Endophytic fungus improves peanut drought resistance by reassembling the root-dwelling community of arbuscular mycorrhizal fungi

Fungal endophyte promotes plant growth and disease resistance of Arachis hypogaea L. by reshaping the core root microbiome under monocropping conditions

Fungal endophytes play critical roles in helping plants adapt to adverse environmental conditions. The root endophyte Phomopsis liquidambaris can promote the growth and disease control of peanut plants grown under monocropping systems; however, how such beneficial traits are produced is largely unknown. Since the plant endophytic microbiome is directly linked to plant growth and health, and the composition of which has been found to be potentially influenced by microbial inoculants, this study aims to clarify the roles of root endophytic bacterial communities in P. liquidambaris-mediated plant fitness enhancement under monocropping conditions. Here, we found that P. liquidambaris inoculation induced significant changes in the root bacterial community: enriching some beneficial bacteria such as Bradyrhizobium sp. and Streptomyces sp. in the roots, and improving the core microbial-based interaction network. Next, we assembled and simplified a synthetic community (SynII) based on P. liquidambaris-derived key taxa, including Bacillus sp. HB1, Bacillus sp. HB9, Burkholderia sp. MB7, Pseudomonas sp. MB2, Streptomyces sp. MB6, and Bradyrhizobium sp. MB15. Furthermore, the application of the simplified synthetic community suppressed root rot caused by Fusarium oxysporum, promoted plant growth, and increased peanut yields under continuous monocropping conditions. The resistance of synII to F. oxysporum is related to the increased activity of defense enzymes. In addition, synII application significantly increased shoot and root biomass, and yield by 35.56%, 81.19%, and 34.31%, respectively. Collectively, our results suggest that the reshaping of root core microbiota plays an important role in the probiotic-mediated adaptability of plants under adverse environments.

Accumulation of Health-Promoting Compounds in Upland Black Rice by Interacting Mycorrhizal and Endophytic Fungi

There is an increasing interest in finding eco-friendly and safe approaches to increase agricultural productivity and deliver healthy foods. Arbuscular mycorrhizal fungi (AMF) and endophytic fungi (EPF) are important components of sustainable agriculture in view of their ability to increase productivity and various plant secondary metabolites with health-promoting effects. In a pot experiment, our main research question was to evaluate the additive and synergistic effects of an AMF and four root-endophytic fungi on plant performance and on the accumulation of health-promoting secondary compounds. Plant growth varied between the treatments with both single inoculants and co-inoculation of an AMF and four EPF strains. We found that inoculation with a single EPF positively affected the growth and biomass production of most of the plant-endophyte consortia examined. The introduction of AMF into this experiment (dual inoculation) had a beneficial effect on plant growth and yield. AMF, Rhizophagus variabilis KS-02 co-inoculated with EPF, Trichoderma zelobreve PBMP16 increased the highest biomass, exceeding the growth rate of non-inoculated plants. Co-inoculated R. variabilis KS-02 and T. zelobreve PBMP16 had significantly greater beneficial effects on almost all aspects of plant growth, photosynthesis-related parameters, and yield. It also promoted root growth quality and plant nutrient uptake. The phenolic compounds, anthocyanin, and antioxidant capacity in rice seeds harvested from plants co-inoculated with AMF and EPF were dramatically increased compared with those from non-inoculated plants. In conclusion, our results indicated that EPF and AMF contributed to symbiosis in Maled Phai cultivar and were coordinately involved in promoting plant growth performance under a pot trial.

Drought Tolerance of Legumes: Physiology and the Role of the Microbiome

Water scarcity and global warming make drought-tolerant plant species more in-demand than ever. The most drastic damage exerted by drought occurs during the critical growth stages of seed development and reproduction. In the course of their evolution, plants form a variety of drought-tolerance mechanisms, including recruiting beneficial microorganisms. Legumes (one of the three largest groups of higher plants) have unique features and the potential to adapt to abiotic stress. The available literature discusses the genetic (breeding) and physiological aspects of drought tolerance in legumes, neglecting the role of the microbiome. Our review aims to fill this gap: starting with the physiological mechanisms of legume drought adaptation, we describe the symbiotic relationship of the plant host with the microbial community and its role in facing drought. We consider two types of studies related to microbiomes in low-water conditions: comparisons and microbiome engineering (modulation). The first type of research includes diversity shifts and the isolation of microorganisms from the various plant niches to which they belong. The second type focuses on manipulating the plant holobiont through microbiome engineering-a promising biotech strategy to improve the yield and stress-resistance of legumes.

