A critical review of the interactions between rhizosphere and biochar during the remediation of metal(loid) contaminated soils

Abstract

Biochar has a large specific surface area, well-developed pore structure, abundant surface functional groups, and superior nutrient supply capacity, which is widely available and environmentally friendly with its advantages in waste resource utilization, heavy metal(loid) remediation, and carbon storage. This review focuses on the interactions between biochar (including raw biochar, functional biochar (modified/ engineered/ designer biochar), and composite biochar) and rhizosphere during the remediation of soil contaminated with heavy metal(loid)s (Pb, As, Cd, Hg, Co, Cu, Ni, Zn, Cr, etc.) and the effects of these interactions on the microbial communities and root exudates (enzymes and low-molecular-weight organic acids (LMWOAs)). In terms of microorganisms, biochar affects the composition, diversity, and structure of microbial communities through the supply of nutrients, provision of microbial colonization sites, immobilization of heavy metal(loid)s, and introduction of exogenous microorganisms. With regard to root exudates, biochar provides electron transfer support between the microorganisms and exudates, regulates the secretion of enzymes to resist the oxidative stress stimulated by heavy metal(loid)s, ameliorates rhizosphere acidification caused by LMWOAs, and promotes the activity of soil enzymes. The roles and mechanisms of biochar on rhizosphere soils are discussed, as well as the challenges of biochar in the remediation of heavy metal(loid)-contaminated soils, and the issues that need to be addressed in future research are foreseen. Graphical Abstract

Progress in Microbial Fertilizer Regulation of Crop Growth and Soil Remediation Research

“…The bioremediation of soil heavy metals primarily occurs through the interaction of inter-root microorganisms with soil physicochemical properties, which in turn regulates plant growth and stimulates the detoxification of heavy metals in the soil [155]. Soil microorganisms secrete metabolites that can release iron carriers and organic acids, which aid in the chelation of soil toxic metal ions and contribute to the adsorption of heavy metals [156]. The EPS produced by PGPR can adsorb some metal ions such as Cu 2+ , Pb 2+ Cr 6+ , etc., and at the same time, it can degrade polycyclic aromatic hydrocarbons (PAHs) and alkane compounds, thus degrading pollutants in the soil [157].…”