Heavy metals (HMs) in soil, air, and water environments effect human health. These HMs cannot be degraded in soil and they can only be transformed from one state to another. Food and energy resources such as coal, oil, petrol, etc. are gradually diminishing due to ever increasing demand and consumption, world faces crisis. There is an urgent need to address these problems by reclaiming the waste/polluted land for food and energy production. Various physicochemical remediation strategies are being proposed, developed, and tested but they are all very costly and only applicable to small contaminated sites. During the past two decades or so, plant-based phytoremediation technology is rapidly evolving as a promising new tool to address the issue with the potential to remediate HM contaminated soils in a sustainable manner. Plants, labeled as phyto-tolerant or phyto-accumulators, surviving on such contaminated soils reduce the toxicity by preventing their translocation or destroying the contaminants by sequestration by synthesizing thiol-containing HM-binding proteins (nano-molecules) and peptides (phytochelators or PCs) which modulate internal levels of metal concentration between deficient and toxic levels. But such plants are very slow growing, producing small biomass, and the process taking a long time to effectively remediate such soils. To overcome limitations of using such plants, plants capable of high biomass production and tolerating multiple HMs, such as non-food bioenergy crops (Vetiver and Hamp), are required. This plant-based remediation strategy can further be enhanced with the use of both plants and rhizosphere microbes like arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria. The combination of three components, i.e. high biomass producing plant, soil, and its rhizosphere harboring plant growth-promoting rhizobial (PGPR) microbiota, particularly AMF, will further improve the process of nano-phytoremediation of HM contaminated soils. This mini review focuses on how phytoremediation, nanotechnology, AMF and PGPR technologies can be merged together to form an integrated nano-mycorrhizo-phytoremediation (NMPR) strategy which synergistically achieve the goal of remediation of soil contaminants and improve the phytoremediation performance of bioenergy plants grown on HM polluted soils. This review also identifies the urgent need to conduct field-scale application of this strategy and use it as potential tool for reestablishing plant cover and population diversity during restoration of derelict land post-industrial/mining activities.

Mycorrhizas in the Perennial Grasses of Cholistan Desert, Pakistan

There is growing concern for the contamination of our soils and waters worldwide with heavy metals (HMs), as a result of indiscriminate use of agrochemicals for feeding growing population which require optimal use of resources and sustainable agricultural strategies. This can be simultaneously achieved by using microbes as bio-fertilizers, bio-protectants, and bio-stimulants, and suitable phytoremediation- plant capable of removing heavy metals contaminants from contaminated sites. There is a growing need to adopt such environmentally safe, attractive, and economical techniques that can remove most HMs contaminants as well as yield high biomass for bioenergy production. Phytoremediation and the microbes associated with the roots and inhabiting rhizospheres of the plants used for this purpose, has emerged as an alternative strategy. This article reviews the principles and application of this strategy, and provides an overview of the use of fast growing, non-food bioenergy plants, like Vetiver grass and industrial hemp, and their root-associated microbiota such as Arbuscular Mycorrhizal Fungi (AMF), Mycorrhiza Helping Bacteria (MHB), and Plant-Growth-Promoting-Rhizobia (PGPR) that can both tolerate and immobilize HMs in the roots, i.e. sequestrate contaminant HMs thereby protecting plants from metal toxicity. This mini-review also focuses on other phytoextraction strategies involving rhizosphere microbes, such as (1) inoculating plants used for phytoremediation of HMs contaminated soil and water with rhizobial microflora, and (2) managing their population in the rhizospheres by using a consortium of site specific AMF, PGPR, and MHB, and N-fixing rhizobia as biofertilizers to Phyto-remediate derelict contaminated sites. Various crop management strategies such as Crop Sequencing and Intercropping or Co-cropping of, for example, mycorrhizal and non-mycorrhizal crops, or leguminous and non-leguminous crops, etc., can be employed for improved plant growth. Another possible strategy to exploit soil microbes is to employ pre-cropping with mycotrophic crops to exploit AMF for mycorrhizo-remediation strategy.

Wetlands and aquatic ecosystems, which are an important part of the ecological system and national resources that need to be well managed, are becoming polluted by toxic heavy metals (HMs) from the industrial mining and smelting of metalliferous ores, and agricultural activities. The loss of wetlands may cause a loss of flora and fauna and thereby decrease biodiversity. Waterlogging resistant plants, their root associated microbes (Arbuscular Mycorrhizal Fungi (AMF)) and plant growth promoting rhizobia (PGPR) can provide potential tools in constructed wetlands (CWs) in order to allow for the Nano-Mycorrhizo-Phytoremediation (NMPR) of HM-polluted natural wetlands and aquatic ecosystems. AMF-CW systems should be considered ideal locations for the technical installations for phytoremediation and need to be optimized for the efficient functioning of phytoremediation in field trials. This presentation will address one of the major hurdles in the production of large quantities of indigenous and stress-adapted AMF inoculum for the purposes of constructing artificial AM-CW systems. The significance and potential role of floating islands of aquatic macrophytes such as Vetiver grass and their root associated microbes (AMF and PGPR) in an environmental cleanup of HM contaminated industrial, municipal, and mining effluents, will be highlighted in the presentation. During the environmental and pollutant stresses, the aquatic macrophytes and their root associated microbes produce nano-molecules of HM-binding cysteine-rich peptides, phytochelators (nano-molecules) forming HM-complexes that sequester HM-ions, protecting the host from contaminants. HM-adapted AMF not only enhance Vetiver grass growth, producing a greater biomass for bio energy production, but also uptake/stabilize HMs, e.g., Nano-Mycorrhizo-Phytoremediation (NMPR).