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Agronomy
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Rhizosphere Microorganisms
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Rhizosphere Microorganisms

A special issue of Agronomy (ISSN 2073-4395). This special issue belongs to the section "Agricultural Biosystem and Biological Engineering".

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 13056

Special Issue Editor

Prof. Dr. Zhihong Xie

E-Mail Website
Guest Editor
National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer Resources, College of Resources and Environment, Agricultural University of Shandong, Tai'an 271000, China
Interests: plant rhizosphere microorganisms; plant–microbe interactions
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Plant rhizosphere microorganisms can protect against pathogens, improve growth and contribute to plant phenotypic plasticity. Plant growth-promoting rhizobacteria (PGPR) are beneficial microbes that stably survive and colonize in the rhizosphere of plants. PGPR are the major source of biofertilizer strains, which show beneficial effects on crops, such as growth promotion, inhibition of soil-borne pathogens and enhancement of plant tolerance. The beneficial functions of PGPR on plants largely rely on root colonization ability, for which chemotactic motility and biofilm formation on the rhizoplane are the most important colonization processes. This provides a rational basis for increasing the quality of soil and developing sustainable agriculture with less input of fertilizers or pesticides.

Prof. Dr. Zhihong Xie
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • rhizosphere
  • microorganisms
  • interaction
  • promote
  • resistance

Published Papers (7 papers)

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Editorial

Jump to: Research

5 pages, 232 KiB  
Editorial
Developing Plant-Growth-Promoting Rhizobacteria: A Crucial Approach for Achieving Sustainable Agriculture
by Dandan Wang, Chao Wang, Yinglong Chen and Zhihong Xie
Agronomy 2023, 13(7), 1835; https://doi.org/10.3390/agronomy13071835 - 11 Jul 2023
Viewed by 1110
Abstract
The rhizosphere is the zone surrounding plant roots where microbial activity attains its maximum potential, playing pivotal roles in maintaining plant health [...] Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)

