Advanced Research of Rhizosphere Microbial Activity—Series II

A special issue of Agriculture (ISSN 2077-0472). This special issue belongs to the section "Agricultural Soils".

Deadline for manuscript submissions: closed (20 March 2024) | Viewed by 8872

Special Issue Editors

Centre for Agricultural Research, Institute for Soil Sciences, Herman O. út 15., 1022 Budapest, Hungary
Interests: soil biology; microbial ecology; sodic soils; karst soils; long-term experiments; restoration ecology
Special Issues, Collections and Topics in MDPI journals
Centre for Agricultural Research, Institute for Soil Sciences, Herman O. út 15., 1022 Budapest, Hungary
Interests: arbuscular mycorrhizal fungi (AMF); microbial inoculation; organic farming; long-term experiments; plant stress physiology; bioremediation/phytoremediation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The rhizosphere is one of the most important hotspots in soils and it harbors a huge number of microbial species, including archaea, bacteria and fungi. Root exudates serve as carbon and energy sources for heterotrophic microbes and have selective power to shape the microbial communities around root systems. The microbial activity of the rhizosphere can be one or two orders of magnitude higher than that of the surrounding bulk soil, and it is also a very dynamic and sensitive system. Microbes in the rhizosphere can aid plant nutrition and water uptake and promote plant growth by hormone and siderophore production; in addition, they can protect plants against pathogenic microbes, while in certain conditions some of them also become pathogenic. Climate change, land use change and different management options pose challenges to evaluating soil health in connection with plant–microbe interactions, and the microbial activity of the rhizosphere can be detected and measured in several ways. This Special Issue welcomes newly developed methods, such as community-level physiological profiling, the measurement of enzyme activity—alone or together with microbiome diversity by next-generation DNA sequencing—and other methodical approaches focusing on the microbial activity of the rhizosphere in all types of agricultural soils, including grassland and pasture soils.

Dr. Tibor Szili-Kovács
Dr. Tünde Takács
Guest Editors

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Keywords

  • rhizosphere
  • microbial activity
  • functional diversity
  • community-level physiological profile
  • soil health
  • bacterial and fungal community
  • PGPR bacteria
  • root exudates
  • root colonization
  • mycorrhizal fungi

Published Papers (4 papers)