Epichloë Fungal Endophytes Have More Host-Dependent Effects on the Soil Microenvironment than on the Initial Litter Quality

Fungal endophytes have been extensively found in most terrestrial plants. This type of plant–microorganism symbiosis generates many benefits for plant growth by promoting nutrient availability, uptake, and resistance to environmental disease or stress. Recent studies have reported that fungal endophytes have a potential impact on plant litter decomposition, but the mechanisms behind its effect are not well understood. We proposed a hypothesis that the impacts of fungal endophytes on litter decomposition are not only due to a shift in the symbiont-induced litter quality but a shift in soil microenvironment. To test this hypothesis, we set-up a field trial by planting three locally dominant grass species (wild barley, drunken horse grass, and perennial ryegrass) with Epichloë endophyte-infected (E+) and -free (E-) status, respectively. The aboveground litter and bulk soil from each plant species were collected. The litter quality and the soil biotic and abiotic parameters were analyzed to identify their changes across E+ and E- status and plant species. While Epichloë endophyte status mainly caused a significant shift in soil microenvironment, plant species had a dominant effect on litter quality. Available nitrogen (N) and phosphorus (P) as well as soil organic carbon and microbial biomass in most soils with planting E+ plants increased by 17.19%, 14.28%, 23.82%, and 11.54%, respectively, in comparison to soils with planting E- plants. Our results confirm that fungal endophytes have more of an influence on the soil microenvironment than the aboveground litter quality, providing a partial explanation of the home-field advantage of litter decomposition.

Different Arbuscular Mycorrhizal Fungi Established by Two Inoculation Methods Improve Growth and Drought Resistance of Cinnamomum Migao Seedlings Differently

Simple Summary

Drought is a global climatic phenomenon and one of the main factors that negatively affect plant growth. Karst is a unique type of ecosystem where ecological degradation is becoming more and more serious due to the aggravation of global drought. Vegetation restoration is an effective method for preventing ecological degradation in Karst ecosystems. Cinnamomum migao is selected as the tree species for vegetation restoration, because it is a unique, fast-growing medicinal plant of Southwest China that only thrives in Karst regions. Arbuscular mycorrhizal fungi (AMF) are an important component of the soil biota in ecosystems and alleviate drought stress in plants by forming a mutualistic symbiosis. Most previous studies just considered the effects of AMF species on drought resistance but did not evaluate different inoculation methods. The aim of the present study was to compare the effects of different AMF resulting from the use of different inoculation methods on the growth and drought resistance of C. migao seedlings in Karst soil. The findings of this study will improve the success rate of reforestation programs in Karst ecosystems through the utilization of these important microorganisms.

Abstract

Drought stress is one of the greatest obstacles affecting field crop productivity in arid and semi-arid regions, and its severity and frequency are expected to increase due to human-induced changes to the environment and climate. Drought has led to rocky desertification in Karst regions. Cinnamomum migao is a unique, fast-growing medicinal plant of Southwest China that only thrives in Karst regions. Arbuscular mycorrhizal fungi (AMF) symbiosis alleviates drought stress in plants; however, establishment and function of the symbiotic interaction between AMF host plant in relation to the inoculation method remain unclear. Therefore, we conducted an experiment to investigate the effects of AMF species (Glomus etunicatum and Funneliformis mosseae) and two inoculation methods (seed vs. seedling inoculation) under drought stress on C. migao seedlings, and quantified mycorrhizal colonization, AMF spore density, root vigor, relative water content, C. migao growth, antioxidant enzyme activities, and osmotic adjustment. Inoculation with AMF (G. etunicatum and F. mosseae) positively affected the growth and root vigor of Cinnamomum migao under drought stress, regardless of the inoculation method. Additionally, both AMF species markedly upregulated antioxidant enzyme activities and osmotic adjustment substances, regardless of the inoculation method. Our results showed that the collective stimulatory effect of G. etunicatum is more efficient than that of F. mosseae. AMF application could promote afforestation with C. migao to prevent rocky desertification in Karst regions where water is the greatest limiting factor on plant growth and yield.

