Characteristics of endophytic bacteria from Polygonum hydropiper and their use in enhancing P-phytoextraction

Aims Endophytes are significant for their ecological role in plants and potential applications in phytoremediation. Endophytic bacteria with plant-growth-promoting (PGP) characteristics are isolated as inoculants to enhance phytoremediation efficiency; however, few attempts have been made to isolate bacteria from phosphorus (P)-accumulating plants and study their roles in P-phytoextraction. Method Endophytic bacteria of P-accumulating herb Polygonum hydropiper were isolated and identified. The PGP traits including indole-3-acetic acid (IAA), siderophores, phosphate-solubilization etc. were characterized. Some endophytes were selected as the inoculants for a pot experiment in high P soil to investigate their role in P-phytoextraction. Results Thirty-five isolates were tolerant of high P and classified into 10 taxonomic groups. The production of indole-3-acetic acid into IAA acid and siderophores was dependent on strain species. Tricalcium phosphate (TCP)-solubilizing activity of these strains was associated with a decrease of pH but increases of organic acids production, while phytin-solubilizing activity was associated with a decrease of pH but increases of acid and alkaline phosphatase activities. In the six inoculants, five strains promoted stem and leaf growth of Polygonum hydropiper except for SLs08. P. hydropiper with inoculation of SLr02, SLr15, SLs13 and SLs18 showed significantly higher root length and surface area than the control plants. The inoculation with SLr15, SLs13 and SLs18 significantly enhanced stem and leaf P accumulation of P. hydropiper . Conclusions Endophytic bacteria with PGP traits exist in Polygonum hydropiper and strains SLr15, SLs13 and SLs18 greatly promoted plant growth and shoot P accumulation, offering the most potential as PGP inoculants for assisting P. hydropiper in P-phytoextraction.