Research

Jump to: Editorial

17 pages, 10133 KiB  
Article
Microbiocenosis of the Permafrost Soils of Transbaikalia under Agriculture Use
by Tsypilma Korsunova, Erzhena Chimitdorzhieva, Galina Chimitdorzhieva, Maria Merkusheva, Yurii Tsybenov, Elena Valova and Nimbu Baldanov
Agronomy 2023, 13(11), 2740; https://doi.org/10.3390/agronomy13112740 - 30 Oct 2023
Viewed by 1140
Abstract
An understanding of how the involvement of soils in agricultural turnover affects soil microbiocenosis has been attained. The aims of this study were to investigate the number of the main groups of microorganisms in microbial complexes, the carbon of microbial biomass and the [...] Read more.
An understanding of how the involvement of soils in agricultural turnover affects soil microbiocenosis has been attained. The aims of this study were to investigate the number of the main groups of microorganisms in microbial complexes, the carbon of microbial biomass and the enzymatic activity in permafrost soils under the influence of tillage. The presented data can provide an insight into the stability of the microbiome in region’s soils under agricultural influence. The significance of the study lies in obtaining new data on the microbiocenosis of permafrost soils, which will make it possible to reveal the orientation and intensity of microbiological processes during their agricultural use. The study uses the classical methods used in soil science and soil microbiology, which are characterized by accuracy and reliability. The general characteristics of the microbiocenosis of different types of the studied region’s soils have been revealed. The quantity of bacteria, including actinomycetes and fungi, in the studied soils was determined. The variability of indicators in time and space is shown. The number of bacteria was revealed to reach its maximum in the autumn period in grey forest non-podzolised soils, and the indicator decreases in the following manner: forest—10.6 billion cells/g, arable land—5.1 billion cells/g, virgin land—2.6 billion cells/g. The lowest indicator of bacterial abundance—0.5 billion cells/g was found on arable permafrost meadow chernozemic soil. A comparatively low bacterial content is characteristic of chernozem meal-carbonated: 1.9 billion cells/g on virgin land and 2.1 billion cells/g on arable land. The length of actinomycete mycelium is dynamic according to the seasons of the year. The maximum length of actinomycete mycelium was observed in grey forest non-podzolised soil (forest) in the autumn period—830 m/g. The maximum length of fungal mycelium was also observed in grey forest non-podzolised soil (forest) in autumn—1200 m/g. In arable variants, the length of fungal mycelium is high in grey forest non-podzolised soils and meadow permafrost soils. In chernozems and permafrost meadow chernozemic soils (virgin and arable) the index is much lower. Assessment of catalase activity showed that the studied soils are poor or moderately enriched in this enzyme. Relatively high invertase activity was found in all variants. Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)
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13 pages, 1241 KiB  
Article
Effects of Inoculation with Different Plant Growth-Promoting Rhizobacteria on the Eco-Physiological and Stomatal Characteristics of Walnut Seedlings under Drought Stress
by Dawei Jing, Binghua Liu, Hailin Ma, Fangchun Liu, Xinghong Liu and Liying Ren
Agronomy 2023, 13(6), 1486; https://doi.org/10.3390/agronomy13061486 - 28 May 2023
Cited by 3 | Viewed by 1698
Abstract
Plant growth-promoting rhizobacteria (PGPR) can promote plant growth and induce systemic resistance to biological and abiotic stresses. However, do all PGPR have significant effects in arid environments, and which PGPR have the most optimal effects? This study used a pot experiment to investigate [...] Read more.
Plant growth-promoting rhizobacteria (PGPR) can promote plant growth and induce systemic resistance to biological and abiotic stresses. However, do all PGPR have significant effects in arid environments, and which PGPR have the most optimal effects? This study used a pot experiment to investigate the effects of inoculation with two different PGPR on the physiological and ecological characteristics of walnut (Juglans regia) seedlings under drought stress: Bacillus subtilis GE1, which secretes protease only, and Pseudomonas brassicacearum X123, which secretes protease and indoleacetic acid (IAA). The leaves inoculated with X123 under drought stress had higher net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (gs), especially stomatal length and stomatal width, compared to GE1 inoculation under drought stress. Moreover, inoculation with X123 significantly increased the leaf superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities by 20.84% and 12.41%, respectively, and the gibberellin (GA) and zeatin (ZT) contents by 72.07% and 19.17%, respectively, whereas the leaf soluble sugar and soluble protein contents significantly decreased compared with GE1 inoculation. These results indicated that the effects of GE1 inoculation on the physiological and ecological characteristics of walnut seedling leaves were significantly weaker in comparison with X123 inoculation as a result of its functional characteristics. The application of different PGPR on the drought tolerance of J. regia showed significant differences. Therefore, the selection of appropriate PGPR is key to achieving positive treatment effects under drought conditions. Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)
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15 pages, 2049 KiB  
Article
Effect of Salt Stress on Microbiome Structure and Diversity in Chamomile (Matricaria chamomilla L.) Rhizosphere Soil
by Fei Xia, Haiping Hao, Ying Qi, Hongtong Bai, Hui Li, Zhenxia Shi and Lei Shi
Agronomy 2023, 13(6), 1444; https://doi.org/10.3390/agronomy13061444 - 24 May 2023
Cited by 2 | Viewed by 1481
Abstract
Chamomile (Matricaria chamomilla L.) is an economically valuable plant with certain salt alkali adaptability. Here, we aim to understand how salt stress affects both the structure and diversity of the soil microbial community and how root exudates may mediate this response. The [...] Read more.
Chamomile (Matricaria chamomilla L.) is an economically valuable plant with certain salt alkali adaptability. Here, we aim to understand how salt stress affects both the structure and diversity of the soil microbial community and how root exudates may mediate this response. The results showed that high salt stress treatment reduced the overall diversity and abundance of both bacteria and fungi but did not alter the presence or abundance of dominant phyla, including Proteobacteria, Acidobacteriota, and Ascomycota. Several microbial species belonging to Geminicoccaceae, Rokubacteriaces, and Funneliformis-sp were found to be highly resistant to salt stress, while others were found to be highly sensitive, including Xanthobacteraceae, JG30-KF-AS9-sp, and Asperellum. Redundancy analysis results showed that bacteria tended to be more sensitive to the presence of salt ions in the soil, including SO42−, Ca2+, and Na+, while fungi were more sensitive to the presence of certain root exudates, including methyl 4-methylbenzoate, δ-selinene. It suggested that the presence of a relatively stable set of dominant phyla and the increased abundance of salt-tolerant species and their ecological functions may be related to the tolerance of chamomile to salt stress. The results will underpin future improvement in chamomile to coastal salinity soil tolerance through altering the soil microbial community. Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)
