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- Guasconi, Daniela, 1992-
(författare)
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The hidden half of the meadow : Interactions between drought, soil carbon, roots and soil microbial communities
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soil is a hidden ecosystem which harbours plant roots and countless microorganisms, vital for sustaining life aboveground. These belowground communities provide essential ecosystem services like soil stabilisation and organic matter decomposition. Soil is also one of the largest terrestrial carbon repositories, and land management strategies aimed at increasing organic matter inputs from plants, such as compost additions, can promote further soil carbon accumulation. Because organic carbon is important for soil water retention, this management may also help to increase resilience against more frequent and intense droughts. Although roots and microbial communities are largely acknowledged to play a key role in regulating the carbon cycle, there are still many open questions regarding the link between above- and belowground processes and ecosystem functions. Observing climate- and management-driven changes in the soil habitat is fundamental for understanding how ecosystems respond to environmental change.The aim of this thesis is to explore the relationship between soil properties, plant communities, and soil microbial communities in response to environmental changes. The research builds on a meta-analysis of drought effects on grasslands, and a multifactorial field experiment which combined three years of precipitation reduction and a compost treatment in two Swedish grasslands. We analysed the response of roots and soil microbial communities to drought and compost amendments, and identified environmental factors behind their large spatial variability. Finally, we tested the effects of compost additions on soil carbon storage and its interactions with drought.The results of the meta-analysis indicate that, on a global scale, grassland roots and shoots have diverging responses to drought duration and intensity, with long-term climate mediating that difference. At the local scale assessed in the field experiment, we observed that the spatial patterns of soil microbial communities were driven by soil properties and vegetation. Growing season drought affected roots only at trait level, but did not significantly affect microbial communities. Positive effects of compost on aboveground plant productivity and fungal growth were detectable after three years. Compost amendments also increased the percentage of total soil carbon, but no net increase in soil carbon stocks was detected. Spatial variability in roots and microbial communities was larger than the treatment effects, and was important in shaping microbial community composition and determining grassland responses to drought.Taken together, these findings suggest that roots and microbial communities are likely to be tolerant to drought a within the timescale of this experiment, but we did not observe an increase soil carbon sequestration or drought resilience when adding compost. This thesis highlights the importance of considering soil processes as complementary to aboveground observations when studying carbon dynamics, predicting ecosystem responses to environmental change, and developing sustainable land management practices.
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| 2. |
- Livsey, John, 1983-
(författare)
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Sustainable agriculture : From global challenges to local land management
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite the success of agriculture management practices in increasing the availability of food needed to meet the requirements of the expanding global population, there are increasing demands placed on the resources on which the sector depends. Opportunities for the development of agricultural systems are constrained by increasing competition, from other sectors, for shared resources. In tackling this constraint, agricultural management solutions are often narrowly focused on problems related to single resources. But this single focus may lead to unintended trade-offs. To make sound management decisions, there is a need to better understand trade-offs which may occur from resource use efficiency solutions implemented in the agricultural sector. With a particular focus on soil and water resources, the aim of this thesis was to investigate trade-offs that occur, when meeting demands placed on agriculture systems, if management solutions are narrowly focused. Broadly, we hypothesize that approaches to land management that take a more holistic view of agricultural systems being part of an ecosystem mosaic should be adopted to ensure sustainability. A global assessment of potential land requirements shows that national level production of sufficiently nutritious food may be constrained by land availability, such that allocation of land to nutritious crop production might come at the cost of lost land for other crops or uses. This constraint will be the most prevalent in African states. In further studies, we focused on the management of water resources, which are becoming particularly limiting for crops that have high water demands, such as rice. Through a meta-analysis of paired plot experiments, which assessed the effect of water saving irrigation in rice production, and soil sampling within An Giang, a major rice producing province of Vietnam, we examined the effect of water management practices on soil properties. The meta-analysis finds that significant reductions in soil organic carbon, and potentially organic matter bound nutrients, have been observed when water efficient practices replace continual flood irrigation. This suggests that, although yield reductions may not be seen in the short term, water saving irrigation may, over time, lead to reductions in soil fertility and yields. Within An Giang province, there are concerns regarding the loss of flood-borne, nutrient rich, sediments in fields where the annual flood waters have been completely regulated. However, we find that this complete regulation does not result in reduced soil nutrient properties when compared to areas where floods are only partially regulated. The effect of different land management practices on soil properties were further explored within the Kilombero Valley, Tanzania. Comparing farming practices along a gradient of intensity, we found contrasting effects of irrigation and fertilization, with irrigation increasing soil organic carbon and fertilization reducing soil organic carbon. Overall, the results of this thesis highlight the importance of looking beyond meeting short term needs, which can have negative long term consequences. The success of land management practices implemented now do not, necessarily, equate to their continued success in the future. As demands placed on agriculture are going to increase, the long term trade-offs which may occur from present practices must be at the forefront of agricultural management.
