Root exudates and rhizosphere soil bacterial relationships of Nitraria tangutorum are linked to k-strategists bacterial community under salt stress

Abstract

When plants are subjected to various biotic and abiotic stresses, the root system responds actively by secreting different types and amounts of bioactive compounds, while affects the structure of rhizosphere soil bacterial community. Therefore, understanding plant–soil-microbial interactions, especially the strength of microbial interactions, mediated by root exudates is essential. A short-term experiment was conducted under drought and salt stress to investigate the interaction between root exudates and Nitraria tangutorum rhizosphere bacterial communities. We found that drought and salt stress increased rhizosphere soil pH (9.32 and 20.6%) and electrical conductivity (1.38 and 11 times), respectively, while decreased organic matter (27.48 and 31.38%), total carbon (34.55 and 29.95%), and total phosphorus (20 and 28.57%) content of N. tangutorum rhizosphere soil. Organic acids, growth hormones, and sugars were the main differential metabolites of N. tangutorum under drought and salt stress. Salt stress further changed the N. tangutorum rhizosphere soil bacterial community structure, markedly decreasing the relative abundance of Bacteroidota as r-strategist while increasing that of Alphaproteobacteria as k-strategists. The co-occurrence network analysis showed that drought and salt stress reduced the connectivity and complexity of the rhizosphere bacterial network. Soil physicochemical properties and root exudates in combination with salt stress affect bacterial strategies and interactions. Our study revealed the mechanism of plant–soil-microbial interactions under the influence of root exudates and provided new insights into the responses of bacterial communities to stressful environments.

Comparative metagenomic analysis reveals rhizosphere microbial community composition and functions help protect grapevines against salt stress

“…However, Menendez-Serra et al (2022) found that the microbial co-occurrence network was stable in ephemeral saline lakes under severe salinity fluctuations. Additionally, another study reported that the connectivity and complexity of the rhizosphere bacterial co-occurrence network were lowered in response to salt stress in Nitraria tangutorum ( Pan et al, 2022 ). The conflicting results suggest that besides salt, plant root exudates should not be ignored in the construction of co-occurrence networks.…”

“…The conflicting results suggest that besides salt, plant root exudates should not be ignored in the construction of co-occurrence networks. Pan et al (2022) reported that salt stress caused significant differences in the root exudates of N. tangutorum , especially organic acids, growth hormones, and sugars. In general, root exudate composition and quantity can change under abiotic stresses including drought ( Vives-Peris et al, 2018 ) and salinization ( Zhou et al, 2018 ).…”

Responses of Soil Microbial Survival Strategies and Functional Changes to Wet–Dry Cycle Events

“…Then, the "circlize" package in R software (4.1) was used to analyze the level of bacteria and fungi community. Gammaproteobacteria and Bacteroidota were defined as r-strategist bacteria, whereas Alphaproteobacteria and Acidobacteriota were defined as K-strategist bacteria according to the main idea of this study and previous studies [20,40]. The physicochemical properties and enzymatic activities of the 27 soil samples were analyzed using Spearman's correlation, and the Mantel test was used to describe the correlation [41].…”

“…To visualize the relationship between r/K-strategist bacteria and functional fungi more intuitively, we calculated the Spearman coefficients for the OTUs of r/K-strategist bacteria and fungi in the three sampling plots (|r| > 0.9, p < 0.001) and then established the co-occurrence network with established data (e.g., showing the number of nodes in Gammaproteobacteria, Bacteroidota, Alphaproteobacteria, Acidobacteriota, and fungi) [20]. We further identified environmental factors affecting soil microbial communities and composition through random forest analysis.…”

“…In addition, we were interested in the survival strategies of microorganisms during wet and dry events. Specifically, different microbial taxa exhibit different ecological characteristics [19,20]. For example, r-strategist bacteria are eutrophic microorganisms because of their high growth rate and low resource-use efficiency, and K-and r-strategist bacteria have opposite survival strategies, as K-strategist bacteria are oligotrophic microorganisms [21].…”