Arbuscular Mycorrhizal Root Colonization Research Articles

Plant genotype and inoculation with indigenous arbuscular mycorrhizal (AM) fungi modulate wheat productivity and quality of processed products through changes in the frequency of root AM fungal taxa

ContextArbuscular mycorrhizal fungi (AMF) have been extensively applied as biofertilizers in wheat to promote crop productivity. However, variability in AM root colonization, grain yield, and nutrients was observed among wheat genotypes and according to AM genotype and environment. ObjectivesWe hypothesized that wheat response to AM inoculation is more affected by genotype than environment; the response is driven by increases in AM abundance and community structure changes, and not by modification of composition. MethodsWe inoculated an indigenous AM consortium on four old genotypes (Bianco Nostrale, Andriolo, Abbondanza, Sieve) and one modern variety (Bologna) of bread wheat for two years. The effect was evaluated by assessing grain yield, nutrients, and quality of processed products (flour and breadsticks), while the AM abundance and the community composition and structure in roots were characterized, at two plant growth stages, using morphological and molecular tools. ResultsThe functional traits of AMF and plant were better explained by inoculation than by genotype or environment (33 %, 17 %, 4 % of total explained variance), although significant interactions environment x genotype and genotype x inoculation were highlighted. Consistent increases in AM abundance in Sieve and Bologna were associated with positive changes in grain yield and nutrients, supporting the good responsiveness of these genotypes with inoculated AMF, while the plant response of other genotypes was shaped by air temperature and rainfall. However, we did not find significant correlations between changes in AM colonization and mycorrhizal response ratio, with the exception of P and K. After inoculation, AM community composition was similar in all wheat genotypes, but the structure greatly differed among genotypes in interaction with inoculation and plant growth stage. These changes were significantly related to wheat productivity. A Septoglomus taxon, present in the inoculum, was the best predictor of wheat performance. The characterization of the community structure at early crop development and maturity allowed the identification of fast and latest active AM colonizers. Our results showed for the first time that AM inoculation affect the rheological parameters and nutraceuticals of processed products, although the response was modulated by genotype. ConclusionsThe selection of responsive wheat genotypes is fundamental for the positive outcome of inoculation. The positive effects on wheat productivity and field persistence of the inoculated AMF support the use of indigenous consortia that have low impacts on resident AMF. SignificanceOur findings advance the understanding of the facilitative mechanisms that underlie compatibility between AMF and wheat genotypes.

Effect of Cinnamon Leaf Compost on Selected Soil Properties in Cinnamon (Cinnamomum zeylanicum Blume) Growing Soils

Integrated nutrient-management programs incorporating organic and inorganic fertilizers have been suggested to increase crop yields and reduce adverse environmental impacts in intensive agriculture. This study was conducted to investigate the effect of long-term cinnamon leaf compost (CLC) application on some selected physical, biological and chemical soil properties and the horizontal and vertical distribution of some selected soil properties in cinnamon-growing soils. The study was conducted in the National Cinnamon Research and Training Center, Palolpitiya, from January to April 2022. The experimental design was Randomized Complete Block Design (RCBD) with six treatments (T1-Control, T2-Current recommendation (CR), T3-3/4 CR with 5 t/ha/yr CLC, T4-1/2 CR with 10 t/ha/yr CLC, T5-1/4 CR with 15 t/ha/yr CLC, T6-20 t/ha/yr CLC) and three replicates. Soil samples were collected considering three horizontal distances (15, 30 and 45 cm) and with three depths (10, 20 and 30 cm). Soil physical properties (aggregate stability, bulk density, soil moisture), chemical properties (soil organic carbon (SOC), pH, electrical conductivity (EC)), and biological properties (arbuscular mycorrhizal root colonization) were determined. Water stable aggregate (WSA), SOC, and soil pH were significantly affected by the treatments, and all the variables except EC were significantly affected by the soil depth (p<0.05). Soil pH was the only variable that was significantly affected by the horizontal distance (p<0.05). Only SOC and pH have shown a significant interaction effect among treatments and depth. The application of CLC (20 t/ha/yr) significantly increases the WSA and SOC. Arbuscular mycorrhizal fungi root colonization was increased with the incorporation of CLC. Continuous application of inorganic fertilizers (T2) caused soil compaction and acidification. WSA, soil pH, and SOC were significantly improved within the 0-10 cm soil depth. The best performances of WSA, pH, and EC were shown in 30-45 cm and SOC in 15–30 cm horizontal distance from the plant base and 0-10 cm soil depth with the application of 1/2 CR and 10 t/ha/yr CLC comparison to other fertilizer combinations. 
 Keywords: Aggregates, Mycorrhizae, pH, Soil organic carbon

