Root Colonization Research Articles

Induced Drought Stress Response of European Beech Seedlings Treated with Hydrogel and Ectomycorrhizal Inoculum

Bareroot European beech (Fagus sylvatica L.) seedlings are frequently used in reforestation programs in Central Europe. However, beech outplanting is often unsuccessful due to drought stress. In this study, the effects of a simulated water deficit and of a hydrogel and ectomycorrhizal fungi (EMF) application were estimated on the development of 1 + 1 beech seedlings. The roots of 1-year-old bareroot seedlings were treated with the additives at the time of transplanting to pots in spring and then exposed to the whole growing season under different watering regimes: (i) full watering (FW; volumetric water content 70%), (ii) reduced watering (RW; 40%), (iii) periodic watering (PW; substrate rewetted to 70% after drying), and (iv) no watering (NW). Almost all FW seedlings survived the whole growing season, whereas all NW seedlings died after 17 weeks of desiccation. The survival and growth of FW and NW seedlings were significantly higher and lower, respectively, than those under both PW and RW treatments. The additives significantly increased survival in RW seedlings only but had no effect on growth. A promoting effect of FW on the chlorophyll a fluorescence parameters was found. The number and EMF colonization of the short roots were significantly lower in FW seedlings compared to the other watering treatments. The additives did not affect these parameters. The occurrence of neither treatment-specific EMF root morphotype nor fungi applied in the inoculum and traced by molecular analysis indicated the formation of ectomycorrhizas with native EMF in all treatments. The seedlings in the water-deficient treatments exhibited higher foliar nutrient concentrations than FW seedlings. The additives increased the concentration of nutrients in PW and phosphorus in NW seedlings. The results suggest the significant effect of the water supply, but a weaker effect of the additives tested on beech seedling development under experimental conditions.

Colonization potential of endophytes from halophytic plants growing in the "Runn of Kutch" salt marshes and their contribution to mitigating salt stress in tomato cultivation.

Increasing soil salinity depreciates the quantity of the crop produce. Looking at the tremendous potential of plant-associated microorganisms in salinity stress mitigation, it would be very useful in exploring and deciphering salt-tolerant microorganisms from halophytic plants and their utilization in cultivated plants. With this aim, in the present study, four halophytic plants were taken from Rann of Kutch, and bacterial endophytes were isolated from different plant organs. These endophytes were characterized by plant growth and health promotion features. The molecular identification was done based on 16 s rRNA sequence similarity. It was found that the endophytic bacteria isolated from 4 different halophytes found sharing phylogenetic relatedness. Four potential endophytes Alkalihalobacillus gibsonii 2H2, Achromobacter insuavis 2H18, Terribacillus halophilus 2H20, and Bacillus siamensis 4H1 were tested in tomato for salinity stress alleviation. Changes in the levels of antioxidants were analyzed. Total chlorophyll, total phenolics, malondialdehyde, and proline content indicated reduced damage in the plant system due to salinity by the application of endophytes. All the treatments exhibited low levels of electrolyte leakage. The accumulation of enzymatic reactive oxygen species scavengers was assessed from the levels of peroxidase, catalase, superoxide dismutase, phenylalanine ammonia-lyase, ascorbate peroxidase, and guiacol peroxidase. The NBT and DAB staining confirmed the findings. The reduction in the accumulation of Na+ ions in tomato leaves was visualized using Sodium Green probes under CSLM and found to be lowest in Terribacillus halophilus 2H20 and Bacillus siamensis 4H1 inoculated plants. The endophyte Terribacillus halophilus 2H20 was the most promising isolate. The colonization in tomato roots was confirmed using a cell tracker system. Results showed that the endophytes were found to have salinity stress mitigation traits. The efficiency could be further improved with the combination of other endophytes tested earlier.

