Browsing by Subject "Phytoremediation"

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Arbuscular mycorrhizal fungi-based bioremediation of mercury: insights from zinc and cadmium transporter studies
(2023) Guo, Yaqin; Martin, Konrad; Hrynkiewicz, Katarzyna; Rasche, Frank; Guo, Y.; Faculty of Agricultural Sciences, Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, 70593, Stuttgart, Germany; Martin, K.; Faculty of Agricultural Sciences, Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, 70593, Stuttgart, Germany; Hrynkiewicz, K.; Department of Microbiology, Faculty of Biological and Veterinary Sciences, Nicolaus Copernicus University, 87-100, Torun, Poland; Rasche, F.; Faculty of Agricultural Sciences, Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, 70593, Stuttgart, Germany
Phytoremediation, a sustainable approach for rehabilitating mercury (Hg)-contaminated soils, can be enhanced by arbuscular mycorrhizal (AM) fungi, which promote plant growth and metal uptake, including Hg, in contaminated soils. Hg, despite lacking a biological function in plants, can be absorbed and translocated using Zn and/or Cd transporters, as these elements belong to the same group in the periodic table (12/2B). In fact, the specific transporters of Hg in plant roots remain unknown. This study is therefore to provide fundamental insights into the prospect to remediate Hg-contaminated soils, with a focus on the role of AM fungi. The hypothesis posits that Hg uptake in plants may be facilitated by transporters responsible for Zn/Cd, affected by AM fungi. The Scopus database was used to collect studies between 2000 and 2022 with a focus on the ecological role of AM fungi in environments contaminated with Zn and Cd. Particular emphasis was laid on the molecular mechanisms involved in metal uptake and partitioning. The study revealed that AM fungi indeed regulated Zn and/or Cd transporters, influencing Zn and/or Cd uptake in plants. However, these effects vary significantly based on environmental factors, such as plant and AM fungi species and soil conditions (e.g., pH, phosphorus levels). Given the limited understanding of Hg remediation, insights gained from Zn and Cd transporter systems can guide future Hg research. In conclusion, this study underscores the importance of considering environmental factors and provides fundamental insights into the potential of Hg phytoremediation with the assistance of AM fungi.
Ecological and molecular characteristics of arbuscular mycorrhizal fungi (AMF) on mercury phytoremediation
(2023) Guo, Yaqin; Frank, Rasche
Environmental pollution caused by harmful chemicals represents a major challenge worldwide. Among these, heavy metals (HM) in soils are of particular concern due to their persistence, toxicity, and bioaccumulation which can significantly threaten human health, plant growth, and ecosystem integrity. Phytoremediation, which uses plants to extract pollutants from soils, has been recognized as a promising approach to remediate HM-contaminated soils. Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation has shown great potential to enhance plant growth and metal uptake by forming a mutual association between plant roots and AMF, which can improve nutrient uptake and tolerance to environmental stress. Despite its potential, however, the effectiveness of this approach can be limited by various factors, such as environmental and geographic factors, soil properties, and plant-microbe interactions. An advanced fundamental understanding of both ecological and molecular characteristics of this technology is thus crucial to improve its effectiveness and application potential. Therefore, the impetus of this doctoral thesis was to investigate the potential of AMF in phytoremediation of soils contaminated with HM, with a particular focus on mercury (Hg) remediation. The first study (Chapter 2) contributes to the ecological understanding of AMF in a degraded ecosystem. In this study, two geographically distinct, abandoned gold mining locations in Ghana were selected and the genetic diversity and composition of AMF communities both in the rhizosphere and roots of the pioneer plant Pueraria phaseoloides (Roxb.) Benth. (tropical kudzu) were analyzed using a metagenomic sequencing approach. To determine the primary factor shaping AMF communities, both biotic (plant identity) and abiotic factors (geographic locations and soil conditions) were examined. In total, 195 amplicon sequence variants (ASV) affiliated to eight genera of the phylum Glomeromycota were identified. The root compartment showed a lower diversity than the rhizosphere soils and a difference of AMF compositions between the two compartments was detected irrespective of geographical location. Moreover, co-occurrence network analysis revealed two different keystone species in the two compartments, i.e., Acaulospora in rhizosphere soil and Rhizophagus in roots. The high abundance of Rhizophagus in the roots of P. phaseoloides was the result of a good match of functions between plant and AMF. Collectively, the results indicated that plant compartment (root versus rhizosphere) is the main factor shaping AMF communities associated with P. phaseoloides. The second study (Chapter 3) comprises a research synthesis of the role of AMF in zinc (Zn), cadmium (Cd), and Hg bioremediation. The study assumed that mycorrhization plays a role in modulating the uptake of Hg, facilitated by Zn and/or Cd transporters. The synthesis demonstrated that AMF have the ability to regulate the transporters responsible for Zn and Cd uptake and transport, such as ZIP (zinc-iron permease or ZRT-IRT-like protein), CDF (cation diffusion facilitator), NRAMP (natural resistance-associated macrophage proteins), and HMA (heavy metal ATPase). This regulation can either enhance or inhibit the uptake and transport of Zn or Cd. The extent of this regulation is influenced by multiple factors, such as the plant species, the species of AMF involved, and soil conditions, including pH and elements such as phosphorus (P). It was concluded that future research is needed to investigate the optimal environmental conditions under which AMF are effective in Hg remediation for appropriate application. The third study (Chapter 4) offers essential insights into the distinct functions of AMF symbiosis in Hg partitioning in plants. This relationship was assessed in the context of Zn uptake mechanisms and the expression of two Zn transporter genes (ZIP2 and ZIP6). Zn is crucial for plants and has a similar outer electronic configuration as Hg, which implies a potential competition for the same transporters. In a greenhouse experiment, plants of Medicago truncatula were exposed to different Hg concentrations with and without inoculation of the AMF species Rhizophagus irregularis. This study demonstrated that mycorrhizal symbiosis improved plant Hg tolerance under Hg exposure, but the specific roles of mycorrhizal symbiosis in Hg partitioning depended on Hg concentrations in the substrate. A negative relationship between Hg and Zn concentrations in roots was observed, although the expression of Zn transporters (ZIP2 and ZIP6) by mycorrhizal inoculation was upregulated irrespective of Hg concentrations in the substrate. More importantly, mycorrhizal colonization reduced Hg concentrations in leaves compared to controls, regardless of Hg concentrations in the substrate. This study demonstrated that mycorrhizal symbiosis influences Hg uptake in M. truncatula and highlights the importance of AMF in phytoremediation. Overall, this doctoral thesis extends the understanding of AMF in phytoremediation with insights from both ecological and molecular perspectives and provides a knowledge basis to realize the potential and implementation of this technology.