Dual inoculation of dark septate endophytes and Trichoderma viride drives plant performance and rhizosphere microbiome adaptations of Astragalus mongholicus to drought

Rhizosphere microbiome adapts their structural compositions to water scarcity and have the potential to mitigate drought stress of plants. To unlock this potential, it is crucial to understand community responses to drought in the interplay between soil properties, water management and exogenous microbes interference. Inoculation with dark septate endophytes (DSE) (Acrocalymma vagum, Paraboeremia putaminum) and Trichoderma viride on Astragalus mongholicus grown in the non‐sterile soil was exposed to drought. Rhizosphere microbiome were assessed by Illumina MiSeq sequencing of the 16S and ITS2 rRNA genes. Inoculation positively affected plant growth depending on DSE species and water regime. Ascomycota, Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes were the dominant phyla. The effects of dual inoculation on bacterial community were greater than those on fungal community, and combination of P. putaminum and T. viride exerted a stronger impact on the microbiome under drought stress. The observed changes in soil factors caused by inoculation could be explained by the variations in microbiome composition. Rhizosphere microbiome mediated by inoculation exhibited distinct preferences for various growth parameters. These findings suggest that dual inoculation of DSE and T. viride enriched beneficial microbiota, altered soil nutrient status and might contribute to enhance the cultivation of medicinal plants in dryland agriculture.

Co-Inoculation of an Endophytic and Arbuscular Mycorrhizal Fungus Improve Growth and Yield of Helianthus tuberosus L. under Field Condition

Endophytic fungi (EPF) and arbuscular mycorrhizal fungi (AMF) symbioses can promote the growth and productivity of several types of plants. This work aimed to investigate the effect of co-inoculation of an EPF Exserohilum rostratum NMS1.5 and an AMF Glomus etunicatum UDCN52867 g.5 on the growth and yields of sunchoke (Helianthus tuberosus L.) compared to the effects of full-dose and half-dose chemical fertilizer (15-15-15) under field conditions. Several plant growth parameters of the co-inoculated plants were significantly higher than the other treatments. Remarkably, such an effect was relatively equal to that of the full-dose chemical fertilizers. Moreover, the co-inoculation of EPF and AMF significantly improved the tuber yield production, even better than the use of a chemical fertilizer. This is the first report to show that plant growth promoting effects of the co-inoculation of EPF and AMF were exceptionally greater than those of the chemical fertilizer. Therefore, our EPF and AMF could potentially be used as a biofertilizer for promoting the growth and yield of sunchoke in the fields.

Soil legacy of arbuscular mycorrhizal fungus Gigaspora margarita: The potassium-sequestering glomalin improves peanut (Arachis hypogaea) drought resistance and pod yield

In agroecosystems, drought stress severely threatens crops development. Although potassium (K) is required in amounts by crops under drought stress, the mobilization and availablity of K are limited by the soil water status. Arbuscular mycorrhizal (AM) fungi can form mutualistic associations with most crops and play direct or indirect roles in the host drought resistance. Considering that the glomalin generated by living AM fungal hyphae can sequester multiple minerals, however, the function of mineral-sequestering glomalin in the crop drought resistance remains unclear. In this study, peanuts cultivated in the sterilized soil with a history of AM fungi inoculation showed significantly enhanced leaf K accumulation, drought resistance and pod yield under drought stress. Through the collection of different types of mineral-sequestering glomalin from living AM fungal hyphae, the peanut drought resistance was improved only when K-sequestering glomalin was added. Moreover, we found that peanut root exudates could prime the dissociation of glomalin-bound K and further satisfy the K requirement of crops. Our study is the first report that K-sequestering glomalin could improve drought performance and peanut pod yield, and it helps us to understand the ecological importance of improving AM symbiosis to face agricultural challenges.