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| 3. |
- Maneas, Georgios, 1980-
(författare)
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Towards co-management of Gialova Lagoon : A Natura 2000 coastal wetland in Messinia, Greece
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The management of Natura 2000 sites is considered as the cornerstone for the conservation and restoration of biodiversity within Europe. However, protected ecosystems provide a plethora of benefits to local societies, and support the local economy. Thus, to seek solutions for complex environmental issues within Natura 2000 sties it is imperative to approach the site of concern as a connected social-ecological system, and to strengthen the participation of stakeholders in decision-making following a co-management approach.Gialova Lagoon wetland, in Messinia, Greece represents an example of Natura 2000 site which needs to be managed. The overall aim of the PhD thesis was to assess the problem of lagoon salinization, and provide policy recommendations for wetland restoration and management of associated freshwater resources under a changing climate. The thesis has followed a social-ecological approach, by integrating DPSIR framework with participatory Systems Dynamic modelling and the concept of ecosystem services. Knowledge gaps about major social and ecological components were assessed by applying a variety of methods, namely (a) field monitoring and observations, (b) GIS analyses, (c) consultation with stakeholders, (d) modelling and scenarios.The thesis results suggested that past human interventions had multi-fold effects on the Gialova Lagoon wetland, namely hydrology alteration, ecosystem fragmentation, loss and transformation of natural habitats. Furthermore, the combined effects of alterations in hydrology and climate change have led to increased salinity in the wetland over time. These alterations had profound implications on wetland ecosystem services such as the diversity of habitats and waterbirds and the provision of fish. Under contemporary hydrological connectivity and on-going climatic conditions, the mean annual salinity of the lagoon has increased from approximately 35 g/L during the period 2016-2018 to approximately 40 g/L during the period 2021-2023 indicating a salinization increase of approximately 1 g/L per year. To identify restoration alternatives, the work under the PhD thesis has engaged scientists with local stakeholders from the sectors of agriculture, fishing, tourism, and public administration, in a co-management approach. The end product, an SDM (Systems-Dynamics model) co-created with stakeholders, was suitable for exploring scenarios for salinity regulation and management of associated freshwater resources, under a changing climate (RCP 4.5). The derived management suggestions, namely restoration of the connectivity with the surrounding freshwater bodies (river, artesian springs) and between habitats (e.g., lagoon-marshes), could result in the de-salinization of the lagoon within a 10-year period, and could be applied within the Natura 2000 framework as they consider social and ecological needs (e.g. enhancement of biodiversity and fish production). However, under current abstraction rates for irrigation and municipal water-supply, there is a high risk of groundwater scarcity during years with dry conditions, and thus investments in water-saving technologies (e.g. smart irrigation) should be promoted to ensure adequate water availability for restoration, and enhanced resilience of the local economy against groundwater scarcity.
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| 4. |
- Chakrawal, Arjun, 1992-
(författare)
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Novel approaches in modeling of soil carbon : Upscaling theories and energetics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soils contain more carbon (C) than terrestrial (above ground) and atmospheric carbon combined. Mismanagement of soil C could lead to increased greenhouse gas emissions, whereas practices leading to increased C storage would help mitigate climate change while improving soil fertility and ecological functions. At the center of these complex feedbacks, soil microorganisms play a pivotal role in the cycling of C and nutrients, and thus in soil-climate interactions. However, this role is not fully understood; therefore, developing new methods for studying their dynamics is essential for an understanding of bio-physicochemical processes leading to mineralization or stabilization of soil organic matter (SOM).Current soil C cycling models lack a robust upscaling approach that links SOM decomposition from process (μm) to observation scale (cm to km). Moreover, these models often neglect energy fluxes from microbial metabolism, which may provide additional constraints in model parameterization and alternative observable quantities such as heat dissipation rate to study decomposition processes. In this doctoral work, I investigated two aspects of microbial processes and their consequences for SOM dynamics: 1) use of energetics to constrain SOM dynamics by explicitly accounting for thermodynamics of microbial growth, and 2) spatial constraints at microscale resulting from the non-uniform distribution of microorganisms and substrates.In the first part of the thesis, I developed a general mass and energy balance framework for the uptake of added substrates and native SOM. This framework provided the theoretical underpinnings for understanding variations in the calorespirometric ratios—the ratio of rates of heat dissipation to CO2 production—a useful metric used as a proxy for microbial carbon-use efficiency (CUE). Moreover, in a follow-up work, I extended this mass-energy framework to describe dynamic (time-varying) conditions, which was used to interpret rates of heat and CO2 evolution from different soils amended with glucose. The dynamic mass-energy framework was also used as a tool for data-model integration and estimation of microbial functional traits, such as their CUE and maximum substrate uptake rates. In the second part of the thesis, I linked the micro and macroscale dynamics of decomposition using scale transition theory. The findings of this study were further validated from laboratory experiments, in which spatial heterogeneity in the added substrate was manipulated.Results from the first part show that the calorespirometric ratios can be used to identify active metabolic pathways and to estimate CUE. Further, the heat dissipation rate can be used as a reliable complement or alternative to mass fluxes such as respiration rates for estimating microbial traits and constraining model parameters. In the second part, I show that the co-location of microorganisms and substrates increased, and separation decreased the microbial activity measured as heat dissipation from the incubation experiment. These results were in line with the expectation from the scale transition theory. In summary, this work provides novel approaches for studying soil C cycling and explicitly highlights a way forward to address two fundamental issues in microbial decomposition—the role of spatial heterogeneities and of energetic constraints on microbial metabolisms.
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