Application of plant growth-promoting rhizobacteria (PGPR) associated with energy plant, Pennisetum purpurenum, in cadmium and zinc contaminated soil

Abstract

Heavy metal contamination of soil and water causes environmental problems by inhibiting plant growth and harming microbial communities. Cooperative interactions between plants and bacteria can promote the growth and survival of the two taxa in harsh environments. Plants have been shown to secrete nutrients for enhancing growth of certain bacteria. In return, these bacteria chelate toxic metals, dissolve minerals, produce auxin, or even fix nitrogen for plants. Our work explored the interactions between economically important plants and a bacterial community with potential to be a biofertilizer for cadmium contaminated areas. Experiments were performed in a greenhouse under controlled conditions. Three Napier grass (Pennisetum purpurenum) variants (Pak Chong 1, King Grass, and Emperor) were planted with the addition of selected microbial species, Klebsiella huaxiensis and Pantoea cypripedii, in contaminated soil from an agricultural area in Mae Sot District, Tak Province, Thailand. Each plant variant was separated into three groups; control, plants with P. cypripedii (Pc), and plants with K. huaxiensis (Kh). Solutions containing cadmium and zinc were added to each pot daily to simulate conditions at a contaminated site. After 60 days, Pc and Kh groups of all Napeir grass variants showed significantly higher plant growths than the controls. Total Cd uptakes of PCPc, PCKh, and KGPc were significantly higher than those in control groups, while Zn uptakes were significantly higher in KG and EM plants with the addition of Pc and Kh than other treatments. Growing Napier grass with the addition of Pc or Kh as biofertilizer in the cadmium and zinc contaminated agricultural area in Mae Sot District, Tak Province could be considered for high biomass production. Future field experiments for greater understanding of the heavy metal uptake and development of sustainable solutions are recommended.