Biochar application alters soil metabolites and nitrogen cycle-related microorganisms in a soybean continuous cropping system

Biochar application is a promising practice to enhance soil fertility. However, it is unclear how field-aged biochar affects the soil metabolites and microbial communities in soybean fields. Here, the rhizosphere soil performance after amending with biochar addition rates at 0 (CK), 20 (B20), 40 (B40), and 60 t ha-1 (B60) was examined via a five-year in-situ field experiment based on a soybean continuous cropping system. Untargeted metabolomics and metagenomics analysis techniques were applied to study the regulatory mechanism of biochar on soybean growth from metabolomics and N cycle microbiology perspectives. We found that the contents of soil total N (TN), available N (Ava N), NH4+-N, and NO3--N were significantly increased with biochar addition amounts by 20.0-65.7 %, 3.6-10.7 %, 29.5-57.1 %, and 24.4-46.7 %, respectively. The B20, B40, and B60 triggered 259 (236 were up-regulated and 23 were down-regulated), 236 (220 were up-regulated and 16 were down-regulated), and 299 (264 were up-regulated and 35 were down-regulated) differential metabolites, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and topology analysis demonstrated that differential metabolites were highly enriched in seven metabolic pathways such as Oxidative phosphorylation and Benzoxazinoid biosynthesis. Moreover, ten differential metabolites were up-regulated in all three treatments with biochar. Biochar treatments decreased the Nitrospira abundance in soybean rhizosphere soil while increasing Bradyrhizobium abundance significantly in B60. Mantel test revealed that as the biochar addition rate grows, the correlation between Nitrospira and soil properties other than NO3--N became stronger. In conclusion, the co-application of biochar with fertilizers is a feasible and effective way to improve soil N supply, even though biochar has undergone field aging. This work offers new insights into the variations in soil metabolites and microbial communities associated with N metabolism processes under biochar addition in soybean continuous cropping soils.

Synergistic benefits of Funneliformis mosseae and Bacillus paramycoides: Enhancing soil health and soybean tolerance to root rot disease

To explore the response of soil metabolite composition to soybean disease, the effect of the combined inoculation of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria on soybean root rot caused by Fusarium oxysporum was studied. A factorial completely randomized design with three factors (AMF, Bacillus. paramycoides, and rot disease stress) was conducted, and eight treatments, including normal groups and stress groups, were performed using pot experiments. GC‒MS and enzymatic assays were used to evaluate the soil factors and soybean growth indicators. The results showed that there were significant differences in the composition of metabolites among the different treatment groups, and 23 metabolites were significantly related to soybean biomass. The combined inoculation of Funneliformis mosseae and Bacillus paramycoides resulted in a significant reduction in harmful soil metabolites associated with root rot disease, such as ethylbenzene and styrene. This reduction in metabolites contributed to improving soil health, as evidenced by enhanced soybean defence enzyme activities and microbial activity, and β-1,3-glucanase, chitinase and phenylalanine ammonia-lyase activities were improved to alleviate plant rhizosphere stress. Furthermore, soybean plants inoculated with the synergistic treatments exhibited reduced root rot disease severity and improved growth indicators compared to control plants. Plant height, root dry weight (RDW), and shoot and root fresh weight (SRFW) were improved by 4.18-53.79%, and the AM fungal colonization rate was also improved under stress. The synergistic application of Funneliformis mosseae and Bacillus paramycoides can effectively enhance soil health by inhibiting the production of harmful soil metabolites and improving soybean tolerance to root rot disease. This approach holds promise for the sustainable management of soil-borne diseases in soybean cultivation.

Enzymatic fermentation of rapeseed cake significantly improved the soil environment of tea rhizosphere

BACKGROUND

Rapeseed cake is an important agricultural waste. After enzymatic fermentation, rapeseed cake not only has specific microbial diversity but also contains a lot of fatty acids, organic acids, amino acids and their derivatives, which has potential value as a high-quality organic fertilizer. However, the effects of fermented rapeseed cake on tea rhizosphere microorganisms and soil metabolites have not been reported. In this study, we aimed to elucidate the effect of enzymatic rapeseed cake fertilizer on the soil of tea tree, and to reveal the correlation between rhizosphere soil microorganisms and nutrients/metabolites.

RESULTS

The results showed that: (1) The application of enzymatic rapeseed cake increased the contents of soil organic matter (OM), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), and available phosphorus (AP); increased the activities of soil urease (S-UE), soil catalase (S-CAT), soil acid phosphatase (S-ACP) and soil sucrase (S-SC); (2) The application of enzymatic rapeseed cake increased the relative abundance of beneficial rhizosphere microorganisms such as Chaetomium, Inocybe, Pseudoxanthomonas, Pseudomonas, Sphingomonas, and Stenotrophomonas; (3) The application of enzymatic rapeseed cake increased the contents of sugar, organic acid, and fatty acid in soil, and the key metabolic pathways were concentrated in sugar and fatty acid metabolisms; (4) The application of enzymatic rapeseed cake promoted the metabolism of sugar, organic acid, and fatty acid in soil by key rhizosphere microorganisms; enzymes and microorganisms jointly regulated the metabolic pathways of sugar and fatty acids in soil.

