Acidification induce chemical and microbial variation in tea plantation soils and bacterial degradation of the key acidifying phenolic acids.

Camellia sinensis is an important economic plant grown in southern subtropical hilly areas, especially in China, mainly for the production of tea. Soil acidification is a significant cause of the reduction of yield and quality and continuous cropping obstacles in tea plants. Therefore, chemical and microbial properties of tea growing soils were investigated and phenolic acid-degrading bacteria were isolated from a tea plantation. Chemical and ICP-AES investigations showed that the soils tested were acidic, with pH values of 4.05-5.08, and the pH negatively correlated with K (p < 0.01), Al (p < 0.05), Fe and P. Aluminum was the highest (47-584 mg/kg) nonessential element. Based on high-throughput sequencing, a total of 34 phyla and 583 genera were identified in tea plantation soils. Proteobacteria and Acidobacteria were the main dominant phyla and the highest abundance of Acidobacteria was found in three soils, with nearly 22% for the genus Gp2. Based on the functional abundance values, general function predicts the highest abundance, while the abundance of amino acids and carbon transport and metabolism were higher in soils with pH less than 5. According to Biolog Eco Plate™ assay, the soil microorganisms utilized amino acids well, followed by polymers and phenolic acids. Three strains with good phenolic acid degradation rates were obtained, and they were identified as Bacillus thuringiensis B1, Bacillus amyloliquefaciens B2 and Bacillus subtilis B3, respectively. The three strains significantly relieved the inhibition of peanut germination and growth by ferulic acid, p-coumaric acid, p-hydroxybenzoic acid, cinnamic acid, and mixed acids. Combination of the three isolates showed reduced relief of the four phenolic acids due to the antagonist of B2 against B1 and B3. The three phenolic acid degradation strains isolated from acidic soils display potential in improving the acidification and imbalance in soils of C. sinensis.

Potential Role of Sugars in the Hyphosphere of Arbuscular Mycorrhizal Fungi to Enhance Organic Phosphorus Mobilization.

Arbuscular mycorrhizal (AM) fungi engage in symbiosis with more than 80% of terrestrial plants, enlarging root phosphorus (P) absorption volume by producing extensive extraradical hyphae (ERH) in the soil. In addition, AM fungi recruit and cooperate with soil bacteria to enhance soil organic P mobilization and improve fungal and plant fitness through hyphal exudates. However, the role of the dominant compounds in the hyphal exudates in enhancing organic P mobilization in the mycorrhizal pathway is still not well understood. In this study, we added sugars, i.e., glucose, fructose, and trehalose, which are detected in the hyphal exudates, to the hyphal compartments (HCs) that allowed the ERH of the AM fungus to grow or not. The results showed that in AM fungus-inoculated pots, adding three sugars at a concentration of 2 mmol C kg-1 soil significantly increased the phosphatase activity and facilitated the mobilization of organic P in the HCs. The addition of fructose at a concentration of 2 mmol C kg-1 soil was the most efficient in increasing the phosphatase activity and enhancing organic P mobilization. The released inorganic P was then absorbed by the ERH of the AM fungus. The enhanced mobilization of organic P was correlated with the increase in phoD gene number and the changing bacterial community in the presence of fungal hyphae. The sugar addition enriched the relative abundance of some bacterial taxa, e.g., Betaproteobacteriales. Our study suggested that the addition of the sugars by mycorrhizae could be a pivotal strategy in managing P uptake in agricultural production, potentially directing future practices to optimize plant-fungi-bacteria interactions for improved P use efficiency.

Arbuscular mycorrhizal fungi enhance plant phosphorus uptake through stimulating hyphosphere soil microbiome functional profiles for phosphorus turnover.

The extraradical hyphae of arbuscular mycorrhizal (AM) fungi are colonized by different bacteria in natural and agricultural systems, but the mechanisms by which AM fungi interact with the hyphosphere soil microbiome and influence soil organic phosphorus (P) mobilization remain unclear. We grew Medicago in two-compartment microcosms, inoculated with Rhizophagus irregularis, or not, in the root compartment and set up P treatments (without P, with P addition as KH2 PO4 or nonsoluble phytate) in the hyphal compartment. We studied the processes of soil P turnover and characterized the microbiome functional profiles for P turnover in the hyphosphere soil by metagenomic sequencing. Compared with the bulk soil, the hyphosphere soil of R. irregularis was inhabited by a specific bacterial community and their functional profiles for P turnover was stimulated. At the species level, the shift in hyphosphere soil microbiome was characterized by the recruitment of the genome bin2.39 harbouring both gcd and phoD genes and genome bin2.97 harbouring the phoD gene, which synergistically drove nonsoluble phytate mobilization in the hyphosphere soil. Our results suggest that AM fungi recruits a specific hyphosphere soil microbiome and stimulated their functional profiles for P turnover to enhance utilization of phytate.

