Plant Growth Promoting Rhizobacteria Enhance Plant Drought Tolerance By Changing Soil Physical and Hydrological Properties.

Increasing global population results in unprecedented demand on agriculture for food. A key challenge our agriculture facing is water shortage and degradation. In this case, developing novel solutions for plant growth under restricted water availability is significant. Plant-growth promoting rhizobacteria (PGPR) had been widely studied as they can benefit plants by increase nutrient uptake, disease protection, ect. However, previous studies mostly focused on bacteria or the interaction between plant and bacteria, little is known how they can modify soil properties. We found that UD1022, a B. subtilis strain could increase plant drought tolerance. The soil water characteristic curves obtained by Hyprop indicate that UD1022 treated samples have greater water retention and lower hydraulic conductivity. The cumulative evaporation of UD1022 treated samples are lower than controls as well. The SEM images showed that UD1022 treated soil samples are more aggregated, and formed biofilms. The possible explanation is the production of extracellular polymeric substances (EPS) by UD1022. EPS would form biofilms, enhancing soil aggregate formation, improve soil structure, and finally increasing water retention. We will further extract and quantify EPS in soil samples treated with UD1022 and its known EPS mutant, as well as in control samples. The neutron radiography images revealed the water distribution in UD1022-treated samples and controls, which provide more visual and direct evidence of soil physical and hydrological properties changed by UD1022. We will also use A. thaliana (Col-0) as a model plant to study the bacterial effect on water distribution in rhizosphere soil and plant root in situ using neutron radiography as both soil matrix and cultivable microbiomes analysis influencing root growth and physiology have been standardized.