and various substrates. In the present study, we evaluated the relation between substrate use efficiency, microbial community composition and substrate complexity in contrasting long-term management regimes (47–49 years of either arable, ley farming, grassland, or forest systems). Microbial community composition was assessed by phospholipid fatty acid analysis and three indices of substrate use efficiencies were considered: (i) thermodynamic efficiency, (ii) calorespirometric ratio, and (iii) metabolic quotient. Three substrates, d-glucose, l-alanine, or glycogen, varying in complexity, were added separately to soils, and heat production as well as C mineralization was determined over a 32-h incubation period at 12.5 °C. Microbial communities from forest systems were most efficient in utilizing substrates, supporting our hypothesis that maturing ecosystems become more efficient. These changes in efficiency were linked to microbial community composition with fungi and Gram-negative bacteria being important biomarkers. Despite our initial hypothesis, complex substrate such as glycogen was utilized most efficiently. Our findings emphasize that differences in land use management systems as well as the composition of soil organic matter need to be considered when modelling C dynamics in soils. Further research is required to establish and evaluate appropriate proxies for substrate use efficiencies in various ecosystems.
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| 5. |
- Bölscher, Tobias, et al.
(författare)
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Land-use alters the temperature response of microbial carbon-use efficiency in soils - a consumption-based approach
- 2020
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 140
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Tidskriftsartikel (refereegranskat)abstract
- Soil organic carbon (SOC) is a substantial source of atmospheric CO2, but also a large cause of uncertainties in Earth-system models. A principal control on soil CO2 release is the carbon-use efficiency (CUE) of microbial communities, which partitions the carbon (C) allocation between biosynthetic stabilization and CO2 respiration during SOC decomposition. In Earth-system models, CUE is commonly considered as a constant, although it should be susceptible to environmental factors such as temperature. We explored CUE across a set of land-uses and temperatures, and we show the hitherto neglected phenomenon that land-use can alter the temperature response of CUE. In arable soils, CUE was constant over a temperature range between 5 and 20 degrees C, but it decreased with temperature in ley farming, grassland, and forest soils at temperatures above 12.5 degrees C. The decrease in CUE was strongest for forest soils. Implementing our findings into a soil-C model revealed substantial differences in projected SOC losses: Assuming an increase of mean annual temperature of 2 or 4 degrees C, soils were projected to lose up to 6 or 15% of their current SOC, respectively, until they reach a new steady-state. These projections varied among land-uses. Our findings confront the current representation of CUE in global C models and challenges C sequestration strategies based on land-use changes, because land-uses such as e.g. forest ecosystems with current high C storage may lose substantially more C than agricultural soils due to strong declines of CUE.
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| 6. |
- Bölscher, Tobias, et al.
(författare)
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Temperature sensitivity of substrate-use efficiency can result from altered microbial physiology without change to community composition
- 2017
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 109, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- Mechanisms controlling carbon stabilisation in soil and its feedback to climate change are of considerable importance. Microbial substrate-use ef organic matter. It determines the allocation of substrate towards biosynthetic stabilisation of carbon and for respiratory losses into the atmosphere. Previously, it was observed that substrate-use ef declines with an increase in temperature and that it varies across organic substrates. Yet, our mechanistic understanding of processes causing the temperature sensitivity of substrate-use ef Changes in substrate-use ef communities, (ii) changes in microbial physiology within the same community, or (iii) a combination of both. In the present study, we evaluated the link between microbial community composition and substrate-use ef We found only minor shifts in microbial community composition, despite large differences in substrateuse ef changes in substrate-use ef emphasize that future studies should focus on resolving long-term trade-offs between physiological and community inficiency is an important property during decomposition of soilficiencyficiency is limited.ficiency could be triggered by (i) shifts in the active components of microbialficiency, combining measurements of carbon mineralisation and microbial energetics.ficiencies across incubation temperatures and substrate additions. We conclude that short-termficiency were mainly caused by changes in microbial physiology, butfluences on substrate-use efficiency.
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| 7. |
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| 8. |
- Bölscher, Tobias
(författare)
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Turning points in climate change adaptation
- 2015
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Ingår i: Ecology and Society. - 1708-3087. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- Concerned decision makers increasingly pose questions as to whether current management practices are able to cope with climate change and increased climate variability. This signifies a shift in the framing of climate change from asking what its potential impacts are to asking whether it induces policy failure and unacceptable change. In this paper, we explore the background, feasibility, and consequences of this new framing. We focus on the specific situation in which a social-political threshold of concern is likely to be exceeded as a result of climate change, requiring consideration of alternative strategies. Action is imperative when such a situation is conceivable, and at this point climate change becomes particularly relevant to decision makers. We call this situation an "adaptation turning point." The assessment of adaptation turning points converts uncertainty surrounding the extent of a climate impact into a time range over which it is likely that specific thresholds will be exceeded. This can then be used to take adaptive action. Despite the difficulty in identifying adaptation turning points and the relative newness of the approach, experience so far suggests that the assessment generates a meaningful dialogue between stakeholders and scientists. Discussion revolves around the amount of change that is acceptable; how likely it is that unacceptable, or more favorable, conditions will be reached; and the adaptation pathways that need to be considered under these circumstances. Defining and renegotiating policy objectives under climate change are important topics in the governance of adaptation.
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| 9. |
- Herrmann, Anke, et al.
(författare)
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Simultaneous screening of microbial energetics and CO2 respiration in soil samples from different ecosystems
- 2015
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 83, s. 88-92
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Tidskriftsartikel (refereegranskat)abstract
- The calorespirometric ratio, i.e. the ratio of heat production-to-CO2 production has been used to evaluate metabolism and microbial carbon use efficiency in soil systems. But limited sample throughput and high variability when evaluating microbial energetics and CO2 respiration separately hampered its applicability in soil science. In this study we tested if heat flows and CO2 respiration can be determined simultaneously in the same soil sample without any measurable experimental biases. Heat outputs were not significantly different when CO2 respiration was determined concurrently by means of a colorimetric method. Our method provides a simple, cheap and rapid screening of the calorespirometric ratio, and in comparison with previous studies, the reproducibility of the ratios was improved. Its non-destructive nature allows combination with the characterization of the chemical and biological composition in soil systems. Used together these methods have the potential to improve our understanding of microbial communities, their processes and activities below-ground. (C) 2015 Elsevier Ltd. All rights reserved.
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| 10. |
- Le Noë, Julia, et al.
(författare)
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Soil organic carbon models need independent time-series validation for reliable prediction
- 2023
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Ingår i: Communications Earth & Environment. - 2662-4435. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- Numerical models are crucial to understand and/or predict past and future soil organic carbon dynamics. For those models aiming at prediction, validation is a critical step to gain confidence in projections. With a comprehensive review of ~250 models, we assess how models are validated depending on their objectives and features, discuss how validation of predictive models can be improved. We find a critical lack of independent validation using observed time series. Conducting such validations should be a priority to improve the model reliability. Approximately 60% of the models we analysed are not designed for predictions, but rather for conceptual understanding of soil processes. These models provide important insights by identifying key processes and alternative formalisms that can be relevant for predictive models. We argue that combining independent validation based on observed time series and improved information flow between predictive and conceptual models will increase reliability in predictions.
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