CONCLUSIONS

Enzymatic rapeseed cake fertilizer improved the nutrient status and microbial structure of tea rhizosphere soil, which was beneficial for enhancing soil productivity in tea plantations. These findings provide new insights into the use of enzymatic rapeseed cake as an efficient organic fertilizer and expand its potential for application in tea plantations.

Green manure increases peanut production by shaping the rhizosphere bacterial community and regulating soil metabolites under continuous peanut production systems

BACKGROUND

Green manure (GM) is a crop commonly grown during fallow periods, which has been applied in agriculture as a strategy to regulate nutrient cycling, improve organic matter, and enhance soil microbial biodiversity, but to date, few studies have examined the effects of GM treatments on rhizosphere soil bacterial community and soil metabolites from continuous cropping peanut field.

RESULTS

In this study, we found that the abundances of several functionally significant bacterial groups containing Actinobacteria, Acidobacteria, and genus Sphingomonas, which are associated with nitrogen cycling, were dramatically increased in GM-applied soils. Consistent with the bacterial community results, metabolomics analysis revealed a strong perturbation of nitrogen- or carbon-related metabolisms in GM-applied soils. The substantially up-regulated beneficial metabolites including sucrose, adenine, lysophosphatidylcholine (LPC), malic acid, and betaines in GM-applied soils may contribute to overcome continuous cropping obstacle. In contrast to peanut continuous cropping, planting winter wheat and oilseed rape in winter fallow period under continuous spring peanut production systems evidently improved the soil quality, concomitantly with raised peanut pod yield by 32.93% and 25.20%, in the 2020 season, respectively.

CONCLUSIONS

GMs application is an effective strategy to overcome continuous cropping obstacle under continuous peanut production systems by improving nutrient cycling, soil metabolites, and rhizobacterial properties.

Insights into the mechanism of the interference of sulfadiazine on soil microbial community and function

The accumulation of sulfonamides in the soil environment possessed the potential to change soil microbial community and function. Metabolomics is capable of providing insights into the carbon metabolic pool and molecular mechanisms associated with external stressors. Here we evaluated alternations in soil bacterial community and soil metabolites profiles under sulfadiazine (SDZ) exposure and proposed a potential mechanism that SDZ accumulation in soil affected soil organic matter (SOM) cycling. Sequencing analysis showed that the relative abundance of bacterial species associated with carbon cycling significantly decreased under high concentrations of SDZ exposure. Untargeted metabolomics analysis showed that 78 metabolites were significantly changed with the presence of SDZ in soil. The combination of functional predictions and pathway analysis both demonstrated that high concentrations of SDZ exposure could cause disturbance in anabolism and catabolism. Moreover, the noticeable decline in the relative content of carbohydrates under high concentrations of SDZ exposure might weaken physical separation and provide more chances for microbes to degrade SOM. The above results provided evidence that SDZ accumulation in soil held the potential to disturb SOM cycling. These findings spread our understanding about the environmental risk of antibiotic in the soil environment beyond the dissemination of antibiotic resistance.

Response of soil microbial communities to engineered nanomaterials in presence of maize (Zea mays L.) plants

With the intended application of engineered nanomaterials (ENMs) in agriculture, accurate assessment the effect of these ENMs on soil microbial communities is especially necessary. Here, maize plants were cultivated in soil amended by SiO₂, TiO₂, and Fe₃O₄ ENMs (100 mg kg^-1 soil) for four weeks. The impact of ENMs on bacterial community structure of the rhizosphere soil was investigated by using high-throughput sequencing. In addition, metabolites of maize rhizosphere soil were quantified by gas chromatography-mass spectrometry (GC-MS) based metabolomics. We found that the disturbance of ENMs on soil microbes are in the follow of Fe₃O₄>TiO₂>SiO₂. Exposure of Fe₃O₄ ENMs significantly reduced the abundance of nitrogen-fixation related bacteria Bradyrhizobiaceae (from 2.94% to 2.40%) and iron-redox bacteria Sediminibacterium (from 2.15% to 2.07%). Additionally, Fe₃O₄ ENMs significantly increased populations of Nocardioides (from 1.63% to 1.77%), Chitinophaga sancti (from 1.12% to 2.08%), Pantoea (from 1.31% to 2.22%), Rhizobiumand (from 1.41% to 1.74%) and Burkholderia-Paraburkholderia (from 1.50% to 2.09%), which are associated with carbon cycling and plant growth promoting. This study provides a perspective on the response of rhizosphere microbial community and low molecular weight metabolites to ENMs exposure, providing a comprehensive understanding of the environmental risk of ENMs.