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Background: Plant roots host a repertoire of bacteria and fungi, whose ecological interactions could improve their functions and plant performance. However, potential interactions and underlying mechanisms remain largely unknown in root-associated microbial communities at a continuous fine-scale. Results: We analyzed microbial intra- and inter-domain network topologies, keystone taxa, and interaction-related genes across four compartments (non-rhizosphere, rhizosphere, episphere and endosphere) from a soil-mangrove root continuum, using amplicon and metagenome sequencing technologies. We found that both intra- and inter-domain networks displayed notable differences in the structure and topology across four compartments. Compared to three peripheral compartments, the endosphere was a distinctive compartment with more intensive interactions in bacterial-fungal network than in bacterial or fungal network, which could be related to three bacterial keystone taxa (Vibrio, Anaerolineae and Desulfarculaceae) detected in the endosphere as they are known to intensify inter-domain interactions with fungi and stimulate biofilm formation. Also, high abundances of genes involved in cell-cell communications by quorum sensing (rhlI, lasI, pqsH and lasR) and aerobic cobamide biosynthesis (cobG, cobF and cobA) were detected in the endosphere.Conclusions: Our results reveal intensified inter-domain interactions of endophytes in the mangrove roots, creating a distinct micro-environment to promote a biofilm life-style.

Additional file 1. Supplementary materials of the full text, including of Table S1: The design of primers in six different amino acid sites; Figure S1: Thin-layer chromatography (TLC) to evaluate catalytic activities of the mutants for α-ketobutyric acid; Figure S2: SDS-PAGE to analyze the purified mutant protein. Figure S3: The concentration of L-2-Aminobutyric acid was detected by HPLC; Figure S4: Chiral analysis of aminobutyric acid; Figure S5: Enzyme kinetic curve of ω-transaminase.

Additional file 1:. The detailed method for measuring nitrogen fixation rate by acetylene reduction assay.

Additional file 2. Raw materials of the full text, containing the original, unprocessed and uncropped version of the table 1, Fig 2 and Fig 5 in manuscript. The schematic view of the pET28 plasmid as well as the designed gene structure in assay.

Additional file 2: Table S1. A summary of reads information and microbial classification at different taxonomical levels. Table S2. Pearson’s correlations between the abundance of diazotrophic genera and the nitrogen fixation rate (NFR). Table S3. Relative abundances of diazotrophic communities at the genus level. Table S4. Mantel test for the correlations between diazotrophic community structure and sediment properties. Fig. S1. The location of the sampling habitats at the Qi’ao Island, Guangdong Province, China. Fig. S2. Relationships between the depth of mangrove sediments and the NFR (a), water content (b), salinity (c), Shannon index (d) and Chao1 index (e). NFR was represented as acetylene reduction (nmol g-1 h-1) in this research. Black lines and grey shaded areas represent linear regressions and 95% confidence intervals, respectively. R2 was obtained by linear regression analysis and p was obtained by Pearson’s correlation analysis. Fig. S3. The in-depth profile of physicochemical properties. The concentration of NH4+ (a), NO2- (b), NO3- (c), pH (d), water content (e), salinity (f), total Fe (g), available Fe (h) and Fe3+ (i) across 10 depths of mangrove sediments. Boxplots depict the 25-75% quantile range of the selected measurements, with the centerline depicting the median (50% quantile). Whiskers show the minimum and maximum values. Fig. S4. Bray-Curtis distance-based hierarchical clustering of diazotrophic communities across 10 depths of mangrove sediments. The color gradient represents sediment depth.

Long-term shallow rotary tillage has reduced the soil quality and restricted the crop yield growth of farmland in Southern China. Deep tillage can effectively loosen the soil and reduce the compaction of deep soil, while no-tillage can ensure the sustainable use of soil. In this study, we selected three paddy-upland multiple cropping rotation areas in Southern China. Two tillage regimes were carried out, one (DT) where rice straw mulching was followed by deep tillage (subsoiling 30 cm) and then, for the next three years, no-tillage in the flue-cured tobacco planting season and rotary tillage in the rice planting season vs a control (RT) where no tillage after rice straw mulching was carried out, and rotary tillage was conducted in both the flue-cured tobacco planting season and rice planting season for the next three years. We compared the yield and output value of flue-cured tobacco and grain yield under DT and RT tillage regimes in the three areas, and analyzed the economic benefits brought by DT. Furthermore, we identified the effects of DT on soil aggregates, soil organic carbon (SOC), crop growth, and nutrient uptake at the experimental site in Yunyuan. Compared with RT, DT can increase the weight proportion of macroaggregates and SOC content in the 10–30 cm soil layer and improve the stability of soil aggregates in the 0–30 cm soil layer. In 2019, the mean weight diameter (MWD) and geometric mean diameter (GMD) of the 0–30 cm soil layer increased by 0.47 mm and 0.20 mm, respectively, on average. In 2020, the MWD and GMD increased by 0.33 mm and 0.11 mm, respectively, on average. DT promoted the roots of flue-cured tobacco to extend down to the 30–40 cm soil layer, and DT flue-cured tobacco plants had more leaves, higher dry matter weight, and greater N and P absorption than RT flue-cured tobacco. These results were conducive to the increase of yield and output value of flue-cured tobacco. During the three-year test period, the yield of flue-cured tobacco increased by 4%–9%, the output value increased by 7%–13%, and the net economic benefits also increased. In the paddy-upland multiple cropping rotation areas of Southern China, DT is more conducive to the improvement of dryland crop yield than paddy field crop yield. Intermittent deep tillage (one-time deep tillage and then no tillage) is expected to provide a potential way to effectively increase production, high economic efficiency, and soil improvement in promoting sustainable agricultural development and cleaner production.

Endophytic bacteria are generally helpful for plant growth and protection. We isolated from tobacco seeds three Pseudomonas strains (K03, Y04, and N05) that could produce siderophores, indole-3-acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase, fix nitrogen, dissolve phosphorus and potassium, and tolerate heavy metals. In pot experiments, the three isolated strains significantly promoted root growth and increased the root enzyme activity in Nicotiana tobacum K326. Furthermore, bacterial inoculations increased the proportion of residual lead (Pb) by 8.36%–51.63% and decreased the total Pb content by 3.28%–6.38% in the contaminated soil during tobacco planting, compared with uninoculated soils. An effective decrease in Pb content was also found in tobacco leaves with bacterial inoculations. K03 inoculation decreased the Pb content in the upper leaves by 49.80%, and Y04 inoculation had the best effect, decreasing the Pb content in the middle leaves by 70.12%. Additionally, soil pH and root activity had significant effects on transformation and translocation of Pb. The study suggested that in response to Pb pollution in soil, a reasonable application of endophytes (e.g., Pseudomonas) might be a promising approach in promoting tobacco growth and reducing Pb content in tobacco, while simultaneously enhancing Pb stabilization in soils.

Cet article analyse l'expansion rapide entre 1998 et 2002 de l'enseignement superieur en Chine, qui a su faire evoluer ses universites d'un statut elitiste a une democratisation de leur acces. En contrepartie, les consequences de cette hausse exponentielle des effectifs sont inquietantes au niveau budgetaire et egalement au niveau de la qualite de l'enseignement.