Synergistic impact of Rhizobium and arbuscular mycorrhizal fungi on lentil plant tolerance to heavy metal-rich fly ash amended soil

Abstract The purpose of the study was to investigate the impact of microbes [symbiotic bacteria viz. Rhizobium (Frank) and the arbuscular mycorrhizal fungi (AMF) viz. Funneliformis caledonius (Nicolson & Gerd.) and Glomus bagyarajii Mehrotra] on the growth and physiology of lentil (Lens culinaris Medik.) cultivated in soil alone and soil amended with fly ash. The experiment had twenty-four treatments, twelve in sterilized soil and twelve in unsterilized soil (with six treatments in soil alone and six in soil amended with fly ash in both the sets). Amendment of soil with 25% fly ash significantly increased plant growth. Microbial inoculation further increased the plant growth and physiological parameters studied (plant length, fresh and dry weight, chlorophyll and protein content, and nitrate reductase activity). Microbial parameters like nodule number and fresh weight, mycorrhizal root colonization and spore numbers were also significantly higher in plants inoculated with Rhizobium + AMF. Soil amendment with 25% fly ash together with inoculation of Rhizobium + AMF further improved the growth of lentil. Plant heavy metal (Cd, Pb, Zn) content was significantly more in soil amended with fly ash, but microbial inoculation significantly decreased heavy metal uptake. Of the two AM fungus studied F. caledonius proved to be better, resulting in higher plant growth and physiological parameters studied with reduced heavy metal uptake.