Function of the endophytic fungus Acrophialophora jodhpurensis, methionine, and nitric oxide in wheat resistance induction against Fusarium graminearum via interplay of reactive oxygen species and iron

In this study, the effect of Acrophialophora jodhpurensis, methionine, and sodium nitroprusside (as a NO donor) in induction of resistance against Fusarium graminearum, as a hemibiotrophic phytopathogenic fungus causing wheat root and crown rot, was investigated in vivo. Also, the effect of A. jodhpurensis was investigated on the mycelial growth, spore germination and hyphal structures of F. graminearum in vitro. The obtained results showed that A. jodhpurensis reduced mycelial growth and spore germination of the pathogen. Also, the spores and hyphae of the pathogen were swollen and deformed in the presence of A. jodhpurensis. Wheat root colonization by A. jodhpurensis and foliar application of methionine and sodium nitroprusside reduced the disease severity of F. graminearum and increased the plant growth parameters, such as shoot and root weight compared to the controls. Application of A. jodhpurensis, methionine and sodium nitroprusside had a significant effect in induction of resistance against F. graminearum via increasing superoxide (O2⋅-), hydrogen peroxide (H2O2), iron ions, phenolic contents, induction of antioxidant enzymes such as catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities, membrane stability index (MSI) and relative water content (RWC) compared to the plants only inoculated with F. graminearum and uninoculated controls. Simultaneous application of A. jodhpurensis and sodium nitroprusside was more effective than simultaneous application of A. jodhpurensis and methionine. Also, simultaneous application of A. jodhpurensis, methionine and sodium nitroprusside treatments showed more effect on the plant growth parameters and resistance induction against the pathogen compared to the other treatments. Therefore, the combined A. jodhpurensis, methionine and sodium nitroprusside treatment can be used for increasing the plant growth parameters and protecting wheat plants against F. graminearum.

Genomic content of wheat has a higher influence than plant domestication status on the ability to interact with Pseudomonas plant growth-promoting rhizobacteria.

Plant evolutionary history has had profound effects on belowground traits, which is likely to have impacted the ability to interact with microorganisms, but consequences on root colonization and gene expression by plant growth-promoting rhizobacteria (PGPR) remain poorly understood. Here, we tested the hypothesis that wheat genomic content and domestication are key factors determining the capacity for PGPR interaction. Thus, 331 wheat representatives from eight Triticum or Aegilops species were inoculated under standardized conditions with the generalist PGPR Pseudomonas ogarae F113, using an autofluorescent reporter system for monitoring F113 colonization and expression of phl genes coding for the auxinic inducing signal 2,4-diacetylphloroglucinol. The interaction with P. ogarae F113 was influenced by ploidy level, presence of genomes AA, BB, DD, and domestication. While root colonization was higher for hexaploid and tetraploid species, and phl expression level higher for hexaploid wheat, the diploid Ae. tauschii displayed higher phl induction rate (i.e., expression:colonisation ratio) on roots. However, a better potential of interaction with F113 (i.e., under non-stress gnotobiotic conditions) did not translate, after seed inoculation, into better performance of wheat landraces in non-sterile soil under drought. Overall, results showed that domestication and especially plant genomic content modulate the PGPR interaction potential of wheats.

Electrical Conductivity and pH Are Two of the Main Factors Influencing the Composition of Arbuscular Mycorrhizal Fungal Communities in the Vegetation Succession Series of Songnen Saline-Alkali Grassland.

