Rhizosphere最新文献

Eroded agricultural soils have reduced soil organic carbon (SOC) levels that may affect the plant-microbiome interactions in the rhizosphere. We explored the impact of simulated erosion on major microbial groups in a pot experiment with rapeseed (Brassica napus L.) grown on arable soil with the potential to capture SOC. An erosion gradient was simulated by admixture (0%, 12%, 24%) of subsoil horizon (Bt) to topsoil (Ap) material. Rapeseed plants were pulse-labeled with ¹⁴CO₂ at three growth stages and two soil compartments (bulk and rhizosphere soil) were sampled. Fungal ITS copy numbers were consistently higher in the rhizosphere and decreased with progressing plant growth stages. A significant increase of bacterial 16S rRNA gene copies in the rhizosphere only occurred at flowering. A response of fungal abundance to subsoil admixture was found detectable based on fungi:Bacteria and fungi:Archaea ratio at flowering. Archaea were neither affected by soil compartment nor subsoil admixture. ¹⁴C activity of microbial biomass, an indicator for relative input of freshly assimilated C into soil microbiome, was impacted by growth stage and compartment and decreased with ongoing growth stage. During the rosette growth stage, the ¹⁴C activity of the microbial biomass was elevated in the rhizosphere of the eroded soil indicating a plant response to the erosion factor. Our experiment revealed a compositional separation of the fungal community along the simulated erosion gradient and a selection of fungi for the two different soil compartments at flowering. Olpidimycetes, Fusarium and Rhizopus and putative pathogens were enriched in the rhizosphere at flowering. Fungi may have a competitive advantage in the rhizosphere of strongly eroded and nutrient diluted soils due to ecological adaptation and morphological traits i.e. hyphae that can bypass soil areas with low nutrient availability.

Arbuscular mycorrhizal fungi (AMF) have been demonstrated to influence the bioavailability of heavy metals (HM) in the rhizosphere and their absorption by plants. Nitric oxide (NO) has been shown to increase plant tolerance to environmental stresses and promote the plant-fungal symbiotic relationship. However, to date, no research has been conducted to investigate the impact of utilizing living organisms with specific molecules that are effective in promoting plant growth in conjunction with the chemical alterations of HM in the rhizosphere. Therefore, this study was conducted as a completely randomized factorial design using the rhizobox technique to investigate whether the use of Funneliformis mosseae fungi and sodium nitroprusside (SNP, 100 mM) as a donor of NO, alone or in combination, can improve corn plant growth and affect the Cd fractions in the rhizosphere of Cd-contaminated soil. The results show that the inoculation of AMF and the application of SNP, either alone or in combination, significantly increased plant growth. This was achieved by reducing the bioavailable form of Cd in the rhizosphere, which in turn led to a decrease in the concentration of Cd in corn plant tissues. The inoculation of AMF, either alone or in combination with SNP, resulted in a decrease in the concentration of Cd in its exchangeable (EXCH), carbonate-bound (CAR), and Fe–Mn oxides-bound (MnOX and FeOX) forms, and an increase in its organic matter-bound (ORG) and residual (RES) forms in the rhizosphere. The study found that the rhizosphere had lower concentration of bioavailable form of Cd (EXCH-Cd (43%), CAR-Cd (9%), MnOX-CD (18%), FeOX-Cd (33%) and ORG-Cd (30%)) and higher concentration of low-toxic form of Cd (RES-Cd (56%)). This indicates the role of root exudates in the redistribution of Cd fractions in soil. The study also revealed that AMF colonization, in combination with SNP, affected the biogeochemical fractions of Cd and reduced Cd mobility in the rhizosphere. This improvement in Cd mobility led to reduced Cd accumulation in the plant tissues, resulting in improved corn plant growth.

Root length, as one of the most common characteristics of root, has an important role in controlling concentrated flow erosion. This study has explored the overall trends in reducing soil detachment rate as a function of the root length, based on the Hill curve model. In order to study the mechanical effects of root length on concentrated flow erosion rates, hydromulch was sprayed on soil surface and soil detachment rate was measured using a hydraulic flume. We found a nonlinear model for soil detachment rate as a function of root length (R² = 0.81). Moreover, soil detachment rate was estimated well by the nonlinear models for ranges of flow shear stress (from 5.28 to 15.90 Pa) (p < 0.01) with R² > 0.75. These results can be used to predict the soil erosion resistance to overland flow using root length characteristic.

