A dynamic rhizosphere interplay between tree roots and soil bacteria under drought stress

Abstract

Root exudates are thought to play an important role in plant-microbial interactions. In return for nutrition, soil bacteria can increase the bioavailability of soil nutrients. However, root exudates typically decrease in situations such as drought, calling into question the efficacy of solvation and bacteria-dependent mineral uptake in such stress. Here we tested the hypothesis of exudate-driven microbial priming on Cupressus saplings grown in forest soil in custom-made rhizotron boxes. A 1-month imposed drought and concomitant inoculations with a mix of Bacillus subtilis and Pseudomonas stutzeri, bacteria species isolated from the forest soil, were applied using factorial design. Direct bacteria counts and visualization by confocal microscopy showed that both bacteria associated with Cupressus Interestingly, root exudation rates increased 2.3-fold with bacteria under drought, as well as irrigation. Forty four metabolites in exudates were significantly different in concentration between irrigated and drought trees, including phenolic acid compounds and quinate. When adding these metabolites as carbon and nitrogen sources to bacterial cultures of both bacterial species, 8 of 9 metabolites stimulated bacterial growth. Importantly, soil phosphorous bioavailability was maintained only in inoculated trees, mitigating drought-induced decrease in leaf phosphorus and iron. Our observations of increased root exudation rate when drought and inoculation regimes were combined, support the idea of root recruitment of beneficial bacteria, especially under water stress.

The effects of drought and inter-plant competition on the ectomycorrhizal interaction between fungi and Aleppo pine seedlings

“…We suggest that the shoot branching mechanism is dependent on the mere presence of the fungi, which might induce a hormonal effect on the shoot branching pattern. For example, production of the growth hormone auxin was connected with EMF colonization in Poplar (Felten et al ., 2009), and cypress saplings exuded auxin when inoculated with rhizosphere bacteria (Oppenheimer-Shaanan et al ., 2022). Moreover, an increase in ABA hormone, which is related to drought tolerance, was seen in redwood seedlings colonized by AMF under drought (Willing, 2019).…”

Application Progress of Culturomics in the Isolated Culture of Rhizobacteria: A Review

“…Moreover, the beneficial interactions between plants and their microbiomes are critical for maintaining normal plant growth and development . Simultaneously, the composition of rhizobacteria communities undergoes dynamic changes, influenced by factors such as plant species, developmental stage, physiological state, and growth environment. − The chemical composition of root secretions may primarily influence rhizobacteria diversity, metabolic activity, and community succession; , however, plant genotypes and soil types are conserved in the reorganization of rhizobacteria communities …”

“…Moreover, the soil is a rich source of diverse microorganisms, particularly rhizobacteria, which interact closely with the plant's root system. 3 Plant root bacteria promote plant growth and development through multiple pathways. 4,5 These pathways include (1) establishing symbiosis with the plant root system, forming nodule structures that enhance soil exposure and improve water and nutrient uptake; (2) inducing the expression of resistance genes to enhance the plant's adaptability to environmental stresses; and (3) revitalizing soil nutrients to enhance the plant's absorption of these nutrients.…”

“…12 Simultaneously, the composition of rhizobacteria communities undergoes dynamic changes, influenced by factors such as plant species, developmental stage, physiological state, and growth environment. 13−15 The chemical composition of root secretions may primarily influence rhizobacteria diversity, metabolic activity, and community succession; 3,16 however, plant genotypes and soil types are conserved in the reorganization of rhizobacteria communities. 8 Information about rhizobacteria is currently obtained through two primary methods: nonculture-dependent and culturedependent.…”

“…Meanwhile, the plant’s aboveground surface is colonized by fewer microorganisms. Moreover, the soil is a rich source of diverse microorganisms, particularly rhizobacteria, which interact closely with the plant’s root system …”