With the warming global climate, drought stress is considered to be the most important abiotic factor limiting plant growth and yield in the world. Drought stress has serious impacts on crop production. Many researchers have studied the influences of drought stress on crop production and plant physiology; however, few researchers have combined root exudates with root-associated microbiomes for their mutual effects under drought conditions. In this review, we systematically illustrate the impact of drought stress on root exudates and root-associated microbiomes, and then we discuss the mutual regulation of root-associated microbiomes and the host plant in helping the plant adapt to drought. Finally, we construct a framework for the mutual connections between the plant, root exudates, and the microbiome. We hope this review can provide some significant guidelines to promote the study of drought resistance in plants in association with the rhizosphere microbiota.

The farmland residual film pollution caused by traditional PE film has an adverse impact on crops and the environment. Polypropylene carbonate (PPC) film is a fully biodegradable film that can alleviate “white pollution”. In this study, the soil physicochemical properties and the composition and function of the soil community of FM (PPC film mulching) and CK (no film) treatments were determined to explore the effect of PPC film mulching on soil and the soil microbial community. Furthermore, the microorganisms at different time periods during the degradation of PPC mulch film were also analyzed. The results showed that film mulching increased soil pH but decreased the contents of EC and SOC, and there was no significant difference in the contents of AP and AK. The relative abundance of the phyla Acidobacteria was increased with film mulching, and the relative abundance of the genera MB_A2_108 also increased in the film mulched soil. Among the soil physicochemical properties, pH and SOC were the most important factors leading to changes in the composition of the bacterial and fungal communities. PPC film mulching had no significant effect on soil microbial community abundance and diversity. In addition, Pseudomonas, Flavobacterium, and Rhizobacter were dominant in the degradation of PPC film. Our research results provide a scientific theoretical basis for soil safety and the large-scale use of PPC biodegradable mulching films and a research foundation for the degradation of PPC plastics.

The barriers caused by continuous tillage have had a negative impact on the crop and soil environment. Black soils are economically important as a valuable natural resource in Northeast China, but limited soil resources have led to continuous planting of major food crops and medicinal plants. At present, the extent to which two different types of plants—grains and medicinal plants that are successively grown on the same soil—have an impact on soil quality and microbiology is not known. In this study, we investigated the effects of different types of long-term continuous cropping on soil and soil microbial communities by determining the physicochemical properties, the soil community composition and function of grain crops and medicinal-plant soils with more than five years of continuous cropping, as well as fallow soils. The results showed that long-term continuous cropping reduced the pH of different types of soils, but there was no significant difference in the content of AK. The relative abundance of beneficial dominant phyla, such as Actinomycetes, Acidobacteria, and Green Campylobacter decreased and the relative abundance of pathogenic genera such as Alternaria and Didymellaceae, increased after the long-term continuous cropping of DM (grain crops) and DG (medicinal plants). Specifically, continuous cropping increased the relative abundance of fungi with pathogenic potential, such as Sordariomycetes, Dothideomycetes, Saccharomycetes, and Mucoromycetes in grain soils and Agaricostilbomycetes in herb soils. Among the soil physicochemical properties, NH₄⁺-N and pH were the most important factors contributing to changes in the composition of bacterial and fungal communities, respectively. Continuous cropping of different types of plants altered the diversity of the microbial communities, with the most significant effect from the continuous cropping of food crops. Our findings provide a scientific and theoretical basis for future agricultural research to improve soil microbial activity, mitigate continuous-cropping barriers, and increase productivity.

The effects of global warming, population growth, and economic development are increasing the frequency of extreme weather events, such as drought. Among abiotic stresses, drought has the greatest impact on soil biological activity and crop yields. The rhizosphere microbiota, which represents a second gene pool for plants, may help alleviate the effects of drought on crops. In order to investigate the structure and diversity of the bacterial communities on drought stress, this study analyzed the differences in the bacterial communities by high-throughput sequencing and bioinformatical analyses in the rhizosphere of Arabidopsis thaliana under normal and drought conditions. Based on analysis of α and β diversity, the results showed that drought stress had no significant effect on species diversity between groups, but affected species composition. Difference analysis of the treatments showed that the bacteria with positive responses to drought stress were Burkholderia-Caballeronia-Paraburkholderia (BCP) and Streptomyces. Drought stress reduced the complexity of the rhizosphere bacterial co-occurrence network. Streptomyces was at the core of the network in both the control and drought treatments, whereas the enrichment of BCP under drought conditions was likely due to a decrease in competitors. Functional prediction showed that the core bacteria metabolized a wide range of carbohydrates, such as pentose, glycans, and aromatic compounds. Our results provide a scientific and theoretical basis for the use of rhizosphere microbial communities to alleviate plant drought stress and the further exploration of rhizosphere microbial interactions under drought stress.