Mikania micrantha (M. micrantha), a plant species native to Central and South America, is one of the 100 most destructive invasive species. Its rapid growth and superior competitiveness compared to other plants cause significant damage to the natural ecosystem and result in substantial economic losses. Soil plays a crucial role as a medium for plants to obtain nutrients and to exchange substances with the environment. The presence of soil microorganisms is essential for plant survival and growth. Therefore, numerous studies have been carried out to investigate the changes in soil microbial structure and soil physical and chemical properties following M. micrantha invasion. Here, we reviewed recent research on soil microorganisms of M. micrantha from three perspectives: microbial diversity, abundance, and function. We summarized that the invasion of M. micrantha leads to an increase in microbial diversity, which ultimately benefits the plant growth. Furthermore, the changes in soil nutrients contribute to an increase in the density and abundance of the microbial population. This leads to an enrichment of biological control bacteria, which helps to suppress pathogenic bacteria in the rhizosphere of M. micrantha. Additionally, the soil associated with M. micrantha has a higher diversity and abundance of nitrogen-fixing bacteria, ammonifiers, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, and other microorganisms. As a result, the efficiency of nitrogen fixation and ammonification are improved. This review not only provide valuable insights into the soil microorganisms associated with M. micrantha but also offer future research directions and the applicability of the knowledge gained.

Secondary metabolite production in medicinal plants and other plants is improved by arbuscular mycorrhizae, plant stress, as well as nutritional factors. The compounds responsible for Sun Protection Factor from Anadenanthera colubrina (Vell.) such as flavonoids and proanthocyanidins may also increase by manipulation of plant stress or nutrient status, and inoculation with arbuscular mycorrhizal fungi (AMF). However, specific gaps regarding the viability of this agricultural tool need clarification, especially regarding the role of Phosphorus (P), one of the mycorrhizal symbiosis regulators and widely employed in plant cultivation. Therefore, this study aimed to understand the role of P in regulating SPF in Anadenanthera colubrina when cultivated in association with arbuscular mycorrhizal fungi (AMF). To this end, two concentrations of P₂O₅ (8 mg dm⁻³ and 50 mg dm⁻³) were evaluated, and two inoculation treatments were tested: control and seedlings inoculated with AMF inoculant. After 150 days in a greenhouse, the leaves were collected to obtain the ethanolic extracts and used to assess the SPF, production of flavonols, proanthocyanidins, saponins, pigments, and in vitro antioxidant activity. The presence of higher P levels in the soil (50 mg dm⁻³) renders mycorrhizal inoculation dispensable for the enhancement of SPF, production of photoprotective compounds, and antioxidant activity as plants grown under this condition showed a six-fold increase compared to non-inoculated seedlings kept in soil with a lower P level. On the other hand, leaves of A. colubrina seedlings inoculated with AMF and cultivated in soil supplemented with 8 mg P dm⁻³ displayed a SPF with a 4.9-fold increase and the biosynthesis of photoprotective and antioxidant compounds enhanced by more than five-fold compared to those not inoculated. Despite these benefits, these cultivation practices did not increase the accumulation of carotenoids and chlorophylls. Mycorrhizal inoculation and phosphate fertilization are agricultural practices that, independently, contribute to the increased SPF, biosynthesis of secondary metabolites, and antioxidant activity in A. colubrina leaves.

Acaulospora is one of the dominant genera of AMF associated with waterlogged vegetation, and its dominance was also revealed in the roots of a lowland rice variety indigenous to Southern Thailand. In a preliminary finding, the isolated Acaulospora showed growth suppression of lowland japonica Nipponbare rice, even in high phosphorus (P) soil. The isolated Acaulospora was identified to species level and assigned as Acaulospora cf. morrowiae Phattalung 1. The mycorrhizal growth response (MGR) of an upland indica rice and maize to A. cf. morrowiae was further tested under low and high P conditions. AMF colonization rates were high, over 70%, in both cases, with perfect arbuscule and vesicle formation; however, growth depression of the host plants was markedly observed. Reduced nutrient accumulation in both shoots and roots of host plants was noted, as depicted by nutrient profiling. To further substantiate the negative MGR to inoculation of A. cf. morrowiae, a standardized in vivo bioassay was performed using maize seedlings in a sand and perlite mixture, ensuring low P with 20 mg kg⁻¹ P in the form of insoluble CaH₂PO₄. Shoot and root growth of maize seedlings were reduced at 23.7 and 36.1%, respectively, by the inoculation of AMF. The nutrient-parasitic nature of this AMF results from unproportioned drainage of photosynthates, indicating an unbalanced primary/nutrient trade-off system between symbionts. The overall associative merits or demerits of A. cf. morrowiae cannot be ruled out without thorough investigations considering several ecological perspectives and its fitter survival and dominance in waterlogged soils.

