Characterizations of three diazotrophic Paenibacillus spp. and their effect on Chinese pakchoi yield and soil enzyme activities

Abstract

ObjectiveNitrogen-fixing (diazotrophic) bacteria are considered possible alternative to nitrogen fertilizers for promoting plant growth and yield. This study was to run a phylogenetic analysis and determine the PGPR traits of the isolated diazotrophic bacteria and characterize the effect of diazotrophic bacteria on Chinese pakchoi yield and soil enzyme activities. MethodsWe isolated 30 diazotrophic bacteria from rhizosphere of wheat (11 isolates), Chinese pakchoi (16 isolates), and lotus (3 isolates) on N-free medium plates. Based on 16S rRNA sequence analysis, the dominant diazotrophic bacteria of wheat, Chinese pakchoi, and lotus belonged to the genus Paenibacillus. ResultsThree multi-function diazotrophic bacteria designated as Paenibacillus spp. P-4, W-7 and L-3 were screened from these 30 diazotrophic. The nitrogenase activities of P-4, W-7 and L-3 were higher than the that of Azotobacter chroococcum used as the control. Strains P-4, W-7 and L-3 can inhibit the growth of two or three plant pathogens of Sclerotinia sclerotiorum, Gibberella zeae and Verticillium dahliae. Strain W-7 has also the phosphate solubilizing ability. Inoculation with Paenibacillus spp. W-7 or L-3 significantly increased the shoot fresh weight of Chinese pakchoi and changed the activity of soil sucrase, phosphatase, and catalase under field conditions, whereas inoculation with Paenibacillus sp. P-4 had no significant effect on plant growth or enzyme activity. ConclusionPaenibacillus sp. W-7 and L-3 have good potential to promote plant yield and improve soil quality.