Arbuscular mycorrhizal fungi (AMF) are widely distributed microorganisms in the soil, playing an important role in vegetation succession, plant community diversity, and improving soil physicochemical properties. In this study, morphological identification and high-throughput sequencing technology were used to comprehensively analyze the AMF community composition and diversity at different succession stages of Songnen saline-alkali grassland. To determine the root colonization status of plants collected in the field, a colonization system was established using late-succession plants as host plants to verify the existence of mycorrhizal symbiosis and the matching phenomenon of AMF in Songnen saline-alkali grassland. The results indicated that both morphological methods and high-throughput sequencing technology showed that glomus was the dominant genus of AMF in Songnen saline grassland. Redundancy analysis (RDA) and linear regression analysis showed that electrical conductivity (EC) and pH were the main environmental factors affecting AMF species diversity and community structure in the succession sequence of Songnen saline grassland. In addition, the results of root colonization identification and the colonization system test in the field showed that AMF successfully colonized vegetation at different succession stages and had mycorrhizal symbiosis. The results of this study could help to understand the AMF community of Songnen saline-alkali grassland as well as provide a reference and basis for optimizing the AMF community structure of Songnen saline-alkali grassland through human intervention in the future and using mycorrhizal technology to restore and rebuild the degraded ecosystem of Songnen saline-alkali grassland.

Intercropping and weed cover reduce sugarcane roots colonization in plant crops as a result of spatial root distribution and the co-occurrence of neighboring plant species

Intercropping and weed cover reduce sugarcane roots colonization in plant crops as a result of spatial root distribution and the co-occurrence of neighboring plant species

Regulation of mycorrhizal colonization under stress in tomato depends on symbiotic efficiency

The mutualistic symbiosis between plants and arbuscular mycorrhizal (AM) fungi is based on a balanced nutrient exchange between both partners, with the plant achieving improved nutrition and stress tolerance. The symbiosis is finely-tuned according to plant’s needs and surrounding conditions, usually through phytohormonal signaling. Thus, environmental conditions or stress factors modulating phytohormone signaling may influence the symbiosis. This study compares the colonization abilities of 2 AM fungal species, Funneliformis mosseae and Rhizophagus irregularis, independently or in combination, in tomato plants subjected to different stress conditions. These included salt stress and systemic defense activation by aboveground application of the defense-related hormones methyl jasmonate, abscisic acid and salicylic acid. The results show that root colonization by the two fungal species differs depending on the stress treatment. Nutrient and transcriptional analyses revealed that changes in colonization correlated with differential regulation of nutrient exchange, plant defensive responses, and symbiosis regulatory genes. Specifically, under salt stress R. irregularis colonization decreased, while F. mosseae colonization was promoted. These differential regulation of colonization under stress positively correlated with changes in the functionality of the symbiosis. Overall, the results support that the benefits provided by each AM fungi influence carbon reward and determines the control of root colonization by the host plant.

Unraveling the mechanisms of drought tolerance enhancement in Sorghum bicolor through Glomus mosseae inoculation: Insights from comparative analysis of Super 2 and Konawe Selatan accessions

The increasing frequency of droughts due to climate change has negatively impacted crop yield. This research aimed to study the mechanism of Glomus mosseae in improving the drought tolerance of Sorghum bicolor plants, specifically in Super 2 (S2) and Konawe Selatan (KS) accession. G. mosseae was used to inoculate the plants grown in the sterile zeolite. The drought was imposed in two cycles by suspending irrigation for six days per cycle. After nine weeks, the plants were harvested and subjected to various analyses. The results showed that drought stress lowered biomass, pigment concentrations by 45% and 23%, and leaf relative water content (RWC) by 34% and 17% for S2 and KS accessions, respectively. Conversely, malondialdehyde (MDA) levels rose by 20% and 9%, while proline synthesis was improved by 7% and 16% on S2 and KS, respectively, compared to the control. In contrast, inoculation with G. mosseae markedly augmented chlorophyll levels by 85% and 25%, elevated leaf relative water content by 33% and 8%, and enhanced P content by 20% and 19% for S2 and KS accessions, respectively, when compared to drought-exposed treatments. Additionally, G. mosseae inoculation preserved root length, biomass, leaf number, proline synthesis, and nitrogen content, while inducing a reduction in MDA levels by 11% and 6% in S2 and KS, respectively, in relation to the drought treatments. G. mosseae improves sorghum's drought tolerance by reducing water loss through improving water and nutrient uptake via external hyphae and enhancing photosynthetic properties via pigment protection. Furthermore, it was shown that G. mosseae is highly efficient at maintaining proline balance and enhancing the effectiveness of both enzymatic and non-enzymatic antioxidants to eliminate reactive oxygen species (ROS). KS accession exhibited elevated levels of nitrogen content, leaf number, upper ground biomass, chlorophyll and RWC. Conversely, the Super 2 accession manifested higher levels of lower ground biomass, root length, root colonization and phosphorus content. The addition of G. mosseae to the soil shows great potential as a sustainable agricultural approach under climate change conditions, specifically for the promotion of sorghum plant survival under drought stress. This potential stems from the ability of G. mosseae to enhance key plant properties, including photosynthetic performance and water balance regulation, through the expansion of extraradical hyphal growth. Moreover, G. mosseae supplementation maintains proline levels, enhances nutrient uptake and detoxifies reactive oxygen species by promoting antioxidant capacity. As a result of these properties, sorghum plants exhibit increased biomass and resistance to drought stress, providing an important tool for future sustainable agriculture under climate change.

