Management of chromium(VI)-contaminated soils through synergistic application of vermicompost, chromate reducing rhizobacteria and Arbuscular mycorrhizal fungi (AMF) reduced plant toxicity and improved yield attributes in Ocimum basilicum L

Abstract

An integrated approach involving vermicompost, chromate reducing bacteria and AMF was tested to manage the toxic impacts of Cr(VI) on Ocimum basilicum as a model plant. Pot experiments were conducted on O. basilicum plants in an artificially Cr(VI)-contaminated soil in two phases of experiment as bioinoculants experiment and vermicompost experiment. In the first phase of the bioinoculants experiment the series of gradient concentrations of Cr(VI) (0, 25, 50 and 100 mg kg^-1 in soil) were evaluated with previously isolated four efficient Cr(VI)-reducing rhizo-bacterial strains (Bacillus Cereus strain SUCR 44, BC; Microbacterium sp. strain SUCR 140, MB; Bacillus thuringiensis strain SUCR186, BT; and Bacillus subtilis strain SUCR188; BS) along with Arbuscular Mycorrhizal Fungus-Glomus fasciculatum (GF) in alone and in co-inoculation form. In the second experiment (vermicompost) the best performing strain (MB) was tested alone or in combination with GF along with different doses of vermicompost. It was observed that vermicompost by itself could be useful in decreasing the bioavailable Cr(VI), uptake of Cr besides improving the nutritional status of plants. The vermicompost also played an important and indirect role and improved herb yield by supporting the multiplication of MB (Microbacterium sp.), an efficient chromate reducing rhizobacteria, that further decreased the bioavailable and toxic form of Cr and improved population and colonization of GF too. The translocation of Cr(VI) was averted through improved colonization of GF, also prevented higher accumulation of Cr in aerial parts (leafy herb) of O. basilicum.

Keywords: Bioavailability; Cr(VI); Cr(VI) reducing bacteria; Glomus fasciculatum; Vermicompost.

Fig. 1

Effect of bioinoculants on (A) root length, (B) plant height, (C) dry root biomass, and (D) dry herb biomass of Ocimum basilicum in graded level of Cr(VI) amended soil (0, 25, 50, 100 mg/kg). Error bars shown as standard error of mean (SE), different letters above the error bars show significant difference at P ≤ 0.05

Fig. 2

Effect of bioinoculants on (A) root length, (B) plant height, (C) dry root biomass, and (D) dry herb biomass of Ocimum basilicum in Cr(VI) amended soil (100 mg kg^–1) with graded level of vermicompost doses (0, 2.5, 5.0 and 10 ton/ha). Error bars shown as standard error of mean (SE), different letters above the error bars show significant difference at P ≤ 0.05

Fig. 3

A Effect of bioinoculants on Cr(VI) bioavailability of Ocimum basilicum in graded level of Cr(VI) amended soil (0, 25, 50, 100 mg/kg). B Effect of bioinoculants on Cr(VI) bioavailability of Ocimum basilicum in Cr(VI) amended soil (100 mg kg^–1) with graded level of vermicompost doses (0, 2.5, 5.0 and 10 ton/ha)

Fig. 4

Effect of bioinoculants on (A) uptake of Cr by root and (B) uptake of Cr by shoot of Ocimum basilicum in graded level of Cr(VI) amended soil (0, 25, 50, 100 mg/kg). Effect of bioinoculants on (C) uptake of Cr by root and (D) uptake of Cr by shoot of Ocimum basilicum in Cr(VI) amended soil (100 mg kg^–1) with graded level of vermicompost doses (0, 2.5, 5.0 and 10 ton/ha). Error bars shown as standard error of mean (SE), different letters above the error bars show significant difference at P ≤ 0.05

Fig. 5

A Effect of bioinoculants on bioaccumulation factor in graded level of Cr(VI) amended soil (0, 25, 50, 100 mg/kg). B Effect of bioinoculants on bioaccumulation factor in Cr(VI) amended soil (100 mg kg^–1) with graded level of vermicompost doses (0, 2.5, 5.0 and 10 ton/ha)

Fig. 6

A Effect of bioinoculants on translocation factor in graded level of Cr(VI) amended soil (0, 25, 50, 100 mg/kg). B Effect of bioinoculants on translocation factor in Cr(VI) amended soil (100 mg kg^–1) with graded level of vermicompost doses (0, 2.5, 5.0 and 10 ton/ha)