Microbial community responses to multiple soil disinfestation change drivers

Rhizosphere microbial community assembly as influenced by reductive soil disinfestation to resist successive cropping obstacle

BACKGROUND

Reductive soil disinfestation (RSD), which involves creating anaerobic conditions and incorporating large amounts of organic materials into the soil, has been identified as a reliable strategy for reducing soilborne diseases in successive cropping systems. However, limited research exists on the connections between soil microorganism composition and plant diseases under various types of organic material applications. This study aimed to evaluate the effects of distinct RSD strategies (control without soil amendment; RSD with 1500 kg ha-1 molasses powder; RSD with 3000 kg ha-1 molasses powder; RSD with 3000 kg ha-1 molasses powder and 37.5-41.3 kg ha-1 microbial agent) on the plant disease index, bacterial community composition and network structure in rhizosphere soil.

RESULTS

RSD treatments significantly reduced the occurrence of black shank disease in tobacco and increased soil bacterial diversity. High amounts of molasses powder in RSD treatments further enhanced disease inhibition and reduced fungal abundance and Shannon index. RSD also increased the relative abundance of bacterial phylum Firmicutes and fungal phylum Ascomycota, while decreasing the relative abundance of bacterial phyla Chloroflexi and Acidobacteriota and fungal phylum Basidiomycota in rhizosphere soil. A multiple regression model identified bacterial positive cohesion as the primary factor influencing the plant disease index, with a greater impact than bacterial negative cohesion and community stability. The competition among beneficial bacteria for creating a healthy rhizosphere environment is likely a key factor in the success of RSD in reducing plant disease risk.

CONCLUSION

RSD, especially with higher rates of molasses powder, is a viable strategy for controlling black shank disease in tobacco and promoting soil health by fostering beneficial microbial communities. This study provides guidelines for soil management and plant disease prevention. © 2024 Society of Chemical Industry.

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.

Effect of continuous planting on Casuarina equisetifolia rhizosphere soil physicochemical indexes, microbial functional diversity and metabolites

Continuous planting has a severe impact on the growth of Casuarina equisetifolia. In this study, the effects of three different long-term monocultures (one, two and three replanting) on the physicochemical indexes, microbial functional diversity, and soil metabolomics were analyzed in C. equisetifolia rhizosphere soil. The results showed that rhizosphere soil organic matter content, cation exchange capacity, total and available nitrogen, total and available phosphorus, and total and available potassium contents significantly decreased with the increasing number of continuous plantings. The evaluation of microbial functional diversity revealed a reduction in the number of soil microorganisms that rely on carbohydrates for carbon sources and an increase in soil microorganisms that used phenolic acid, carboxylic acid, fatty acid, and amines as carbon sources. Soil metabolomics analysis showed a significant decrease in soil carbohydrate content and a significant accumulation of autotoxic acid, amine, and lipid in the C. equisetifolia rhizosphere soil. Consequently, the growth of C. equisetifolia could hinder total nutrient content and their availability. Thus, valuable insights for managing the cultivation of C. equisetifolia and soil remediation were provided.

Facilitating effects of the reductive soil disinfestation process combined with Paenibacillus sp. amendment on soil health and physiological properties of Momordica charantia

Reductive soil disinfestation (RSD) is an anaerobic and facultative anaerobic microbial-mediated soil management process. The extent of improvement of diseased soil properties by RSD relative to comparable healthy soil is, however, not well characterized. Importantly, how to promote the colonization efficiency of these facultative anaerobic functional species to ensure soil and plant health remain unknown. Here, Fusarium wilt-diseased soil of Momordica charantia grown under a plastic-shed field (PS-CK) was used to conduct molasses-RSD (MO-RSD) along with Paenibacillus sp. (a model of facultative anaerobic species) (MO_PA-RSD) treatment, and the soil from a nearby open-air paddy field was considered comparable healthy soil (OA-CK). Both RSD treatments significantly improved the properties of PS-CK soil, and the extent of improvement of soil pH, Fusarium oxysporum reduction efficiency (98.36%~99.56%), and microbial community and functional composition were higher than that achieved for OA-CK soil, which indicated that RSD-regulated most soil properties outperformed those of the comparable healthy soil. The disease incidence and ascorbic acid content of M. charantia in MO-RSD- and MO_PA-RSD-treated soils were considerably decreased, while the weight and soluble protein contents were correspondingly increased, as compared to those of M. charantia in PS-CK soil. Specifically, the changes in these physiological properties of M. charantia in MO_PA-RSD soil performed well than that in MO-RSD soil. The relative abundances of Cohnella, Effusibacillus, Rummeliibacillus, Oxobacter, Thermicanus, and Penicillium enriched in both RSD-treated soils were positively correlated with Paenibacillus and negatively correlated with F. oxysporum population and disease incidence (P < 0.05). Notably, the relative abundances of these potential probiotics were considerably higher in MO_PA-RSD-treated soil than in MO-RSD alone-treated soil. These results show that the RSD process with inoculation of Paenibacillus sp. could promote the colonization of this species and simultaneously stimulate the proliferation of other probiotic consortia to further enhance soil health and plant disease resistance.

Populus root exudates are associated with rhizosphere microbial communities and symbiotic patterns

Introduction

Microbial communities in the plant rhizosphere are critical for nutrient cycling and ecosystem stability. However, how root exudates and soil physicochemical characteristics affect microbial community composition in Populus rhizosphere is not well understood.

Methods

This study measured soil physiochemistry properties and root exudates in a representative forest consists of four Populus species. The composition of rhizosphere bacterial and fungal communities was determined by metabolomics and high-throughput sequencing.

Results

Luvangetin, salicylic acid, gentisic acid, oleuropein, strigol, chrysin, and linoleic acid were the differential root exudates extracted in the rhizosphere of four Populus species, which explained 48.40, 82.80, 48.73, and 59.64% of the variance for the dominant and key bacterial or fungal communities, respectively. Data showed that differential root exudates were the main drivers of the changes in the rhizosphere microbial communities. Nitrosospira, Microvirga, Trichoderma, Cortinarius, and Beauveria were the keystone taxa in the rhizosphere microbial communities, and are thus important for maintaining a stable Populus microbial rhizosphere. The differential root exudates had strong impact on key bacteria than dominant bacteria, key fungi, and dominant fungi. Moreover, strigol had positively effects with bacteria, whereas phenolic compounds and chrysin were negatively correlated with rhizosphere microorganisms. The assembly process of the community structure (keystone taxa and bacterial dominant taxa) was mostly determined by stochastic processes.

Discussion

This study showed the association of rhizosphere microorganisms (dominant and keystone taxa) with differential root exudates in the rhizosphere of Populus plants, and revealed the assembly process of the dominant and keystone taxa. It provides a theoretical basis for the identification and utilization of beneficial microorganisms in Populus rhizosphere.