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

Abstract:

[Objective] Nitrogen-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.[Methods] We 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. [Results] Three 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. [Conclusion] Paenibacillus sp. W-7 and L-3 have good potential to promote plant yield and improve soil quality.