Rhizosphere Microbial Communities and Heavy Metals

Abstract

The rhizosphere is a microhabitat where there is an intense chemical dialogue between plants and microorganisms. The two coexist and develop synergistic actions, which can promote plants’ functions and productivity, but also their capacity to respond to stress conditions, including heavy metal (HM) contamination. If HMs are present in soils used for agriculture, there is a risk of metal uptake by edible plants with subsequent bioaccumulation in humans and animals and detrimental consequences for their health. Plant productivity can also be negatively affected. Many bacteria have defensive mechanisms for resisting heavy metals and, through various complex processes, can improve plant response to HM stress. Bacteria-plant synergic interactions in the rhizosphere, as a homeostatic ecosystem response to HM disturbance, are common in soil. However, this is hard to achieve in agroecosystems managed with traditional practices, because concentrating on maximizing crop yield does not make it possible to establish rhizosphere interactions. Improving knowledge of the complex interactions mediated by plant exudates and secondary metabolites can lead to nature-based solutions for plant health in HM contaminated soils. This paper reports the main ecotoxicological effects of HMs and the various compounds (including several secondary metabolites) produced by plant-microorganism holobionts for removing, immobilizing and containing toxic elements.

“Breeding on Mountains” Resulted in the Reorganization of Endophytic Fungi in Asexually Propagated Plants (Ligusticum chuanxiong Hort.)

“…In this study, LZ showed a richer diversity of endophytic fungi than CX. On the one hand, the soil environment (including microorganisms and physiographical factors) of L. chuanxiong can be changed, and the endophytic fungi will be reshuffled because of the transplantation ( Caracciolo and Terenzi, 2021 ). On the other hand, the relative abundance of some endophytic fungi showed regular changes with plant transplantation and finally existed stably in specific growth stages of L. chuanxiong ( Zhalnina et al, 2018 ).…”

“…Ecosystems based in the soil microbiome are influenced and controlled by multiple abiotic and environmental factors, such as soil structure and type, soil pH, soil nutrients, geographical factors (altitude, latitude, and longitude), climatic factors (UV radiation, CO 2 , and temperature) ( Islam et al, 2020 ). Abiotic and environmental factors result in the establishment of multiple microenvironments that offer a diversity of ecological niches ( Caracciolo and Terenzi, 2021 ). In the previous experiments, we found that the diversity of species, main ecological functional groups, and differences in production areas of the fungal community showed a gradual change pattern between the non-rhizosphere soil, the rhizosphere soil, and the rhizome of L. chuanxiong , which proved that during the cultivation process, plants obtain part of the species from the soil of the production area and accumulate or subtract continuously to form a specific endophytic flora ( Zhang et al, 2021 ).…”

“…In the rhizosphere, plants release root exudates, which promote microorganism population development. The rhizosphere offers varieties of carbon-rich micro-habitats, and beneficial microorganism populations can colonize by using such substrates ( Caracciolo and Terenzi, 2021 ). Plants contribute to the assemblage of their rhizobiome ( Mercado-Blanco et al, 2018 ; Sasse et al, 2018 ; Poveda et al, 2020 ), and some plant species can have their specific microbial community ( Mhlongo et al, 2018 ), which can, in turn, change during their growing stage, and in different root regions, the results of the LZ(CX) rhizosphere fungal communities tending to be similar in this study are consistent with this view.…”

“…We analyzed differences in the community structure of endophytic fungi during the three cultivation cycles and verified the results of two matches of control breeding experiments and through the result of the fungal isolation experiment of the control experiment and the result of the pot experiment to verify the feedback of endophytic fungi to its host. The scientific mechanism behind transplanting in vegetative reproduction is expected to be explored, which provides a scientific reference for slowing down the complications of other economic plants in asexual reproduction and maintaining the quality of economic plants ( Caracciolo and Terenzi, 2021 ).…”

A review of advances in bioremediation of heavy metals by microbes and plants

“…Contaminated land is a potential threat to human health, and its continual discovery over recent years has led to international efforts to remedy many of the sites, either as a response to the risk of adverse health or environmental effects caused by contamination or to enable the site to be redeveloped for new use (Maheshwari et al, 2014, Damodaran andSuresh, 2011). In this context, bioremediation process is reported to be an important strategy for the removal of the heavy metal from the environment, where living part can be considered as a solar-driven pump, which can extract toxic elements from the contaminated soil (Caracciolo andTerenzi, 2021, Ojuederie and. Briefly, the present article offers an overview and discusses the heavy metal toxicity, metal-microbes interactions, and mechanisms used by plants and microbes for remediation of heavy metals pollutants.…”