Unravelling the Combined Use of Soil and Microbial Technologies to Optimize Cultivation of Halophyte Limonium algarvense (Plumbaginaceae) Using Saline Soils and Water

Salt-affected soils have detrimental effects on agriculture and ecosystems. However, these soils can still be used for halophyte (salt-tolerant plants) cultivation using brackish and/or saline water. In this study, we employed soil technologies and mutualistic microorganisms as a sustainable strategy to improve the growth and reproduction of the halophyte Limonium algarvense Erben’s growth and reproduction under saline conditions. A microcosm assay was conducted under controlled greenhouse conditions to cultivate L. algarvense using a saline Fluvisol (FLU) amended—or not—with a Technosol (TEC). Plants were inoculated with the arbuscular mycorrhizal fungus (AMF) Rhizoglomus irregulare and/or a consortium of plant growth-promoting bacteria (PGPB), and they were irrigated with estuarine water. Soil enzyme analysis and physicochemical characterisation of the soils, collected at the beginning and at the end of the assay, were carried out. The physiological status of non-inoculated and inoculated plants was monitored during the assay for 4 months, and AMF root colonisation was evaluated. In FLU, only plants inoculated with the AMF survived. These plants had lower number of leaves, and shoot and root dry biomass than the ones grown in the TEC by the end of the assay. In the TEC, PGPB inoculation led to higher NDVI and PRI values, and AMF inoculation promoted higher reproductive development but not pollen fertility. The findings show that the combined use of soil and microbial technologies can be successfully applied to cultivate L. algarvense, suggesting their generalized use for other Limonium species with economic interest, while contributing to the sustainable use of marginal lands.

Arbuscular mycorrhizal characterization associated with Uncaria guianensis and Uncaria tomentosa in Amazonian soils

There are some plant species with cultural and economic importance in the Amazon, such as Uncaria guianensis and U. tomentosa, both commonly named “cat's claw”. Since these species grow in soils with low levels of organic matter and nutrients, both depend on arbuscular mycorrhizae to grow. The information about arbuscular mycorrhizal fungi communities for U. tomentosa is limited and there is no current research on U. guianensis. Therefore, this research provides additional information on the arbuscular mycorrhizal fungi communities associated with Uncaria species in Amazonian soils. Both the percentage of root colonization and the influence of the edaphic composition in the two species were determined. Also, the richness and diversity of arbuscular mycorrhizal fungi were assessed using the spore isolation method and also, through the molecular analysis of virtual taxa. In addition, the difference between the soils was analyzed. Although U. guianensis grows in both Oxisols and Alluvial Entisols and U. tomentosa is restricted to Oxisols, sporulation of AM and root colonization does not respond significantly to variations in soil chemical properties. Additionally, 72 virtual taxa were identified for Uncaria species (53 U. tomentosa and 19 U. guianensis) and the relative abundance of arbuscular mycorrhizal fungi was higher in roots of Uncaria species than in soils. The arbuscular mycorrhizal fungi community that colonizes the roots of Uncaria species indicates that these species behave as wild species; therefore, the ex-situ propagation of the species in agricultural systems could be less successful than forest enrichment.