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15 pages, 3201 KiB  
Article
The Two Chemotaxis Gene Clusters of Ensifer alkalisoli YIC4027T, a Symbiont of Sesbania cannabina, Play Different Roles in Chemotaxis and Competitive Nodulation
by Tingting Guo, Yanan Zhou, Zhihong Xie and Fankai Meng
Agronomy 2023, 13(2), 570; https://doi.org/10.3390/agronomy13020570 - 16 Feb 2023
Cited by 2 | Viewed by 1183
Abstract
Ensifer alkalisoli YIC4027T is a dominant rhizobium that has been isolated from the root nodules of Sesbania cannabina. Motility and chemotaxis are critical to maintaining competitiveness in establishing the symbiotic relationship. E. alkalisoli carries two gene clusters, che1 and che2, [...] Read more.
Ensifer alkalisoli YIC4027T is a dominant rhizobium that has been isolated from the root nodules of Sesbania cannabina. Motility and chemotaxis are critical to maintaining competitiveness in establishing the symbiotic relationship. E. alkalisoli carries two gene clusters, che1 and che2, containing chemotaxis-related gene homologues. To determine the respective role of each gene cluster, we constructed mutants and compared them with the wild type in a free-living state and in symbiosis with the host plant. A swimming analysis revealed that the che1 cluster was the major pathway controlling the chemotaxis and swimming bias, while the che2 cluster had a minor role in these behaviors. However, the Δche2 mutant was impaired in exopolysaccharide (EPS) production. During symbiosis, the Δche1 mutant was more severely impaired in its competitive root colonization and nodulation ability than the Δche2 mutant. Taken together, our data strongly suggested that both of the che clusters contribute to the competitive symbiotic association, the che1-like homologue being the main regulator of the chemotactic response and the che2 cluster regulating EPS production. These data illustrated a novel strategy of motile rhizobia bacteria to utilize the two pathways containing the homologous genes to enhance the efficiency of nodule formation by regulating distinct motility parameters or other cellular functions. Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)
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10 pages, 978 KiB  
Article
Plant-Growth-Promoting Rhizobacteria Improve Germination and Bioactive Compounds in Cucumber Seedlings
by Laura-Andrea Pérez-García, Jorge Sáenz-Mata, Manuel Fortis-Hernández, Claudia Estefanía Navarro-Muñoz, Rubén Palacio-Rodríguez and Pablo Preciado-Rangel
Agronomy 2023, 13(2), 315; https://doi.org/10.3390/agronomy13020315 - 20 Jan 2023
Cited by 11 | Viewed by 3604
Abstract
Plant-growth-promoting rhizobacteria (PGPR) increase the germination percentage and the vigor of seeds, thus determining aspects for the efficient production of seedlings and the prompt establishment of crops in the field. In this study, the effect of the biopriming of rhizobacteria was evaluated: Bacillus [...] Read more.
Plant-growth-promoting rhizobacteria (PGPR) increase the germination percentage and the vigor of seeds, thus determining aspects for the efficient production of seedlings and the prompt establishment of crops in the field. In this study, the effect of the biopriming of rhizobacteria was evaluated: Bacillus cereus (KBEndo4P6), Acinetobacter radioresistens (KBEndo3P1), Pseudomonas paralactis (KBEndo6P7), and Sinorhizobium meliloti (KBEkto9P6) on some parameters such as the percentage of germination and vigor and the germination index, among others, as well as the synthesis of phytocompounds in the seeds of Cucumis sativus L. biopriming seeds significantly improved germination, the germination index, the vigor, the plumule and the radicle length, in addition to an increase in phytochemical compounds. The rhizobacteria KBEndo3P1 increased the germination percentage by 20%, the germination index by 50%, and the seed vigor by 60%, as well as the length of the radicle by 11%, and the plumule by 48% compared to the control, and the total phenols and antioxidants increased by 9% and 29%, respectively. Biopriming with plant-growth-promoting rhizobacteria increases germination, which allows for the possibility of more outstanding production of seedlings and a greater length of the radicle, thus increasing the efficiency in the processes of water and nutrient absorption and improving its establishment in the field. In addition, the production of phytocompounds enhances their response against any type of stress, making them a viable alternative in sustainable agriculture to increase cucumber yield. Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)
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12 pages, 628 KiB  
Article
Effects of Plant Growth-Promoting Rhizobacteria on the Physioecological Characteristics and Growth of Walnut Seedlings under Drought Stress
by Fangchun Liu, Hailin Ma, Binghua Liu, Zhenyu Du, Bingyao Ma and Dawei Jing
Agronomy 2023, 13(2), 290; https://doi.org/10.3390/agronomy13020290 - 18 Jan 2023
Cited by 11 | Viewed by 2045
Abstract
Drought is one of the most brutal environmental factors limiting the productivity of fruit trees. The search for new and efficient microorganisms from unexplored environments that can be used to mitigate the negative effects of water stress is an interesting alternative to alleviate [...] Read more.
Drought is one of the most brutal environmental factors limiting the productivity of fruit trees. The search for new and efficient microorganisms from unexplored environments that can be used to mitigate the negative effects of water stress is an interesting alternative to alleviate the drought stress experienced by plants. This study aimed to determine the effects of PGPR inoculation on the growth and physioecological characteristics of walnut (Juglans regia) seedlings under drought stress. A pot experiment was conducted using J. regia seedlings with controlled water supplies at different levels (light, moderate, and severe drought stress and control) and with or without inoculation with Bacillus cereus L90, a type of PGPR that produces high levels of cytokinins and indoleacetic acid (IAA). Under well-watered conditions, there was no obvious effect of PGPR inoculation on the antioxidant enzyme activities, osmotic adjustment levels, and photosynthetic characteristics of J. regia. As the stress intensity increased, B. cereus inoculation increased the antioxidant enzyme activities in walnut seedlings and changed their photosynthetic characteristics. However, levels of osmotic adjustment substances were decreased as a result of PGPR inoculation. Regardless of water status, B. cereus inoculation induced a significant increase in IAA, gibberellins, and zeatin contents in J. regia. Under well-watered and light stress conditions, the abscisic acid content of walnut was significantly increased by B. cereus inoculation. Additionally, B. cereus inoculation significantly promoted the growth of plants in terms of ground diameter and plant height. As a result, PGPR inoculation could improve the drought resistance of J. regia and improve its photosynthetic characteristics and growth, suggesting that it is a useful supplementary measure for use in afforestation in arid and semiarid environments. Full article
(This article belongs to the Special Issue Rhizosphere Microorganisms)
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