Effect of microbial transformation induced by metallic compound additives and temperature variations during composting on suppression of soil-borne pathogens.

Agricultural wastes can be modified by composting and reused in soil to suppress soil-borne pathogens, which was proved to be closely related with microbial parameters. However, the microbial community in compost can be directly altered by temperature variations and metallic compound additives during composting process. The present study collected samples in various stages of the 35-day composting process, in which a study control (no additives) and different metallic compound additives, including magnesium oxide (MgO), alum (AlK(SO4)3), calcium oxide (CaO) and ferrous sulfate (FeSO4), were set in the bespoke compost with cow dung and corn stalk. The results showed that the additives prolonged the composting maturity process, whereas no consistent influence on the temperature variation and microbial community was observed. Temperature variations during composting significantly varied the bacteria and fungi diversity and community, especially the bacteria phyla of Firmicutes and Proteobacteria, while the bacteria were shown similar in Day 14 and Day 35 by PCA analysis. Meanwhile the samples from Day 14 and Day 35 showed stable suppressive effects on R. solani. and F. oxysporum, especially in D14 shown as 73.12%-88.16% and 30.95-58.55%, respectively, which were significantly related with the phyla of Firmicutes and Proteobacteria. In conclusion, temperature variations during composting process had a more significant impact than metallic compound additives on the microbial community and diversity, which resulted in significantly influence on the pathogen suppression. Suitable composting duration could produce effective suppressive products on soil-borne pathogens, for which further study was needed.

Treatment With Wheat Root Exudates and Soil Microorganisms From Wheat/Watermelon Companion Cropping Can Induce Watermelon Disease Resistance Against Fusarium oxysporum f. sp. niveum.

Companion cropping with wheat (Triticum aestivum L.) can enhance watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] wilt disease resistance against Fusarium oxysporum f. sp. niveum. However, the mechanism of resistance induction remains unknown. In this study, the effects of microbial community dynamics and the interactions between wheat and watermelon plants, particularly the effect of wheat root exudates on watermelon resistance against F. oxysporum f. sp. niveum, were examined using a plant-soil feedback trial and plant tissue culture approach. The plant-soil feedback trial showed that treating watermelon with soil from wheat/watermelon companion cropping decreased watermelon wilt disease incidence and severity, increased lignin biosynthesis- and defense-related gene expression, and increased ß-1,3-glucanase activity in watermelon roots. Furthermore, soil microbes can contribute to increasing disease resistance in watermelon plants. Tissue culture experiments showed that both exogenous addition of wheat root exudates and companion cropping with wheat increased host defense gene expression, lignin and total phenols, and increased ß-1,3-glucanase activity in watermelon roots. In conclusion, both root exudates from wheat and the related soil microorganisms in a wheat/watermelon companion cropping system played critical roles in enhancing resistance to watermelon wilt disease induced by F. oxysporum f. sp. niveum.

Soil organic carbon stability mediate soil phosphorus in greenhouse vegetable soil by shifting phoD-harboring bacterial communities and keystone taxa.

Addition of organic amendments, such as manure and straw, to arable fields as a partial substitute for mineral phosphorus (P), are a sustainable practice in high-efficiency agricultural production. Different organic inputs may induce varied soil organic carbon (OC) stability and phoD harboring microbes, subsequently regulate P behavior, but the underlying mechanisms are poorly understood. A 11-year field experiment examined P forms by 31P-nuclear magnetic resonance (NMR), OC chemical composition by 13C NMR, and biologically-based P availability methods, phoD bacterial communities, and their co-occurrence in soils amended with chemical P fertilizer (CF), chemical P partly substituted by organic amendments including pig manure (CM), a mixture of pig manure and corn straw (CMS), and corn straw (CS), with equal P input in all treatments. Organic amendments significantly increased soil labile Pi (CaCl2-P, citrate-P, 2.91-3.26 and 1.16-1.32 times higher than CF) and Po (enzyme-P, diesters, 4.08-7.47 and 1.71-2.14 times higher than CF) contents and phosphatase activities, while significantly decreased aromaticity (AI) and recalcitrance indexes (RI) of soil C, compared with CF. The keystone genera in manured soils (Alienimomas and Streptomyces) and straw-applied soils (Janthinobacterium and Caulobacter) were significantly correlated with soil enzyme-P, microbial biomass P (MBP), diesters, and citrate-P. Soil AI and RI were significantly correlated with the phoD keystone and soil P species. It suggested that the keystone was impacted by soil OC stability and play a role in regulating P redistribution in amended soils. This study highlights how manure and straw incorporation altered soil OC stability, shaped the phoD harboring community, and enhanced soil P biological processes promoted by the keystone taxa. The partial substitution of mineral P by mixture of manure and straw is effectively promote soil P availability and beneficial for environmental sustainability.