Attenuation of Zucchini mosaic virus disease in cucumber plants by mycorrhizal symbiosis

Key messageArbuscular mycorrhizal fungi generated systemic acquired resistance in cucumber to Zucchini yellow mosaic virus, indicating their prospective application in the soil as a sustainable, environmentally friendly approach to inhibit the spread of pathogens.The wide spread of plant pathogens affects the whole world, causing several plant diseases and threatening national food security as it disrupts the quantity and quality of economically important crops. Recently, environmentally acceptable mitigating practices have been required for sustainable agriculture, restricting the use of chemical fertilizers in agricultural areas. Herein, the biological control of Zucchini yellow mosaic virus (ZYMV) in cucumber (Cucumis sativus L.) plants using arbuscular mycorrhizal (AM) fungi was investigated. Compared to control plants, ZYMV-infected plants displayed high disease incidence (DI) and severity (DS) with various symptoms, including severe yellow mosaic, mottling and green blisters of leaves. However, AM fungal inoculation exhibited 50% inhibition for these symptoms and limited DS to 26% as compared to non-colonized ones. The detection of ZYMV by the Enzyme-Linked Immunosorbent Assay technique exhibited a significant reduction in AM-inoculated plants (5.23-fold) compared with non-colonized ones. Besides, mycorrhizal root colonization (F%) was slightly reduced by ZYMV infection. ZYMV infection decreased all growth parameters and pigment fractions and increased the malondialdehyde (MDA) content, however, these parameters were significantly enhanced and the MDA content was decreased by AM fungal colonization. Also, the protein, proline and antioxidant enzymes (POX and CAT) were increased with ZYMV infection with more enhancements due to AM root colonization. Remarkably, defence pathogenesis-related (PR) genes such as PR-a, PR-b, and PR-10 were quickly expressed in response to AM treatment. Our findings demonstrated the beneficial function of AM fungi in triggering the plant defence against ZYMV as they caused systemic acquired resistance in cucumber plants and supported their potential use in the soil as an environment-friendly method of hindering the spread of pathogenic microorganisms sustainably.

The Role of CLE Peptides in the Suppression of Mycorrhizal Colonization of Tomato.

Symbioses with beneficial microbes are widespread in plants, but these relationships must balance the energy invested by the plants with the nutrients acquired. Symbiosis with arbuscular mycorrhizal (AM) fungi occurs throughout land plants, but our understanding of the genes and signals that regulate colonization levels is limited, especially in non-legumes. Here, we demonstrate that in tomato, two CLV3/EMBRYO-SURROUNDING REGION (CLE) peptides, SlCLE10 and SlCLE11, act to suppress AM colonization of roots. Mutant studies and overexpression via hairy transformation indicate that SlCLE11 acts locally in the root to limit AM colonization. Indeed, SlCLE11 expression is strongly induced in AM-colonized roots, but SlCLE11 is not required for phosphate suppression of AM colonization. SlCLE11 requires the FIN gene that encodes an enzyme required for CLE peptide arabinosylation to suppress mycorrhizal colonization. However, SlCLE11 suppression of AM does not require two CLE receptors with roles in regulating AM colonization, SlFAB (CLAVATA1 ortholog) or SlCLV2. Indeed, multiple parallel pathways appear to suppress mycorrhizal colonization in tomato, as double mutant studies indicate that SlCLV2 and FIN have an additive influence on mycorrhizal colonization. SlCLE10 appears to play a more minor or redundant role, as cle10 mutants did not influence intraradical AM colonization. However, the fact that cle10 mutants had an elevated number of hyphopodia and that ectopic overexpression of SlCLE10 did suppress mycorrhizal colonization suggests that SlCLE10 may also play a role in suppressing AM colonization. Our findings show that CLE peptides regulate AM colonization in tomato and at least SlCLE11 likely requires arabinosylation for activity.

