Role of Ni-resistant rhizobacteria in the growth and Ni-uptake of maize in a calcareous soil

A pot experiment was conducted to elucidate the effects of single and co-inoculation of maize plant with Bacillus mycoides and Micrococcus roseus, indigenous to HMs contaminated soils, on the plant growth and uptake of essential nutrients and Ni by maize in the soil polluted by 250 and 500 mg Ni kg-1. At each level of Ni contamination, shoot dry weight and nutrients uptake significantly increased in M. roseus and B. mycoides treatments compared to non-inoculated plants. The highest plant growth promoting effect was found for B. mycoides at the level of 250 mg Ni kg-1 and for M. roseus at the level of 500 mg Ni kg-1 which enhanced plant biomass by 33.2% and 90%, respectively, compared to non-inoculated plants. At the levels of 250 and 500 mg Ni kg-1, shoot Ni uptake of plants inoculated with B. mycoides or M. roseus significantly increased compared to non-inoculated plants. Root Ni uptake of plants inoculated with B. mycoides and M. roseus significantly decreased at the level of 250 mg Ni kg-1 and increased at the level of 500 mg Ni kg-1 compared to control plants. The lowest Ni transfer factor and maximum Ni translocation factor were in plants inoculated with B. mycoides at the level of 250 mg Ni kg-1 and in non-inoculated plants at the levels of 500 mg Ni kg-1. Inoculation of plants with B. mycoides and M. roseus may be the effective treatments in Ni phytoextraction at the levels of 250 and 500 mg Ni kg-1, respectively. Consortium of two bacteria had the lowest plant dry matter and shoots and roots Ni uptake and the maximum transfer factor compared to other treatments at the level of 500 mg Ni kg-1 that may be the effective treatment in Ni phytostabilization.