The role of the biogas slurry microbial communities in suppressing fusarium wilt of cucumber.

The clarification of the suppressive effect of biogas slurries (BSs) on soil-borne plant pathogens is needed for their large-scale use as a biocontrol tool in potting soil in order to understand the mechanisms of suppression. In this study, pig manure biogas slurry (PS) and vinasse biogas slurry (VS) were used to conduct assays of pathogen mycelial growth suppression and pot experiment to evaluate their effects on the growth of Fusarium. oxysporum f. sp. cucumerinum (FOC) mycelia and cucumber fusarium wilt. The microbial communities of the PS and VS were deeply analyzed to explore the key taxa and potential mechanisms. Results showed that the PS and VS have similar suppression on FOC mycelia and on the control efficiency, while they were significantly weakened when the PS and VS were used after sterilization. The microbial parameters of the two BSs were obviously different, and functional microbial taxa for disease resistance were observed in the two BSs. Spearman correlation showed that genera of the Pseudomonas, Ochrobactrum, Papiliotrema, etc., were the suppression-related taxa in the PS, while Leucobacter, unclassified_Microbacteriaceae, etc. in the VS. Overall, various key taxa in the PS and VS produced similar suppression on cucumber fusarium wilt.

Intercropping with Potato-Onion Enhanced the Soil Microbial Diversity of Tomato.

Intercropping can achieve sustainable agricultural development by increasing plant diversity. In this study, we investigated the effects of tomato monoculture and tomato/potato-onion intercropping systems on tomato seedling growth and changes of soil microbial communities in greenhouse conditions. Results showed that the intercropping with potato-onion increased tomato seedling biomass. Compared with monoculture system, the alpha diversity of soil bacterial and fungal communities, beta diversity and abundance of bacterial community were increased in the intercropping system. Nevertheless, the beta-diversity and abundance of fungal community had no difference between the intercropping and monoculture systems. The relative abundances of some taxa (i.e., Acidobacteria-Subgroup-6, Arthrobacter, Bacillus, Pseudomonas) and several OTUs with the potential to promote plant growth were increased, while the relative abundances of some potential plant pathogens (i.e., Cladosporium) were decreased in the intercropping system. Redundancy analysis indicated that bacterial community structure was significantly influenced by soil organic carbon and pH, the fungal community structure was related to changes in soil organic carbon and available phosphorus. Overall, our results suggested that the tomato/potato-onion intercropping system altered soil microbial communities and improved the soil environment, which may be the main factor in promoting tomato growth.

Gene Expression and K+ Uptake of Two Tomato Cultivars in Response to Sub-Optimal Temperature.

Sub-optimal temperatures can adversely affect tomato (Solanum lycopersicum) growth, and K+ plays an important role in the cold tolerance of plants. However, gene expression and K+ uptake in tomato in response to sub-optimal temperatures are still not very clear. To address these questions, one cold-tolerant tomato cultivar, Dongnong 722 (T722), and one cold-sensitive cultivar, Dongnong 708 (S708), were exposed to sub-optimal (15/10 °C) and normal temperatures (25/18 °C), and the differences in growth, K+ uptake characteristics and global gene expressions were investigated. The results showed that compared to S708, T722 exhibited lower reduction in plant growth rate, the whole plant K+ amount and K+ net uptake rate, and T722 also had higher peroxidase activity and lower K+ efflux rate under sub-optimal temperature conditions. RNA-seq analysis showed that a total of 1476 and 2188 differentially expressed genes (DEGs) responding to sub-optimal temperature were identified in S708 and T722 roots, respectively. Functional classification revealed that most DEGs were involved in "plant hormone signal transduction", "phenylpropanoid biosynthesis", "sulfur metabolism" and "cytochrome P450". The genes that were significantly up-regulated only in T722 were involved in the "phenylpropanoid biosynthesis" and "plant hormone signal transduction" pathways. Moreover, we also found that sub-optimal temperature inhibited the expression of gene coding for K+ transporter SIHAK5 in both cultivars, but decreased the expression of gene coding for K+ channel AKT1 only in S708. Overall, our results revealed the cold response genes in tomato roots, and provided a foundation for further investigation of mechanism involved in K+ uptake in tomato under sub-optimal temperatures.