Bioaugmentation of microbial strains could act as sustainable intervention in soil for enhancing the availability of nutrients. Zinc deficiency is widely reported across the world and application of zinc based fertilizers mostly resulted in formation of unavailable zinc in soil. A fungus with zinc solubilisation was isolated from rice and identified as Phanerochaete concrescens KS7. Inoculation of fungus in culture medium resulted in decrease of pH to 4.4 and analysis of medium revealed higher content of citric and gluconic acid in comparison with uninoculated broth. Indole acetic acid production by the strain was found to be enhanced in presence of tryptophan under broth conditions. Zinc solubilisation potential of strain was quantified in medium amended with insoluble zinc source. There was enhanced root growth and significantly higher zinc concentration in rice seedling on inoculation with KS7. There was increase in plant height, leaf area, number of grains per panicle and grain yield per plant on inoculation with P. concrescens in two selected varieties of rice grown in zinc deficient soil. Partition analysis was done for zinc in root, stem and grains and there was significant increase of zinc content in rice grain on inoculation with KS7. Total and available zinc was quantified from soil after harvest of rice and found that zinc contents were higher in soil of KS7 inoculated plants. Phanerochaete concrescens KS7 could act as potential solubilizer of zinc in soil and improve the zinc content of crop produce especially in zinc deficient soils.

Abiotic stress, such as high temperatures, droughts and soil salinity, as well as biotic stress, such as pythopathogenic bacteria, are causing serious damage to crops and they result in significant economic losses. In addition, excessive application of agrochemicals has deteriorated productive agricultural land, contributed to spreading antimicrobial resistance genes among pathogenic microorganisms and caused damage to human health. Developing alternative strategies to the use of chemicals is an ongoing challenge for achieving a sustainable agriculture. In this context, biological products, including bacteriocins, enhance crop growth and health without harming the environment. Bacteriocins are proteinaceous compounds that exhibit high specificity and kill competitors closely related to the producing bacteria. They are secreted by both Gram-negative bacteria and Gram-positive bacteria, and they have been used to treat bacterial infections in humans and animals, and to preserve food. In recent years, studies that projected the use of bacteriocins in agriculture have increased due to their high biotechnological potential. These bacteriocins have been explored as plant biostimulants or as biocontrol agents, and provide an innovative solution to the problems in agriculture. In particular, tailocins have a great potential as antimicrobials because they are very stable, extremely specific, and efficient as killers; in fact, a single particle is enough to kill a susceptible cell.In this review, we examine the bacteriocins produced by rhizobacteria and their application for a sustainable agriculture, a topic that has not been addressed extensively yet. In addition, we discuss bacteriocin expression in plants and the study of bacteriocins through omics.

Kiwifruit vine decline syndrome (KVDS), which is responsible for a progressive decline in yields in Italy, is linked to a non-specific reduction in root development, the biotic or abiotic causes of which are still unclear. Dactylonectria is one of the most common soil-borne fungi associated with kiwifruit vines, However, its role in KVDS has not yet been clarified; therefore, Dactylonectria functional relationship with kiwifruit vine at rhizosphere level was investigated focusing solely on its exudates. Six isolates, four from kiwifruit-bearing soils belonging to D. torresensis. D. ecuadoriensis, D. novozelandica and D. pauciseptata, and two D. torresensis from a virgin soil, was tested for phytotoxicity of exudates by growing kiwifruit in vitro plants on MS media amended at 50% with sterile fungal filtrates. Parallelly, low molecular weight (LMW) metabolic profile of fungal filtrates was evaluated with untargeted metabolomics approach using LC-MS/TOF. The fungal isolates from kiwifruit bearing soil were much richer in LMW metabolites than those from virgin soil. Non host specific mycotoxins such as Aflaxoxin B2, Alternariol and Alterlactone were found in these isolates along with a number of metabolites most of which were characterised by antimicrobial properties. D. torresensis isolates were clearly discriminated from the other three species based on metabolic profile. A negative Pearson correlation between the growth index of kiwifruit vitro-plants and LMW metabolite count per isolate (richness) showed that the latter were associated with phytotoxicity, but the degree of correlation (r = −0.639) indicated that they were not the only component responsible. The results suggest that kiwifruit vines may alter the composition of the Dactylonectria spp. community in the root zone, which in turn may directly or indirectly contribute to kiwifruit vine decline syndrome.