Principles of classification of medicinal plants as hyperaccumulators or excluders

Strategies of plants, known as metallophytes, in response to metal excess are explored. Specific features of medicinal plants related to metal exposition are discussed. Different parameters used for metallophyte classification are discussed. Bioaccumulation and translocation factors are characterized. Chamomile (Matricaria recutita L.), one of the most important medicinal plants, is presented as a case history. Based on actual knowledge of plant response to metal excess and published data related to chamomile, it has been concluded that this plant species is Cd hyper/accumulator. Thus, chamomile can manifest high potential for cleaning-up (phytoremediation) of the soils contaminated with cadmium. However, it should be stressed that cultivation of this medicinal plant under natural conditions for pharmaceutical use should be carefully supervised.     

Fitness and genetic variation of Viola calaminaria, an endemic metallophyte: implications of population structure and history

We investigated variations in genetic diversity and plant fitness in a rare endemic metallophyte of calamine soils, Viola calaminaria, in relation to population size, population connectivity and population history in order to evaluate and discuss potential conservation strategies for the species. Mean population genetic diversity (H(s) = 0.25) of V. calaminaria was similar to endemic non-metallophyte taxa. Twenty-one per cent of the genetic variation was partitioned among populations and a low (9%) but significant differentiation was found among geographical regions. Our results did not support the hypothesis that the acquisition of metal tolerance may result in reduced genetic diversity, and suggested that strict metallophytes do not exhibit higher inter-population differentiation resulting from scattered habitats. There were no relationships between population genetic diversity and population size. Significant correlations were found between plant fitness and (i) population size and (ii) connectivity index. Recently-founded populations exhibited the same level of genetic diversity as ancient populations and also possessed higher plant fitness. There was no indication of strong founder effects in recently-established populations. The results suggest that the creation of habitats through human activities could provide new opportunities for conservation of this species.     

Suitability of aromatic plants for phytoremediation of heavy metal contaminated areas: a review

Abstract

This review briefly elucidates the research undertaken and benefits of using aromatic plants for remediation of heavy metal polluted sites. A sustainable approach to mitigate heavy metal contamination of environment is need of the hour. Phytoremediation has emerged to be one of the most preferable choices for combating the metal pollution problem. Aromatic plants can be used for remediation of contaminated sites as they are non-food crops thus minimizing the risk of food chain contamination. Most promising aromatic plants for phytoremediation of heavy metal contaminated sites have been identified from families – Poaceae, Lamiaceae, Asteraceae, and Geraniaceae. They act as potential phytostabilisers, hyper accumulators, bio-monitors, and facultative metallophytes. Being high value economic crops, monetary benefits can be obtained by growing them in tainted areas instead of food crops. It has been observed that heavy metal stress enhances the essential oil percentage of certain aromatic crops. Research conducted on some major aromatic plants in this context has been highlighted in the present review which suggests that aromatic plants hold a great potential for phytoremediation. It has been reported that essential oil from aromatic crops is not contaminated by heavy metals significantly. Thus, aromatic plants are emerging as an ideal candidate for phytoremediation.

Highlights

? Aromatic plants hold a great potential for phytoremediation of heavy metal contaminated sites.

? Being high value economic crops, monetary benefits can be obtained by growing them in contaminated areas instead of food crops.

? Research done on some major aromatic plants in this context has been highlighted in the present review.     

Mine tailing disposal sites: contamination problems,remedial options and phytocaps for sustainable remediation

Mining practices and the absence of proper mine land reclamation has led to heavy metal contaminated sites with serious impact on the ecosystems and risk for human health. The origin of the contamination is often associated to mine tailing deposits because they are a source of the acid mine drainage (AMD). These areas are devoid of vegetation due to the harsh soil conditions that prevent the rooting of plant species. The remediation of these areas followed by revegetation is necessary to suppress the generation of the AMD and its negative effects on the ecosystems. Conventional remediation technologies for heavy metal contaminated sites are usually not applicable because of the high cost associated with chemicals and energy requirements, as well as the long treatment time to remediate large areas. In this study, the use of phytocapping for the remediation of mine tailing deposits and abandoned mine areas is reviewed. Phytocapping is cost effective, environmentally friendly and has multifunctional role against various problems of mine tailings: it provides erosion control, landscape rehabilitation, enhances the soil properties for further colonization of other more demanding vegetal species, reduces the leachability of metals downwards the groundwater, and favors the immobilization of metals forming less bioavailable species. The most critical step in phytocapping is the developing of the first vegetative cover because of the biotoxicity of the mine soil and mine tailings. Several amendment materials can be used to ameliorate soil conditions creating a favorable environment for the rooting of plants, as well as serving as a source of nutrients. Local plant species with fast growing are preferable because their adaptation to the soil and climate conditions favors their self-propagation.     

