Bioavailability of Zn from layered double hydroxides: The effects of plant growth-promoting rhizobacteria (PGPR)

Abstract

There is widespread interest in developing layered double hydroxides (LDH) in agricultural applications to supply essential nutrients for plants. The present study sought to gain a better understanding of the specific effects of Zn-Mg-Fe(III)-LDH intercalated with nitrate (LDH-N) and phosphate (LDH-P) anions in the absence and presence of plant growth-promoting rhizobacteria (PGPR) on Zn phyto-availability, using sand culture experiments. The LDH were synthesized and their characteristics were investigated by XRD patterns, FT-IR spectra, and elemental analysis. In the first experiment, predetermined amounts of LDH-N or LDH-P mixed with 500 g sand quartz to provide 0, 5, 15, 25 and 50 mg Zn kg−1 sand. In the second study, the potential of three pseudomonas strains, i.e., pseudomonas sp. A5 (P1), p. putida P19 (P2) and P. fluorescens P52 (P3) (high Zn-solubilizing bacteria) on kinetic release and plant availability of Zn from LDH were investigated in a batch and a pot experiment. The LDH appreciably improved the Zn content of plants, irrespective of the sources applied. However, the concentration and uptake of Zn in root and shoot of maize plants grown in the LDH-N-sand system were higher than those grown in the LDH-P-sand culture. Results of the second experiment showed that, in the LDH-N treatments, all the three pseudomonas strains increased Zn content of roots and shoots. While in the LDH-P treatments, none of the strains had a significant effect on Zn concentrations of root and shoot as compared to the control. According to the results of the batch study, the ability of bacteria in cumulative Zn released increased by increasing the time of incubation. Among three strains, the highest cumulative Zn release from LDH was recorded in the presence of P2, followed by P1 and P3 strains. This study suggested that LDH-N and LDH-P are effective sources for the supply of Zn and improving the growth of maize under Zn deficiency conditions and also highlighted the potential of PGPR to increase Zn availability.