Durum wheat-lentil relay intercropping enhances soil mycorrhizal activity but does not alter structure of arbuscular mycorrhizal fungal community within roots

In intercropping systems, crop species select host-adapted microorganisms and influence the associated plant-microbial interactions like in the case of arbuscular mycorrhizal fungi (AMF). Attempts to assess the impact of intercropping on the activity, diversity, and community composition of AMF remain inconclusive, more so in intercropping systems involving traditional Mediterranean crops such as durum wheat and lentils. We carried out field experiments in Central Italy to assess the impact of relay intercropping durum wheat (Triticum durum Desf. cv. Minosse) and lentil (Lens culinaris Medik. cv. Elsa) on soil mycorrhizal inoculum potential (MIP) (2019 and 2020), AMF root colonization (2019, 2020, and 2021), and root AMF diversity and community composition (2020 and 2021), compared to the respective sole crops. Results showed that relay intercropping enhanced lentil grain yield and durum wheat grain protein concentration but marginally reduced durum wheat grain yield and lentil grain protein concentration. In addition, relay intercropping enhanced soil mycorrhizal activity but differentially influenced mycorrhizal root colonization compared to sole cropping. Sequencing analyses generated a total of 234 amplicon sequence variants belonging to Glomeromycota, which were assigned to 31 virtual taxa using the MaarjAM reference database. Glomeraceae and Claroideoglomeraceae were the most abundant taxa but had contrasting abundances in 2020 and 2021. The overall changes in AMF species diversity and community structure were affected by the interaction between crop species and year, and not by intercropping. Claroideoglomus and Septoglomus showed a strong association with lentil roots while Rhizophagus and Paraglomus were associated with durum wheat roots in 2020, affirming host genotype-AMF preferences. The principal component analysis showed that grain protein concentration was associated with selected mycorrhizal parameters such as community richness and AMF root colonization. Further studies on the functional analysis of the different AMF communities selected by the crop genotype and year may reveal the importance of intercropping in maintaining soil functionality and productivity under low-input systems.

Native mycorrhizal communities in maize roots as affected by plant genotype, starter fertilization and a seed-applied biostimulant

Background and aimsOne of the most promising strategies for sustainable intensification of crop production involves the utilization of beneficial root-associated microorganisms, such as plant growth-promoting bacteria and arbuscular mycorrhizal fungi (AMF). The aim of this study was to investigate whether a seed-applied biostimulant, based on the bacterial strain Bacillus amyloliquefaciens IT-45 and a plant polysaccharide extract, and crop enhancement tools, such as hybrids with contrasting early vigor and nitrogen (N) plus phosphorus (P) starter fertilization, and their interactions, shape the communities of native root-colonizing AMF symbionts in maize.MethodsA factorial growth chamber experiment was set up with two maize genotypes in natural soil. Mycorrhizal colonization was evaluated after root staining. The diversity and composition of AMF communities were assessed by PCR-DGGE of the 18S rRNA gene and amplicon sequencing.ResultsN and P fertilization determined a consistent reduction of AMF root colonization and, in combination of biostimulant, a reduction of AMF richness. The biostimulant alone generally did not affect AMF colonization or the community biodiversity. In addition the effect of the two factors were modulated by maize genotype. In all treatments, predominant AMF were represented by Glomus sp. and Funneliformis mosseae, while populations of the genus Rhizoglomus were rarely detected in biostimulant and NP fertilization treatments.ConclusionThe results of this study increase our understanding of how the biostimulant seed treatment may affect native AMF communities, depending on NP fertilization and maize genotype and may improve the implementation of innovative tools in sustainable and resilient agroecosystems.