Controlled-Release Diammonium Phosphate Alleviates Apple Replant Disease: An Integrated Analysis of Soil Properties, Plant Growth, and the Soil Microbiome.

Exogenous application of nitrogen (N) and phosphate (P) has been demonstrated to alleviate apple replant disease (ARD). Yet, the effect of controlled-release diammonium phosphate (C-DAP), which continuously supply N and P for ARD control, is still poorly understood. Applying C-DAP markedly alleviated the typical symptoms of ARD. C-DAP maintained soil N and P at relatively high and stable levels during the entire growth period of the replanted seedlings, thus, limiting the copy number of the four key pathogenic Fusarium species that cause ARD. Particularly, continuously supplying N and P by C-DAP established a higher fungal diversity than that of conventional diammonium phosphate and induced the fungal community to be more similar to fumigated soil. The positive effect of C-DAP originated from the synergistic effects of regulating microorganisms and enhancing the resistance of the plant caused by a continuous nutrient supply. These findings provide a new perspective in the management of soil-borne diseases.

Comprehensive Analysis of the Influence of Fulvic Acid from Paper Mill Effluent on Soil Properties, Soil Microbiome, and Growth of Malus hupehensis Rehd. Seedlings under Replant Conditions.

In this study, the potential regulatory effects of fulvic acid extracted from paper mill effluent (PFA) in apple replant disease (ARD) were investigated through a comprehensive experimental evaluation of the effects of PFA on soil properties, growth inhibition of apple replant pathogens, and growth of replanted Malus hupehensis Rehd. seedlings. PFA with a relatively lower molecular weight was mainly composed of carbohydrates, lignin derivatives, and polysaccharides and was rich in functional groups such as carboxyl and phenolic hydroxyl groups. Treatment with PFA dosages ranging from 2 to 3 g/pot significantly increased available phosphorus (P) in soil by 47.5 to 57.5% when compared with the control without PFA, indicating that PFA had a positive effect in activating P. In addition, PFA stimulated the growth of replanted seedlings by promoting root elongation, enhancing leaf photosynthesis, and increasing the activity of root antioxidant enzymes including superoxide dismutase, peroxidase, and catalase. However, no convincing evidence was found that application of different dosages of PFA had remarkable effects on soil pH, inorganic nitrogen, available potassium, organic matter, and the numbers of bacteria and fungi. Notably, PFA had no effect on the copy number of the main pathogenic fungi causing ARD, including Fusarium oxysporum, Fusarium solani, Fusarium proliferatum, and Fusarium moniliforme. Overall, PFA can alleviate ARD to a certain extent mainly through its effects on improving the resilience of replanted young seedlings rather than by affecting soil microorganisms or providing nutrients.

Foetidibacter luteolus gen. nov., sp. nov., isolated from the rhizosphere of Salvia miltiorrhiza.

A polyphosphate-producing bacterium, YG09T, was isolated from the rhizosphere of Salvia miltiorrhiza. Its colonies were 2.0-3.0 mm in diameter, smooth, circular, convex and yellow after growth on R2A at 28 °C for 72 h, with aerobic, Gram-stain-negative, non-motile and rod-shaped bacteria. The strain was found to grow at 10-40 °C (optimum 37 °C), pH 5.5-8.0 (optimum 6.0), with 0-0.6% (w/v) NaCl (optimum 0). Chemotaxonomic analysis showed menaquinone-7 as the only quinone present; C15: 1 iso G, C15: 1 iso, C16: 0, C16: 0 3OH, C17: 0 iso 3OH, summed feature 3 (C16:1 ω7c and/or C16:1 ω6c) as the major fatty acids (> 5%), and phosphatidylethanolamine, three unidentified phospholipids, four unidentified polar lipids, three unidentified aminolipids, and one unidentified amino phospholipid as the polar lipids. The DNA G + C content was 44.6 mol%. The 16S rRNA gene sequences of the isolate showed highest similarities to Panacibacter ginsenosidivorans Gsoil 1550T (93.6%), Filimonas endophytica SR2-06T (93.4%), Parasegetibacter terrae SGM2-10T (92.8%), and Arvibacter flaviflagrans C-1-16T (92.7%), within the family Chitinophagaceae of the phylum Bacteroidetes. The ANI values between strain YG09T and Panacibacter ginsenosidivoran Gsoil 1550T, Filimonas endophytica SR2-06T and Filimonas lacunae YT21T were 69.4, 68.3 and 68.7%, respectively. Based on phenotypic, genotypic and phylogenetic analyses, strain YG09T represents a novel genus in the family Chitinophagaceae, for which the name Foetidibacter luteolus gen. sp. nov. is proposed. The type strain is Foetidibacter luteolus YG09T (= MCCC 1K04042T = KCTC 72595T).