With the development of microbial fertilizers, efforts have been made to enrich the strain resources of plant growth-promoting rhizobacteria (PGPR) in maize and to compare the growth-promoting effects of synthetic microbial communities (SynComs) with those of single strains. To achieve this, phenotypic measurements and RNA sequencing (RNA-seq) were performed on maize roots treated with SynComs and single-strain bacterial suspensions, aiming to investigate the regulatory influence of PGPR on differential gene expression and key metabolic pathways in maize roots. In this study, 59 PGPR strains were selected, representing genera including Bacillus, Pseudomonas, Burkholderia sp., Curtobacterium pusillum, Acidovorax, Sphingobium, Mitsuaria, Bacterium, Rhodanobacter, Variovorax, Ralstonia, Brevibacillus, Terrabacter, Flavobacterium, Comamonadaceae, Achromobacter, Paraburkholderia, and Massilia. Based on the growth-promoting effects observed in pot experiments, optimal bacterial strains were selected according to the principles of functional complementarity and functional superposition to construct the SynCom. The selected strains included Burkholderia sp. A2, Pseudomonas sp. C9, Curtobacterium pusillum E2, and Bacillus velezensis F3. The results demonstrated that individual strains exerted measurable growth-promoting effects on seedlings; however, the growth-promoting capability of the SynCom was significantly stronger than that of single strains. The synthetic microbial community ALL group markedly increased root length, shoot fresh weight, shoot dry weight, number of branches, and number of root tips in maize seedlings. RNA-seq analysis of maize roots treated with the SynCom (ALL group) was conducted in comparison with CK, A2, C9, E2, and F3 treatment groups. A total of 5245 differentially expressed genes (DEGs) were identified, of which only 133 were common across treatments. GO and KEGG analyses revealed that DEGs were enriched in multiple biological processes, including cellular amide biosynthetic and metabolic processes, flavonoid biosynthetic and metabolic processes, carbohydrate metabolism, amino acid metabolism, lipid metabolism, and translation. The majority of enriched pathways were associated with primary and secondary metabolism, indicating that these bacterial strains promote plant growth by modulating a wide range of metabolic pathways in plant cells. Overall, this study provides a molecular framework for understanding the mechanisms underlying the growth-promoting effects of SynComs on maize roots and offers valuable insights for future research aimed at identifying key regulatory genes.

Crop diversification is pivotal in sustainable agriculture, influencing soil microbial communities and soil nutrient cycling functions. Yet, the impacts of incorporating medicinal plants into crop diversification strategies on the functional characteristics of these microbial communities remain understudied. This research elucidates the benefits of diversified cropping systems by assessing soil nutrient content, diversity and composition of soil microorganisms, the abundance of functional genes involved in carbon (C), nitrogen (N) and phosphorus (P) cycling, and overall agricultural productivity; collectively referred to as ecological benefits. The experimental design included four treatment groups: (1) continuous maize (Zea mays L.) cultivation (MC); (2) maize–A. lancea (Atractylodes lancea Thunb.) intercropping (MA); (3) maize–sorghum (Sorghum bicolor L.) rotation (MS); and (4) maize–A. lancea intercropping combined with sorghum rotation (MSA). Findings indicate that diversified cropping treatments significantly enhance the alpha diversity of soil bacterial communities over fungal communities. NH₄⁺ and NO₃⁻ predominantly influence the composition of soil bacterial communities, with a notable increase in the relative abundance of Acidobacteriota, Gemmatimonadota, and Chloroflexi. Compared to MC treatment, the MA and MSA treatments significantly increased the abundance of C (121.44%, 294.26%), N (206.57%, 294.26%), and P (112.02%, 225.84%) cycling genes. The inverse variance weighting evaluation demonstrates that, compared to the MC treatment, the MS (5.34) and MSA (8.15) treatments significantly boost soil ecological benefits. Overall, diversifying the cultivation of A. lancea with grains can enhance the ecological benefits of the soil. This study offers new perspectives on diversified planting, particularly in terms of species selection and practical combinations on farmland.