Loss of the accessory chromosome converts a pathogenic tree-root fungus into a mutualistic endophyte

Some fungal accessory chromosomes (ACs) may contribute to virulence in plants. However, the mechanisms by which ACs determine specific traits associated with lifestyle transitions along a symbiotic continuum are not clear. Here we delineated the genetic divergence in two sympatric but considerably variable isolates (16B and 16W) of the poplar-associated fungus Stagonosporopsis rhizophilae. We identified a ∼0.6-Mb horizontally acquired AC in 16W that resulted in a mildly parasitic lifestyle in plants. Complete deletion of the AC (Δ16W) significantly altered the fungal phenotype. Specifically, Δ16W was morphologically more similar to 16B, showed enhanced melanization, and established beneficial interactions with poplar plants, thereby acting as a dark septate endophyte. RNA sequencing (RNA-seq) analysis showed that AC loss induced the upregulation of genes related to root colonization and biosynthesis of indole acetic acid and melanin. We observed that the AC maintained a more open status of chromatin across the genome, indicating an impressive remodeling of cis-regulatory elements upon AC loss, which potentially enhanced symbiotic effectiveness. We demonstrated that the symbiotic capacities were non-host-specific through comparable experiments on Triticum– and Arabidopsis–fungus associations. Furthermore, the three isolates generated symbiotic interactions with a nonvascular liverwort. In summary, our study suggests that the AC is a suppressor of symbiosis and provides insights into the underlying mechanisms of mutualism with vascular plants in the absence of traits encoded by the AC. We speculate that AC-situated effectors and other potential secreted molecules may have evolved to specifically target vascular plants and promote mild virulence.

The Fungal Root Endophyte Serendipita indica (Piriformospora indica) Enhances Bread and Durum Wheat Performance under Boron Toxicity at Both Vegetative and Generative Stages of Development through Mechanisms Unrelated to Mineral Homeostasis.

While the importance of beneficial soil microorganisms for soil health and crop performance has been receiving ever-increasing attention, Serendipita indica has been widely studied as a fungal root endophyte with significant potential for increasing the stress tolerance of host plants. Boron (B) toxicity as an adverse soil condition is particularly prevalent in arid and semi-arid regions and threatens crop production. Studies on S. indica-wheat symbiosis are limited, and effects of S. indica on crops have never been reported in the context of B toxicity. Here, two pot experiments were conducted under greenhouse conditions to investigate the effects of S. indica on the growth and yield parameters of bread (Triticum aestivum) and durum wheat (Triticum durum) grown at different levels of B toxicity in native vs. sterilized soil, and parameters related to root colonization, membrane damage, oxidative stress, chlorophyll, and mineral nutrition were measured to elucidate the physiological mechanisms of damage and benefit. Boron toxicity decreased early vegetative growth and grain yield, but it did not affect the straw dry weight of mature plants, whereas S. indica significantly enhanced the vegetative growth, straw dry weight, and the grain number of both wheat species. Membrane damage as demonstrated by increased lipid peroxidation and relative electrolyte leakage was caused by B toxicity and alleviated by S. indica. The benefits provided by S. indica could not be attributed to any significant changes in tissue concentrations of B or other minerals such as phosphorus. Soil sterilization generally improved plant performance but it did not consistently strengthen or weaken the effects of S. indica. The presented results suggest that S. indica may be used as an effective microbial inoculant to enhance wheat growth under adverse soil conditions such as B toxicity through mechanisms that are possibly unrelated to mineral homeostasis.