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Research

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11 pages, 1233 KiB  
Article
Growth Performance and Osmolyte Regulation of Drought-Stressed Walnut Plants Are Improved by Mycorrhiza
by Yue Wen, Li-Jun Zhou, Yong-Jie Xu, Abeer Hashem, Elsayed Fathi Abd_Allah and Qiang-Sheng Wu
Agriculture 2024, 14(3), 367; https://doi.org/10.3390/agriculture14030367 - 25 Feb 2024
Viewed by 548
Abstract
This study aims to evaluate whether a selected arbuscular mycorrhizal fungus, Diversispora spurca, improves growth in drought-stressed walnut (Juglans regia L. cv. Qingxiang) plants and whether this improvement is associated with changes in osmolyte (fructose, glucose, sucrose, soluble protein, proline, and [...] Read more.
This study aims to evaluate whether a selected arbuscular mycorrhizal fungus, Diversispora spurca, improves growth in drought-stressed walnut (Juglans regia L. cv. Qingxiang) plants and whether this improvement is associated with changes in osmolyte (fructose, glucose, sucrose, soluble protein, proline, and betaine) levels. After 60 days of soil drought treatment (50% of maximum field water-holding capacity), root D. spurca colonization rate and soil mycelium length decreased by 13.57% and 64.03%, respectively. Soil drought also inhibited the growth performance of aboveground (stem diameter, leaf number, leaf biomass, and stem biomass) and underground (root projected area, surface area, and average diameter) parts, with uninoculated plants showing a stronger inhibition than D. spurca-inoculated plants. D. spurca significantly increased these growth variables, along with aboveground part variables and root areas being more prominent under drought stress versus non-stress conditions. Although drought treatment suppressed the chlorophyll index and nitrogen balance index in leaves, mycorrhizal inoculation significantly increased these indices. Walnut plants were able to actively increase leaf fructose, glucose, sucrose, betaine, and proline levels under such drought stress. Inoculation of D. spurca also significantly increased leaf fructose, glucose, sucrose, betaine, proline, and soluble protein levels under drought stress and non-stress, with the increasing trend in betaine and soluble protein being higher under drought stress versus non-stress. Drought stress dramatically raised leaf hydrogen peroxide (H2O2) levels in both inoculated and uninoculated plants, while mycorrhizal plants presented significantly lower H2O2 levels, with the decreasing trend higher under drought stress versus non-stress. In conclusion, D. spurca symbiosis can increase the growth of drought-stressed walnut plants, associated with increased osmolyte levels and decreased H2O2 levels. Full article
(This article belongs to the Special Issue Advanced Research of Rhizosphere Microbial Activity—Series II)
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11 pages, 2404 KiB  
Article
Serendipita indica: A Biostimulant Enhancing Low-Temperature Tolerance and Active Constituent Levels in Polygonum cuspidatum
by Junhao Shen and Yongqin Chen
Agriculture 2024, 14(1), 7; https://doi.org/10.3390/agriculture14010007 - 20 Dec 2023
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Abstract
Polygonum cuspidatum is a traditional medicinal plant enriched with resveratrol and polydatin. However, low temperatures reduce the medicinal component contents of P. cuspidatum, and prolonged low temperatures also affect the growth and survival of P. cuspidatum at the seedling stage. It is [...] Read more.
Polygonum cuspidatum is a traditional medicinal plant enriched with resveratrol and polydatin. However, low temperatures reduce the medicinal component contents of P. cuspidatum, and prolonged low temperatures also affect the growth and survival of P. cuspidatum at the seedling stage. It is unclear whether a culturable endophytic fungus Serendipita indica is able to enhance P. cuspidatum’s low-temperature tolerance and medicinal components. The objective of this study was to examine the biomass, leaf gas exchange, antioxidant enzyme activity, proline levels, medicinal constituent levels, and the expression of the resveratrol synthase (PcRS) and resveratrol-forming stilbene synthase 11 (PcRS11) genes of potted P. cuspidatum plants inoculated with S. indica at low temperatures (10 °C/6 °C, 12 h/12 h, day/night temperature). The six-week low-temperature treatment significantly reduced the root fungal colonization, biomass production, and leaf gas exchange variables, whereas S. indica inoculation significantly increased shoot and root biomass, photosynthetic rate, stomatal conductance, and transpiration rate at low temperatures. S. indica inoculation significantly increased superoxide dismutase and catalase activity as well as proline levels in leaves at low temperatures. The magnitude of root chrysophanol, emodin, polydatin, and resveratrol levels decreased by low temperatures was greater in uninoculated plants than in inoculated plants. Inoculation of S. indica, on the other hand, significantly increased the four medicinal component levels in roots at low temperatures, with a greater magnitude rise in chrysophanol, polydatin, and resveratrol at low temperatures than at suitable temperatures. The low-temperature treatment down-regulated the expression of PcRS and PcRS11 genes in roots, while S. indica up-regulated the expression of PcRS and PcRS11 genes at low temperatures. This implies that S. indica acts as a powerful microbial stimulant on P. cuspidatum to promote low-temperature resistance and medicinal component levels. Full article
(This article belongs to the Special Issue Advanced Research of Rhizosphere Microbial Activity—Series II)
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18 pages, 3056 KiB  
Article
Effects of Altitude and Continuous Cropping on Arbuscular Mycorrhizal Fungi Community in Siraitia grosvenorii Rhizosphere
by Limin Yu, Zhongfeng Zhang, Longwu Zhou and Kechao Huang
Agriculture 2023, 13(8), 1548; https://doi.org/10.3390/agriculture13081548 - 02 Aug 2023
Cited by 1 | Viewed by 2158
Abstract
Siraitia grosvenorii, a medicinal plant with continuous cropping, is cultivated in southern China. Changes in the soil microbial community during continuous cropping can cause soil-borne diseases in S. grosvenorii. This experimental study aimed to determine the differences in the arbuscular mycorrhizal [...] Read more.
Siraitia grosvenorii, a medicinal plant with continuous cropping, is cultivated in southern China. Changes in the soil microbial community during continuous cropping can cause soil-borne diseases in S. grosvenorii. This experimental study aimed to determine the differences in the arbuscular mycorrhizal fungi (AMF) community structure and root colonization in the rhizosphere soil of S. grosvenorii with different continuous cropping years and altitudes. We tested three altitude gradients (low, 200–300 m; middle, 500–600 m; and high, 700–800 m) and four continuous cropping years (1, 2, 3, and 5 years). AMF colonization, along with AMF spore density, and the soil physicochemical properties of S. grosvenorii roots at different altitudes and continuous cropping years were determined. Illumina high-throughput sequencing was used to determine the molecular diversity of AMF in the rhizosphere of S. grosvenorii as they exhibited a symbiotic relationship. The AMF species in the rhizosphere soil of S. grosvenorii included 28 species of nine genera, including Glomus, Claroideoglomus, Acaulospora, Paraglomus, Ambispora, and so on. With an increasing altitude, the AMF colonization of S. grosvenorii roots increased significantly (p < 0.01); available phosphorus (AP) content was negatively correlated with AMF colonization (p < 0.01). Glomus and Paraglomus were the common dominant genera in the rhizosphere soil of S. grosvenorii planted for 2–5 years at a low altitude and 1 year at middle and high altitudes. The average relative abundance of Glomus increased with increasing continuous cropping years and altitude in the low-altitude and 1-year S. grosvenorii areas, respectively. Slightly acidic rhizosphere soil contributed to AMF colonization and improved the richness and diversity of the AMF community. Our results showed that altitude, AP, and pH are essential factors for predicting AMF infection and community changes in the S. grosvenorii rhizosphere. Here, Illumina high-throughput sequencing was used to study the species resources and community composition of mycorrhizal fungi in S. grosvenorii in the hilly areas of Guangxi, China. This study provides a theoretical basis for the application and practice of mycorrhizal fungi including the isolation and screening of dominant strains, inoculation of mycorrhizal fungi, and exploration of the effects of mycorrhizal fungi on the growth and active ingredients of medicinal plants. Full article
(This article belongs to the Special Issue Advanced Research of Rhizosphere Microbial Activity—Series II)
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Review

