Biochar related treatments improved physiological performance, growth and productivity of Mentha crispa L. plants under fluoride and cadmium toxicities

Abstract

Modification of biochar with chemical reagents is an effort to increase the efficiency of this organic material to adsorb environmental pollutants. Typically, these chemically modified materials have special structural specifications that allow the adsorption and stabilization of high levels of environmental pollutants. Therefore, this research was carried out to assess the possible effects of solid and chemically engineered biochars (non-biochar, solid biochar, modified biochar with H2O2, KOH, and H3PO4) on reducing fluoride and cadmium toxicities (non-toxic, 600 mg NaF kg−1 soil, 60 mg Cd kg−1 soil and 600 mg NaF kg−1 soil + 60 mg Cd kg−1) in mint plants (Mentha crispa L.). The application rate of biochar and modified biochars was 25 g kg−1 soil. The addition of biochar and especially engineered biochars to the soil reduced the availability of fluoride and cadmium to the plants. Biochar and chemically modified biochars increased soil cation exchange capacity (CEC) (up to 31%), pH (up to 11%), leaf area (up to 22%), chlorophyll content index (up to 19%), maximum efficiency of photosystem II (up to 32%), biomass (up to 21%) and essential oil production (up to 28%) in mint plants. On the other hand, biochar-related treatments reduced the reactive oxygen species generation, antioxidant enzymes activities, and lipid peroxidation in the root (up to 41%) and leaf tissues (up to 40%). In general, modified biochars showed a better effect than solid biochar in reducing fluoride and cadmium toxicities. The H3PO4-modified biochar was a bit more successful than other biochar-related treatments in increasing mint performance under fluoride and cadmium toxicities. Therefore, the chemically engineered biochars are the superior treatments to improve mint growth and productivity under fluoride and cadmium toxicities, because of their excellent physicochemical specifications such as high level of CEC, functional groups, and specific surface area.