The Effect of Pre-sowing Treatments with Glomus mosseae and GA3 on the Leaves Physiology of Melia azedarach Seedling

Melia azedarach, a versatile tree belonging to the Meliaceae family, presents a significant challenge in achieving successful seed germination for forest plantations. The robust nature of Melia azedarach seeds necessitates pre-treatments to overcome physical barriers and enhance water absorption. Natural ecosystems often benefit from the symbiotic relationship between Arbuscular mycorrhizal (AM) fungi and plant roots, which promotes survival and growth. This study examined the impact of Glomus mosseae-inoculated soil on Melia azedarach seeds treated with pre-sowing techniques at the Nursery of the Forestry Department, CCSHAU, Hisar in 2019. Glomus mosseae was sown at a rate of 400–500 sporocarps per kg of soil, and its influence was evaluated in terms of physiological parameters, survival rate, root colonization percentage, and sporocarp count. Each replication of the experiment involved 250 seedlings and was repeated five times. Results demonstrated that soils inoculated with Glomus mosseae and treated with gibberellic acid at 200 ppm for 24 hours prior to sowing exhibited significantly higher physiological parameters (chlorophyll and carotenoid content, photosynthesis rate, transpiration rate, and stomatal conductance), survival percentage, root colonization percentage, and sporocarp count (per 100 g of soil). Therefore, the combined use of Glomus mosseae and gibberellic acid at 200 ppm for 24 hours is recommended to enhance physiological growth and plant survival in Melia azedarach.

Enhance of tomato production and induction of changes on the organic profile mediated by Rhizobium biofortification.

The extensive use of chemical fertilizers has served as a response to the increasing need for crop production in recent decades. While it addresses the demand for food, it has resulted in a decline in crop productivity and a heightened negative environmental impact. In contrast, plant probiotic bacteria (PPB) offer a promising alternative to mitigate the negative consequences of chemical fertilizers. PPB can enhance nutrient availability, promote plant growth, and improve nutrient uptake efficiency, thereby reducing the reliance on chemical fertilizers. This study aimed to evaluate the impact of native Rhizobium strains, specifically Rhizobium calliandrae LBP2-1, Rhizobium mayense NSJP1-1, and Rhizobium jaguaris SJP1- 2, on the growth, quality, and rhizobacterial community of tomato crops. Various mechanisms promoting plant growth were investigated, including phosphate solubilization, siderophore production, indole acetic acid synthesis, and cellulose and cellulase production. Additionally, the study involved the assessment of biofilm formation and root colonization by GFP-tagged strains, conducted a microcosm experiment, and analyzed the microbial community using metagenomics of rhizospheric soil. The results showed that the rhizobial strains LBP2-1, NSJP1-1 and SJP1-2 had the ability to solubilize dicalcium phosphate, produce siderophores, synthesize indole acetic acid, cellulose production, biofilm production, and root colonization. Inoculation of tomato plants with native Rhizobium strains influenced growth, fruit quality, and plant microbiome composition. Metagenomic analysis showed increased Proteobacteria abundance and altered alpha diversity indices, indicating changes in rhizospheric bacterial community. Our findings demonstrate the potential that native Rhizobium strains have to be used as a plant probiotic in agricultural crops for the generation of safe food and high nutritional value.

Effects of Altitude and Continuous Cropping on Arbuscular Mycorrhizal Fungi Community in Siraitia grosvenorii Rhizosphere

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.

Growth and yield of rice from mycorrhizal enrichment seedlings on different soil water content

The growth and yield of rice in limited soil water are expected to increase through the application of mycorrhizae due to the increasing root ability to absorb water and nutrients from the soil. The study aimed to determine the role of mycorrhizae on the growth and yield of rice plants in different soil water content. The study was conducted in Mempawah District, West Kalimantan, in February-June 2022. The experiment was arranged in a split-plot randomized complete block design with main plots of mycorrhizae treatment on seedlings (without and with mycorrhizae application), and subplots of soil water content (100%, 80%, 60%). The results showed that mycorrhizae could colonize 60-80% of roots and increase phosphorus absorption at up to 60% of soil water content. Application of mycorrhizae improved plant growth up to 80% of soil water content for the maximum number of a tiller, and 60% of soil water content for the leaf area. Mycorrhizae performed better to increase yield at up to 80% soil water content on the number of productive tillers and grain index of 1,000 seeds, and it performed better at a soil water content of 100% for grain weight per hill.
 Keywords: microorganisms, plant resistance, rice production, root colonization

