Phytoextraction of Metals: Modeling Root Metal Uptake and Associated Processes

Abstract

IntroductionPhytoextraction is a process which can remove the soluble (bioavailable) metal pool from soil or aqueous solutions using different kinds of terrestrial or aquatic plants. This transport may be divided into three different steps: (1) absorption from the solution (e.g., soil solution), (2) transport to the root xylem, and (3) transport to the shoots (Mench et al. 2009).A modern approach, how to evaluate the extraction potential of selected plants as well as how to plan and design the most effective metal phytoextraction, is the ability to relevantly model this process. There are many studies aimed at the modeling of metal transport. Nevertheless, there is a limited amount of present studies, which are focused on the modeling of the phytoremediation process. In general, developing an applicable model requires sufficient conceptual model description and a fundamental theoretical understanding of the studied system, as well as its experimental equipment and measurement; these are all crucial aspects required to create a relevant simulation of studied problem. This chapter attempts to describe the problems associated with metal phytoextraction modeling. The term "root metal uptake" is crucial for the simulation of phytoremediation of metals, which is a concrete modification of the general term "root uptake." Root uptake is one of the most important processes considered in numerical models because root surfaces represent the first-phase boundaries in nature for nutrients and toxic elements. In order to efficiently model the phytoextraction processes, it is essential to provide information about (1) the spatiotemporal concentration changes of metals in the root-influenced soil and (2) the cumulative uptake of metals per unit length of root over time (Darrah et al. 2006). Root UptakeDetermining water and metal uptake by plant roots and their subsequent translocation into the tissues of the aerial parts is obviously critical for assessing the modeling of phytoremediation options. Because metals are taken up by plants dissolved in water, it is crucial to have information about the transport of water and the hydraulic properties of the roots. Root Water UptakeWater is primarily absorbed by the root hairs and other root zones and then transported to the aerial parts in xylem tissues. Water absorption by the plants is mainly a response to the water potential gradient (from low to high energy) from the rhizosphere to the xylem of the roots. Soil water has a lower total solute concentration than plant water, and hence the osmotic gradient tends to drive water from the soil into the root. The rate of water uptake from the soil depends on rooting density, the hydraulic conductivity of the roots, and the difference between average soil-water suction and root suction. The root hydraulic conductivity is a measure of the amount of water transported by the root in an interval of time at a determinate pressure [mg g et al. 1987). It depends on osmotic potential gradients which result from differences in the composition and t...

Exposure of engineered nanomaterials to plants: Insights into the physiological and biochemical responses-A review

“…Uncoated nFeOx behave similarly to naturally occurring iron-based nanoparticles and agglomerate to a certain degree due to Van der Waals forces and other interactions, forming aggregates too large to be transported within the xylem tissues. Both the nFeOx and their aggregates adhere to the negatively-charged root surface by electrostatic attraction and binding to cation exchange sites (Trakal et al, 2015).…”

“…The effects of nFeOx on plants have been related to particle aggregation on the surface of the roots. The clogging effects of nFeOx reduce the root hydraulic conductivity by inhibiting the adequate water uptake (Ma et al, 2013;Martínez-Fernández et al, 2015). Martínez-Fernández et al (2016a) found a reduction of macronutrients (Ca, K, Mg and S) in l w ' .…”

Lead and copper-induced hormetic effect and toxicity mechanisms in lettuce (Lactuca sativa L.) grown in a contaminated soil

“…This might be related to the different absorption and transport mechanisms of Pb and Cu in lettuce. To our knowledge, soil water with dissolved PTEs can enter up to the parenchyma via the apoplast or enter into the cells via the symplast during the PTEs uptake of plant roots (Trakal et al, 2015). Once in the endodermis, the Casparian strip forces all of the water and PTEs to follow the intracellular pathway (across the plasma membrane) using the active or passive transport systems (Trakal et al, 2015).…”

“…Copper uptake in root cells is passed through the symplast via active and passive transport, while Pb uptake is passed by the apoplastic pathway or via Ca 2+ -permeable channels (i.e., passive transport; Trakal et al, 2015).…”

“…Lettuce is also widely cultivated in China, with a harvested area of 0.65 million hectares (51.1% of the world total) in 2018 (FAOSTAT, 2019). In addition, Cu is an essential element for plant functioning in normal conditions, using active and passive transport systems during uptake, whereas Pb is a highly toxic element without any known essential function in plants, using passive transport systems (e.g., the apoplastic pathway or via Ca 2+ -permeable channels) during uptake (Trakal et al, 2013(Trakal et al, , 2015. Therefore, Pb and Cu are likely to present some specificity in their induced hormetic effect and their toxicity mechanism in lettuce.…”