Lonicera japonica Thunb. growth and its rhizosphere environment characteristics with application of plant growth-promoting Rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) are beneficial native soil bacteria that colonize the rhizosphere or plant roots and regulate the functional properties of agricultural systems. One of the proposed mechanisms through which PGPR enhances plant growth is the production of plant growth regulators, especially cytokinin. However, little information is available regarding cytokinin-producing PGPR inoculation on growth and water stress consistence of Lonicera japonica Thunb. seedlings. Therefore, a bacterial strain with high cytokinin production and known positive effects on plant growth was selected for use in present investigation. Cross-linked polyacrylamide is a widely studied super-absorbent polymer with segments of hydrophilic groups that can absorb and retain liquids, with the absorbed water it is difficult to remove even under pressure. In addition, because of the water absorbing properties of these macromolecules, cross-linked polyacrylamide were used in a wide range of applications in agriculture and forestry. Firstly, an inoculation experiment was conducted to determine whether cross-linked polyacrylamide could be used as carrier for PGPR by inoculating Bacillus cereus DZ1. And then, a Lonicera japonica Thunb. afforestation experiment, including five treatments, i.e. PGPR (B. subtilis DZ1 inoculation alone), CLP (cross-linked polyacrylamide was applied alone), C-P (B. subtilis inoculation with CLP), CPG (gel was made of PGPR and CLP), and CK (neither B. subtilis nor CLP was applied) was conducted. The experiment was to evaluate the effect of different ways of PGPR application on Lonicera japonica Thunb. growth and microbial characteristics in rhizosphere soils. Results indicated that compared with the diluted water treatment, the number of effective viable bacteria of bean sprout juice dilution treatment in cross-linked polyacrylamide was significantly increased by 19.45%~664.05%, which meant that CLP can be used as an carrier for B. subtilis DZ1. The root exudates, namely amino acids, organic acids and total sugars in CPG treated Lonicera japonica Thunb. rhizosphere soils were significantly increased by 37.36%, 30.04% and 8.18% than those in PGPR treatment. Although B. subtilis DZ1 inoculation alone had no significant effect on microbial biomass carbon contents, the CPG treatment evidently increased microbial biomass carbon and significantly enhanced microbial respiration, showing 18.02%, 9.93%, 8.56% and 18.91% increases in microbial respiration rate over the treatments of PGPR, CLP, C-P and CK, respectively. At the same time, the metabolic quotient was reduced by the CPG treatment, demonstrating 12.74%, 7.62%, 8.02% and 14.02% decreases, respectively. Besides, the CPG treatment achieved the highest Simpson index, however the lowest Shannon and McIntosh index among all the treatments. CPG treatment had no significant effect on afforestation survival rate, it was beneficial to the shoot and root dry matter accumulation of Lonicera japonica Thunb. Compared with C-P treatment, CPG treatment increased the relative water content of Lonicera japonica Thunb. leaves by 10.34%, whereas decreased the relative electric conductance by 9.70%. As a result, the CLP-PGPR gel can alleviate the drought stress and interfere with the suppression of plant growth through regulating the micro ecological environment of Lonicera japonica Thunb. rhizosphere soil, showing a real potential to perform as a drought stress inhibitor in arid environments. © 2016, Chinese Society of Agricultural Machinery. All right reserved.