Governance of land rehabilitation and remediation: case studies of Ghana’s small-scale mining sector
(2024) Adu-Baffour, Ferdinand Ababio; Birner, Regina
The artisanal and small-scale mining (ASM) sector is a complex and evolving industry that presents unique challenges within the global resource landscape. Despite its traditional labeling as artisanal, ASM operations are increasingly becoming mechanized, utilizing heavy machinery and hazardous chemicals such as mercury and cyanide for mineral extraction. Concurrently, the informal nature of most ASM operations limits effective top-down regulatory enforcements due to governance challenges. These developments have led to wide spreads of degraded, contaminated and abandoned rural community lands which also serve as valuable agricultural and forest lands for inhabitants of affected mining communities. While the existing literature has extensively analyzed the impacts of these developments on local, national, and global economies, ecologies, health, and welfare, there remains a notable gap in understanding the governance of rehabilitating and remediating affected environments post-mineral extraction. Furthermore, phytoremediation – a biological innovation which can help remediate contaminated sites and address the problem of soil degradation and erosion, with reported economic and environmental benefits – has only seen very limited global commercial adoption. In regions where traditional remediation approaches are financially untenable, like in the Global South, however, phytoremediation is argued to be a suitable and viable solution towards a greener future for remediation and environmental restoration. This thesis aims to address the knowledge gaps pertaining to the governance of rehabilitating and remediating affected environments affected by mineral extraction in the artisanal and small-scale mining (ASM) sector. Specifically, it focuses on systematically investigating the governance challenges in ASM, exploring community-based solutions for sustainable land restoration, and proposing a framework for the broader-based application of phytoremediation to address land contamination in the small-scale gold mining sector in Ghana. These research objectives are structured around three chapters, with the first two focusing on empirical case studies and the last chapter serving as a review of scientific and grey literature, as well as project reports on land rehabilitation and phytoremediation. Chapter 2, which addresses the first objective, delves into the obstacles hindering the implementation of the legal framework for artisanal small-scale mining (ASM) in Ghana. The first part conducts an institutional analysis of the legal and political framework governing Ghana’s small scale mining sector, with a particular focus on its implications for post-mined land rehabilitation efforts. This is followed by an assessment of the practical application of the legal framework in the context of small-scale gold mining (ASGM) value chain, using the Process Net-Mapping tool along with stakeholder interviews. The study reveals outdated legislation, formal licensing bureaucracies, land tenure issues, and ineffective collaboration among stakeholders as major bottlenecks. Drawing on these insights, the chapter discusses the broader implications of the findings for the effective running of the ASGM value chain and recommends, among other things, the adoption of collaborative governance systems, like co-management, to ensure sustainability. Chapter 3, which addresses the second objective, examines community-based solutions for sustainable mined land restoration through a case study of an NGO-initiated project in five active mining communities in Ghana's Amansie West district. The chapter utilizes a combination of qualitative methods including the participatory Net-Mapping tool to explore conditions under which local communities would engage in restoration efforts without financial incentives, revealing community support, using communal labor, dependent on factors like land tenure arrangements and local leadership influence. The study underscores the potential of community-led efforts for land rehabilitation, emphasizing the role of social networks, norms, and land tenure structures. Chapter 4, which addresses the third objective, introduces a conceptual framework for the effective and sustainable application of phytoremediation to clean contaminated lands resulting from mining activities. This is the result of insights drawn from existing phytoremediation literature, including case studies where the field application or/and commercialization of phytoremediation has been successful, and lessons gleaned from other real-world applications of the technology. The framework encompasses technical considerations across the phytoremediation process and identifies the socio-cultural, economic, political, and institutional conditions necessary for successful large-scale implementation. The paper provides valuable guidance for regions seeking to leverage phytoremediation to benefit society and the environment. In conclusion, this thesis contributes to understanding the challenges facing the ASM sector and proposes innovative solutions to address governance issues, promote community-based land restoration, and facilitate the scaling of phytoremediation initiatives for sustainable development in the mining sector, particularly in developing regions. The holistic approach advocated in this thesis underscores the importance of legal reforms tailored to the constantly evolving ASM sector, stakeholder collaboration, adaptive governance systems, and community engagement to effectively navigate the intricate ASM landscape and maximize its beneficial effects on local livelihoods and development worldwide.