Phytomanagement of Zn- and Cd-Contaminated Soil: Helianthus annuus Biomass Production and Metal Remediation Abilities with Plant-Growth-Promoting Microbiota Assistance

Mining and industrial activity are contributing to the increase in heavy metal (HM) pollution in soils. Phytoremediation coupled to selected rhizosphere microbiota is an environmentally friendly technology designed to promote HM bioremediation in soils. In this study, sunflower (Helianthus annuus L.) was used together with Rhizophagus irregularis, an arbuscular mycorrhizal fungi (AMF), and Cupriavidus sp. strain 1C2, a plant growth promoting rhizobacteria (PGPR), as a phytoremediation strategy to remove Zn and Cd from an industrial soil (599 mg Zn kg−1 and 1.2 mg Cd kg−1). The work aimed to understand if it is possible to gradually remediate the tested soil while simultaneously obtaining significant yields of biomass with further energetic values by comparison to the conventional growth of the plant in agricultural (non-contaminated) soil. The H. annuus biomass harvested in the contaminated industrial soil was 17% lower than that grown in the agricultural soil—corresponding to yields of 19, 620, 199 and 52 g m−2 of roots, stems, flowers and seeds. It was possible to remove ca. 0.04 and 0.91% of the Zn and Cd of the industrial soil, respectively, via the HM accumulation on the biomass produced. The survival of applied microbiota was indicated by a high root colonization rate of AMF (about 50% more than in non-inoculated agricultural soil) and identification of strain 1C2 in the rhizosphere at the end of the phytoremediation assay. In this study, a phytoremediation strategy encompassing the application of an energetic crop inoculated with known beneficial microbiota applied to a real contaminated soil was successfully tested, with the production of plant biomass with the potential for upstream energetic valorisation purposes.

Root architecture, root biomass and nutrient cycling in a mixed‐species agroforestry system

AbstractUnderstanding root development in soil profiles of agroforestry systems is challenging. It is uncertain to what extent the proximity of cash crops, such as cocoa and coffee, to shade trees reduces nutrient concentrations in the topsoil and whether the cash crops continue to develop fine roots in the topsoil when they are planted in close proximity to shade trees. We aimed to investigate micro‐ and macro‐nutrient concentrations in the soil profile and understand root architecture using a novel DNA metabarcoding approach in an agroforestry system where cocoa and coffee were interplanted with a shade tree, canarium. Soil and root samples were collected from (1) cocoa‐only, (2) cocoa‐canarium, (3) canarium‐only positions in a cocoa plantation, (4) coffee‐only, (5) coffee‐canarium and (6) canarium‐only positions in a coffee plantation. Proximity of shade trees did not limit nutrient concentrations for cash crops. Topsoil concentrations of total N (TN: 0.59% and 0.69%), phosphorus (P: 7.28 and 6.65 mg/kg), potassium (K: 360 and 755 mg/kg) and calcium (Ca: 1865 and 1044 mg/kg) under cocoa and coffee trees, respectively, did not differ significantly from those under the corresponding canarium trees. Soil TN, K and Ca concentrations were well above minimum required concentrations under both cocoa and coffee. DNA metabarcoding showed that canarium trees occupied deeper rooting zones (30–80 cm soil depth) than cocoa and coffee trees (0–30 cm soil depth). DNA metabarcoding demonstrated greater root colonisation of the topsoil by cocoa and coffee than canarium, suggesting that canarium had the potential to extract nutrients from deeper soil layers. Soil Ca concentrations were associated with cocoa root biomass whereas soil NO3−‐N concentrations were associated with coffee root biomass. Our study highlighted the value of selecting suitable shade trees that maintain soil nutrient concentrations for cash crops. Furthermore, DNA metabarcoding can facilitate root distribution studies in complex agroforestry systems, thus providing insights into appropriate tree‐planting designs.