Facilitation Drives the Positive Effects of Plant Richness on Trace Metal Removal in a Biodiversity Experiment

Background

Phytoextraction is an environmentally acceptable and inexpensive technique for mine tailing rehabilitation that uses metallophyte plants. These plants reduce the soil trace metal contents to environmentally acceptable levels by accumulating trace metals. Recently, whether more trace metals can be removed by species-rich communities of these plants received great attention, as species richness has been reported having positive effects on ecosystem functions. However, how the species richness affects trace metals removal of plant communities of mine tailing is rarely known.

Methodology/Principal Findings

We examined the effects of species richness on soil trace metal removal in both natural and experimental plant communities. The root lengths and stem heights of each plant species were measured in order to calculate the functional diversity indices. Our results showed that trace metal (Cu, Cd, Pb and Zn) concentrations in mine tailing soil declined as species richness increased in both the natural and experimental plant communities. Species richness, rather than functional diversity, positively affected the mineralomass of the experimental plant communities. The intensity of plant-plant facilitation increased with the species richness of experimental communities. Due to the incremental role of plant-plant facilitation, most of the species had higher biomasses, higher trace metal concentrations in their plant tissues and lower malondialdehyde concentrations in their leaves. Consequently, the positive effects of species richness on mineralomass were mostly attributable to facilitation among plants.

Conclusions/Significance

Our results provide clear evidence that, due to plant-plant facilitation, species richness positively affects the removal of trace metals from mine tailing soil through phytoextraction and provides further information on diversity conservation and environmental remediation in a mine tailing environment.     

Site-specific risk assessment and integrated management decision-making: A case study of a typical heavy metal contaminated site,Middle China

A typical contaminated land was spatially investigated and assessed based on Chinese guidelines to establish remediation strategy for exploring the shortcomings of the current guidelines to suggest improvements. Results showed that Cr, As, Pb, and Cd should be regarded as the priority pollutants under sensitive land use, while Cr and As should be regarded as the priority pollutants under insensitive land use. Ingestion of soil for each studied metal appeared to be the main exposure pathway under both the land uses. The calculated screening values of the priority metals were conservative to certain extent—even some were lower than their background values. Therefore, an integrated risk management strategy was suggested and the hierarchic clean-up values were proposed considering the health risk, local background value, land remediation cases, current remediation technology, and financial cost. Consequently, it was suggested the clean-up values of Cr(VI), Cr, As, Pb, and Cd, under future sensitive land use, should be 7.5, 1000, 30, 250, and 1.4 mg/kg in the first class control layer, respectively. For future insensitive land use, the clean-up values of Cr(VI), Cr, As, Pb, and Cd should be 20.4, 8000, 60, 580, and 4.3 mg/kg in the first class control layer, respectively.     

金属型植物的研究进展

金属型植物是治理和修复土壤重金属污染的理想材料.综述了金属型植物的耐性机理、生殖生物学及进化生态学方面的研究进展,并对目前研究中存在的问题进行了分析和展望.     

Investigating the Vegetation–Soil Relationships on the Copper–Cobalt Rock Outcrops of Katanga (D. R. Congo), an Essential Step in a Biodiversity Conservation Plan

Plant communities of soils naturally enriched in copper and cobalt in Katanga (D. R. Congo) are critically threatened in the short term due to mining activities. For biodiversity conservation and ecosystem restoration purposes, there is an urgent need to acquire more knowledge on those plant communities including their diversity and their relationships to environmental factors. The classification of 62 vegetation plots located in 6 metal‐rich rocky hills in the Tenke Fungurume mining area resulted in 3 well‐defined steppic and steppic savanna communities. Canonical analysis showed that the community comprising the largest proportion of strictly endemic metallophytes (i.e. species that only occur on metal‐rich soils) developed in the soils with the most elevated concentrations of Cu and Co. However, contrasting species assemblages in the two other plant communities were explained by soil nutrients and percentage rocks in addition to heavy metal concentrations. The results of this study will assist with restoration efforts because they (1) provide a rigorous assessment of communities before a disturbance and (2) define essential edaphic conditions needed for the reestablishment of critical communities.     

