Silicon Amendment Reduces Soil Cd Availability and Cd Uptake of Two Pennisetum Species

Abstract

Silicon (Si) plays important roles in alleviating heavy metal stress, but the migrating effects and mechanisms, especially for Pennisetum, are not well studied. In this study, Pennisetum glaucum and Pennisetum glaucum × P. purpureum were used to explore the impacts of Si application on alleviating cadmium (Cd) toxicity and its possible mechanism. Treatments consist of four levels of Cd (0, 10, 50, and 100 mg·kg−1) with or without 2.0 mM Si amendments. Under Cd stress, Si application significantly increased plant biomass and Si content, reduced Cd content, and decreased the enrichment factor in shoots and roots. Si treatment also increased soil pH and soil residual Cd, while reducing available/oxidizable/reducible Cd content in soil at 50 and 100 mg·kg−1 Cd levels, thereby leading to a reduction of the soil’s available Cd. These findings indicate that Si application is effective in alleviating Cd phytotoxicity of Pennisetum, mainly through reducing plant Cd uptake and increasing soil pH and Cd immobilization, thereby reducing Cd bioavailability.

Cadmium Uptake by Wheat (Triticum aestivum L.): An Overview

“…Cadmium has high assimilability and mobility; thus, its entry into plants is possible through the roots, and it is translocated to shoots in an ionic form in the xylem and phloem over transporters and transpiration [2]. Cadmium can enter the xylem via symplastic transport and possibly through apoplastic transport under high exposure [37].…”

“…The Si can enhance seedling biomass and reduce metal concentration in the shoots and roots of plant seedlings and the xylem sap flow [77]. Dong et al [2] reported that Si utilization remarkably decreases available/oxidizable Cd in soil at 50 and 100 mg/Kg Cd levels. Naeem et al [78] reported that Si application might reduce the Cd contents in wheat by 28%.…”

“…The Si could alleviate the toxic effects of toxic metal elements on plants via external and internal mechanisms. External mechanisms comprise affecting the pH and decreasing the availability of toxic metal elements in soil, whereas internal mechanisms comprise affecting plant uptake, binding toxic metal elements in the cell walls, limiting the transport of toxic metal elements in plants, regulating protein and gene expression, and improving the defense system [2].…”

“…Heavy metal contamination is not only a threat to living organisms but also a global environmental concern [1]. Cadmium is generally released from industrial activities, such as refining, mining, and plastic manufacturing [2]. In addition, Cd is persistent and remains in the environment for decades [3].…”

Silicon and Its Application Methods Improve Physiological Traits and Antioxidants in Triticum aestivum (L.) Under Cadmium Stress

“…Another group of researchers who used Si as root application reported that Si in root application could alleviate heavy metal (HM) stress more efficiently than Si foliar-application due to (1) decreased HM absorption from roots to shoots (Dong et al 2019), (2) enhanced HM binding with root cell walls and delimited their apoplastic transport (Huang et al 2018), and (3) coprecipitate with HMs to minimize biological active HM concentration in soil (Lu et al 2017).…”