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21 pages, 1575 KiB  
Review
Rhizobia: A Promising Source of Plant Growth-Promoting Molecules and Their Non-Legume Interactions: Examining Applications and Mechanisms
by Sara Fahde, Said Boughribil, Badreddine Sijilmassi and Ahmed Amri
Agriculture 2023, 13(7), 1279; https://doi.org/10.3390/agriculture13071279 - 21 Jun 2023
Cited by 10 | Viewed by 5166
Abstract
For over a century, the scientific community has had a comprehensive understanding of how rhizobia can promote the growth of legumes by forming nitrogen fixing nodules. Despite this knowledge, the interaction of rhizobia with non-legumes has remained largely ignored as a subject of [...] Read more.
For over a century, the scientific community has had a comprehensive understanding of how rhizobia can promote the growth of legumes by forming nitrogen fixing nodules. Despite this knowledge, the interaction of rhizobia with non-legumes has remained largely ignored as a subject of study until more recent decades. In the last few years, research has shown that rhizobia can also associate with non-legume roots, which ultimately leads to the stimulation of growth through diverse direct and indirect mechanisms. For example, rhizobia can enhance growth through phytohormones production, the improvement of plant nutrient uptake, such as the solubilization of precipitated phosphorus, the production of siderophores to address iron needs, and also the reduction of ethylene levels through the ACC deaminase enzyme to cope with drought stress. Additionally, rhizobia can improve, indirectly, non-legume growth through biocontrol of pathogens and the induction of systemic resistance in the host plant. It can also increase root adherence to soil by releasing exopolysaccharides, which regulate water and soil nutrient movement. The objective of this review is to assess and analyze the existing knowledge and information regarding the mechanisms through which rhizobia promote the growth of non-legumes. By conducting a comprehensive analysis of these findings, we aim to gain new insights into the development of Rhizobium/non-legume interactions. Full article
(This article belongs to the Special Issue Advanced Research of Rhizosphere Microbial Activity—Series II)
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