Utilization of Multi-Tasking Non-Edible Plants for Phytoremediation and Bioenergy Source-A Review

Heavy metal contamination of land and freshwater resources is a serious concern worldwide. It adversely affects the health of animals, plants and humans. Therefore, remediation of toxic heavy metals must be highly considered. Unlike other techniques, phytoremediation is a holistic technology and can be used in large scale for soil remediation as it is costless, novel, environmentally-safe and solar-driven technology. Utilization of non-edible plants in phytoremediation is an ingenious technique as they are used to generate new bioenergy resources along with the remediation of contaminated soils. Some nonfood bioenergy crops such as Salix species, Miscanthus species, Populus species, Eucalyptus species, and Ricinus communis exhibit high capability to accumulate various metals and to grow in contaminated lands. However, there are still sustainable challenges facing coupling phytoremediation with bioenergy production from polluted lands. Therefore, there has long been a need for developing different strategies to resolve such challenges. In this article review, we will discuss the phytoremediation mechanism, the technique of phytoremediation coupling with bioenergy production, sustainable problems facing linking phytoremediation with energy production as well as possible strategies to enhance the efficiency of bioenergy plants for soil decontamination by improving their characteristics such as metal uptake, transport, accumulation, and tolerance.     

Edaphic niches of metallophytes from southeastern Democratic Republic of Congo: Implications for post-mining restoration

In southeastern D. R. Congo, about 550 metallophytes grow on soils with high copper and cobalt concentrations, 57 of which are endemics to these metalliferous environments. About 70% of those endemics are considered threatened by destruction of habitats through mining activities. To provide guidelines for future restoration programs, the edaphic ecological niches of eight endemic metallophytes (i.e. copper endemics) were studied using a pragmatic sampling method adapted for urgent conservation needs. Niches were modelled using violin plot along Cu, Co and C:N gradients representing the two main independent edaphic gradients among nine edaphic variables (C, N, C:N, K, P, pH, Co, Cu, and Mn). Copper endemics presented distinct edaphic niches along the copper and cobalt gradients, but differentiation was lower along the C:N gradient. In addition, edaphic elements presented covariations among them and metalliferous soils had higher nutrient and element content compared to the non-metalliferous soils of the region dominated by the Miombo woodland. The complexity of the soil composition and the edaphic niches of copper endemics revealed an important challenge in the implementation of the species conservation and the habitat restoration strategies of post-mining sites.     

Critical evaluation of municipal solid waste composting and potential compost markets

Mechanical biological treatment (MBT) of mixed waste streams is becoming increasingly popular as a method for treating municipal solid waste (MSW). Whilst this process can separate many recyclates from mixed waste, the resultant organic residue can contain high levels of heavy metals and physical and biological contaminants. This review assesses the potential end uses and sustainable markets for this organic residue. Critical evaluation reveals that the best option for using this organic resource is in land remediation and restoration schemes. For example, application of MSW-derived composts at acidic heavy metal contaminated sites has ameliorated soil pollution with minimal risk. We conclude that although MSW-derived composts are of low value, they still represent a valuable resource particularly for use in post-industrial environments. A holistic view should be taken when regulating the use of such composts, taking into account the specific situation of application and the environmental pitfalls of alternative disposal routes.     

Incorporating natural regeneration in forest landscape restoration in tropical regions: synthesis and key research gaps

Extensive tropical forest loss and degradation have stimulated increasing awareness at the international policy level of the need to undertake large‐scale forest landscape restoration (FLR). Natural regeneration offers a cost‐effective way to achieve large‐scale FLR, but is often overlooked in favor of tree plantations. The studies presented in this special issue show how natural regeneration can become an important part of FLR and highlight the ecological, environmental, and social factors that must be considered to effectively do so. They also identify major knowledge gaps and outline a research agenda to support the use of natural regeneration in FLR. Six central questions emerge from these studies: (1) What are the ecological, economic, and livelihood outcomes of active and passive restoration interventions?; (2) What are the tradeoffs and synergies among ecological, economic, and livelihood outcomes of natural regeneration, restoration and productive land uses, and how do they evolve in the face of market and climate shocks?; (3) What diagnostic tools are needed to identify and map target areas for natural regeneration?; (4) How should spatial prioritization frameworks incorporate natural regeneration into FLR?; (5) What legal frameworks and governance structures are best suited to encourage natural regeneration and how do they change across regions and landscapes?; (6) What financial mechanisms can foster low‐cost natural regeneration? Natural regeneration is not a panacea to solve tensions and conflicts over land use, but it can be advantageous under some circumstances. Identifying under what conditions this is the case is an important avenue for future research.     

