Effects of Enterobacter sp. and Pseudomonas sp. inoculation on root microenvironment of alfalfa seedlings under drought stress

Objective The purpose of this study was to explore the mechanism of plant growth promoting rhizobacteria (PGPR) promoting plant growth and enhancing plant drought resistance from the perspective of soil microecology.

Method Enterobacter sp. (D1) and Pseudomonas sp. (D2) with multiple stress resistance and growth promoting potential were selected as test strains, the effects of single inoculant D1, D2 and compound inoculant F on the physical and chemical properties, enzyme activities of alfalfa rhizosphere soil, rhizobacteria and endophytes diversity and community structure under drought stress were analyzed through alfalfa pot experiment.

Result (1) Compared with control, alfalfa seedling biomass in the inoculated group increased significantly, pH and conductivity of rhizosphere soil decreased significantly, and the soil water content and available phosphorus content increased significantly (P < 0.05). Soil alkaline phosphatase activities of group D1, D2 and F were significantly increased by 92.26%, 141.67%, and 72.02%, dehydrogenase activities were significantly increased by 116.93%, 201.63% and 110.12%, sucrase activities were significantly increased by 52.54%, 42.80% and 34.43%, urease activities were increased by 54.66%, 33.27% and 121.67%, respectively. (2) Compound inoculant F could significantly alter the bacterial diversity and community structure of alfalfa root system, increase the richness and diversity of rhizospheric and endophytic bacterial communities, and promote the enrichment of Chloroflexia, Arthrobacter and Enterobacter in rhizosphere soil, and enrich Bacteroidetes, Sphingomonas and Enterobacter in the roots. (3) The correlation analysis between soil physicochemical factors and bacterial communities showed that soil water content, available potassium and available phosphorus were main factors affecting the bacterial community of alfalfa roots.

Conclusion Under drought conditions, plant growth promoting rhizobacteria (PGPR) could alleviate the damage of drought to plants and promote plant growth by promoting soil water retention and nutrient transformation, regulating the community composition of root microorganisms, improving rhizosphere soil microenvironment. The effect of compound inoculant(F) is better than that of single inoculant, which has the potential of further development and utilization.