Rehabilitation of Tropical Lands: A Key to Sustaining Development

Land rehabilitation is proposed as a management strategy to reverse the negative consequences of tropical deforestation and land degradation. We first define the concepts associated with ecosystem modification—conversion, damage, and degradation—and those associated with ecosystem repair—restoration, rehabilitation, and reclamation. We then present a scheme of sustainable land use in the tropics, with illustrations of how rehabilitation and restoration activities fit into the overall scheme of the use of land. Because damaged lands cannot contribute effectively to sustained economic development, land rehabilitation is a necessary step for increasing the chances of attaining sustainability. Approaches for rehabilitating ecosystems are discussed, including the management of stressors and subsidies in relation to their point of interaction in the ecosystem. Finally, we illustrate the concepts of ecosystem rehabilitation of damaged, degraded, and derelict lands with examples of case studies from dry to humid life zones in island and continental situations throughout the tropics. The case studies demonstrate that opportunities for success exist, even with severely degraded lands, but a considerable amount of research remains to be done before we have a full understanding of the complexity of the task facing us.     

Conservation planning and Indigenous governance in Australia's Indigenous Protected Areas

Indigenous Protected Areas (IPAs) recognize that “country” constitutes land and waters that have enduring cultural, social, and economic linkages for Aboriginal and Torres Strait Islander peoples that extend over millennia, and which are critical to sustainable Indigenous futures. Within Australia's conservation system, IPAs become part of the National Reserve System (NRS) when Indigenous peoples voluntarily announce their intention to manage “country,” in accordance with their law, custom, and culture, and consistently with national and international conservation guidelines. The NRS requirement is that land is managed “in perpetuity” which highlights a potential tension between with the conservation goals and the voluntary character of IPAs. Ecological restoration in IPAs also raises contested ideas about what is “natural,” the relevant “baseline” for restoration, and what are the objectives to be achieved—ecological or cultural sustainability? Experience from Healthy Country Planning in IPAs indicates that restoration of traditional owner decision‐making, as well as respectful use and valuing community knowledge, is central to the sustainability of outcomes. Ecological restoration is most effectively achieved by restoring governance processes that support Indigenous peoples given the inseparability of cultural, social, economic, and ecological objectives.     

基于文献计量的细菌-生物炭协同修复重金属污染土壤研究进展

为提高重金属污染土壤可持续修复效能,研究生物炭与细菌对重金属污染土壤的协同修复作用。基于文献计量学分析及重金属污染土壤修复背景,总结了细菌与生物炭对土壤重金属的稳定化特征及菌炭间的相互作用,分析了单一生物炭或细菌对重金属污染土壤修复的局限性,强调了细菌-生物炭协同修复技术的优势,阐述了细菌与生物炭主要通过离子交换、固定作用、氧化还原作用和迁移作用等重要机制有效修复重金属污染土壤,揭示了细菌-生物炭协同作用在重金属污染土壤修复中的巨大应用价值。文献计量学研究表明,生物炭与细菌对重金属污染土壤的协同修复已得到广泛关注。目前认为:生物炭与细菌的协同作用可有效改良土壤理化性质及提高土壤修复效率,也可促进植物生长及植物修复进程;生物炭对细菌影响具有双重性质,可促进细菌生长,也可能对细菌产生毒害;细菌可改变生物炭的理化性质,进而强化生物炭的重金属固定性能;细菌协同生物炭联合修复重金属污染土壤过程中,生物炭主导吸附和固定,细菌则发挥活化和解毒等功能;优化细菌-生物炭组合形式,发展混合细菌与多种类生物炭协同技术,是复合重金属污染土壤可持续修复亟待解决的重要问题;进一步揭示细菌与生物炭对重金属污染土壤的耦合作用及长效作用机制,规避生物炭生产和应用中的潜在生态健康风险,研发新型高效能细菌与生物炭复合体是细菌协同生物炭可持续修复重金属污染土壤应用领域面临的挑战。     

Differences in stakeholder perceptions about native forest: implications for developing a restoration program

Ecological restoration is a global priority. Incorporating stakeholders' perceptions has been established as a critical factor to improve the success of restoration and conservation initiatives and decrease future social conflicts; however, it has barely been incorporated. Our objective was to analyze and compare the differences in the perceptions of Chilean dryland forest restoration of three groups: local community, experts, and government managers. We asked about: (1) what is the knowledge, importance, and uses that they have and give to the native forest and its restoration? (2) What is the willingness to restore the native forest? (3) What are the most valuable goods and services provided by the forest? (4) Where to begin to restore? (5) What criteria must be considered to prioritize areas to restore? To determine if the criteria selected were related to the stakeholder group, a semi‐parametric multivariate analysis of variance (MANOVA) was performed. Semi‐structured interviews were carried out with 61 stakeholders. The community gave greater importance to restoring the ravines and creeks, the experts to restoring areas that increase landscape connectivity, and both experts and government managers to restoring areas of greater biodiversity and ecological value. The experts gave a lower value to both social and economic criteria compared to the local community and government managers. The differences among stakeholder perceptions must necessarily be considered in the restoration programs. Research on perceptions can contribute to decision‐making and will favor the social approval and long‐term success of restoration programs.     

Plants as extreme environments? Ni-resistant bacteria and Ni-hyperaccumulators of serpentine flora

During recent years there has been an increasing interest in the bacterial communities occurring in unusual, often extreme, environments. On serpentine outcrops around the world, a high diversity of plant species showing the peculiar features of metal hyperaccumulation is present. These metal hyperaccumulators have received much attention for their potential biotechnological exploitation in phytoremediation processes, but also as unusual, extreme habitats for the associated bacterial flora, which could reveal novel details concerning bacterial adaptation. This paper will briefly focus on the research topics that have been addressed to date on bacteria associated with serpentine plants and aims to provide a state of the art and to present possible future directions for research which could lead to new insights on microbial adaptation and evolution, and potentially applied in technologies for sustainable use and remediation of contaminated land.     

Utilization of Grasses for Potential Biofuel Production and Phytoremediation of Heavy Metal Contaminated Soils

This research focuses on investigating the use of common biofuel grasses to assess their potential as agents of long-term remediation of contaminated soils using lead as a model heavy metal ion. We present evidence demonstrating that switch grass and Timothy grass may be potentially useful for long-term phytoremediation of heavy metal contaminated soils and describe novel techniques to track and remove contaminants from inception to useful product. Enzymatic digestion and thermochemical approaches are being used to convert this lignocellulosic feedstock into useful product (sugars, ethanol, biocrude oil + biochar). Preliminary studies on enzymatic hydrolysis and fast pyrolysis of the Switchgrass materials that were grown in heavy metal contaminated soil and non-contaminated soils show that the presence of lead in the Switchgrass material feedstock does not adversely affect the outcomes of the conversion processes. These results indicate that the modest levels of contaminant uptake allow these grass species to serve as phytoremediation agents as well as feedstocks for biofuel production in areas degraded by industrial pollution.     

Ecology and Hybridization Potential of Two Sympatric Metallophytes,the Narrow Endemic Crepidorhopalon perennis (Linderniaceae) and its More Widespread Congener C. tenuis

Crepidorhopalon perennis is a metallophyte critically endangered by mining activities and currently known from only one site on copper‐rich soils in Katanga (Dem. Rep. Congo). It is closely related to the annual C. tenuis, also a rare metallophyte, but with a broader geographical range. We investigated the variation in morphometric traits and ecological niches (based on edaphic conditions and pollinator assemblages) of C. perennis and C. tenuis, to evaluate the risk of inter‐specific competition, and their potential for hybridization to ascertain if C. perennis might be at risk of genetic swamping by its more widespread congener. We examined whether species were found under sympatric or parapatric settings with opportunity for hybridization (or gene exchange). Such knowledge is essential for implementing restoration management protocols, including the introduction of C. perennis into substitution sites where C. tenuis might be already present. Fourteen morphological characters and 11 soil variables were measured and visiting pollinator species were identified at the site where the two species co‐occur. Our results show that the two species can be distinguished based on their morphological traits, show niche overlap based on edaphic properties, and share the same pollinator assemblage. In addition, no morphologically intermediate individuals could be detected, suggesting no hybridization, and that the two species may be reproductively isolated. We conclude that C. perennis conservation and restoration operations can be realized in substitution sites where C. tenuis may be present, with the need, however, to evaluate the potential effect of sharing a pollinator assemblage on reproductive success of both species.     

Some issues and options for the conservation of native biodiversity in rural New Zealand

Summary For the 70% of New Zealand under private ownership, native biodiversity conservation has to occur within a landscape that must also provide a productive return to land owners. Recent New Zealand legislation, especially the Resource Management Act 1991, promotes sustainable management on private land by allowing for the economic and cultural well-being of local communities while providing for the protection of natural resources including native biodiversity. We suggest that, to effectively conserve native biodiversity in rural landscapes, we need to consider four key issues: (i) what might be realistic goals for native biodiversity conservation; (ii) how might we better arrange different land uses to meet both native biodiversity and production goals; (iii) what is the optimum arrangement of native biodiversity; and (iv) how native biodiversity conservation can improve productive returns to land managers. Options to enhance native biodiversity conservation include a variety of incentives (e.g. management agreements, financial incentives and regulatory systems) and onsite management options (e.g. remnant management, restoration plantings, weed and pest control, use of native species for commercial and amenity purposes, use of exotic species to facilitate native biodiversity). The importance of taking a landscape-based rather than a paddock-based approach to management is emphasized.