Fine-resolution global maps of root biomass carbon colonized by arbuscular and ectomycorrhizal fungi

Despite the recognized importance of mycorrhizal associations in ecosystem functioning, the actual abundance patterns of mycorrhizal fungi belowground are still unknown. This information is key for better quantification of mycorrhizal impacts on ecosystem processes and for incorporating mycorrhizal pathways into global biogeochemical models. Here we present the first high-resolution maps of fine root stocks colonized by arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) fungi (MgC ha−1). The maps were assembled by combining multiple open-source databases holding information on root biomass carbon, the proportion of AM and EcM tree biomass, plot-level relative abundance of plant species and intensity of AM and EcM root colonization. We calculated root-associated AM and EcM abundance in 881 spatial units, defined as the combination of ecoregions and land cover types across six continents. The highest AM abundances are observed in the (sub-)tropics, while the highest EcM abundances occur in the taiga regions. These maps serve as a basis for future research where continuous spatial estimates of root mycorrhizal stocks are needed.

Arbuscular mycorrhizal root colonization depends on the spatial distribution of the host plants

Despite their ubiquity in terrestrial ecosystems, arbuscular mycorrhizal fungi (AMF) experience dispersion constraints and thus depend on the spatial distribution of the plant hosts. Our understanding of fungal-plant interactions with respect to their spatial distributions and implications for the functioning of the symbiosis remain limited. We here manipulated the location of habitat patches of Medicago lupulina in two experiments to explore the responses of AMF root colonization and extraradical hyphae. We tested the specific hypothesis that AMF-plant habitats high in connectance would stimulate root colonization and induce denser functional root colonization (colonization rate of arbuscules plus coils) because of higher propagule availability between nearby host plant patches (experiment 1). In experiment 2, we anticipated similar responses in mixed habitats of different soil fertility, namely phosphorus-fertilized or unfertilized soil, and anticipated a higher density of extraradical hyphae in the soil connecting the habitats with increased functional root colonization. In agreement with our hypothesis, we found the highest total and functional root colonization in unfragmented micro-landscapes, describing landscapes that occur within a spatial scale of a few centimeters with the AMF-plant habitats positioned adjacent to each other. In the second experiment, overdispersed micro-landscapes promoted functional root colonization. This study provides experimental evidence that the spatial distribution of habitats can determine AMF abundance at the microscale.

Senegalia senegal (L.) Britton Response to Microbial and Manure Amendments for the Rehabilitation of Waste Rock Dumps in the Essakane Gold Mining Site, Burkina Faso

Senegalia senegal (L.) Britton (Fabaceae) is a widespread, multipurpose tree capable of colonizing disturbed Sub-Saharan mining sites given its adaptations to arid lands. The purpose of this study was to determine the potential of the association of microbial and/or manure amendments with S. senegal seedlings for the effective rehabilitation of the environment post mining. A multi-year factorial experiment involving this species was conducted in a nursery and on waste rock dumps (Essakane gold mine, NE Burkina Faso). Inoculation with arbuscular mycorrhizal (AM) fungi (native isolate Rhizophagus aggregatus DAOM2277128; commercial isolate Rhizophagus irregularis DAOM197198) and Mesorhizobium plurifarium strain ORS3588 was conducted on S. senegal seedlings. These were planted in black polythene bags filled with three substrate types: 100% sandy soil (substrate A); 75% sandy soil, 25% manure (substrate B); and 50% sandy soil, 50% manure (substrate C). Seedlings were then out-planted on waste rock to determine whether microbial inoculation improves their growth and survival rates. Under nursery conditions, manure-enriched substrates harboured less nodulation and AM colonization, but substantially increased plant height, and dry mass compared to un-amended substrate. Inoculation on manure-enrich substrates did not consistently increase root AM colonization and plant growth parameters among treatments. Plants that were inoculated with R. aggregatus alone or with R. irregularis or Mesorhizobium plurifarium ORS3588 showed the greatest increase in growth variables. On un-amended substrates, inoculation with R. aggregatus in combination with M. plurifarium or R. irregularis significantly enhanced root colonization rates, without altering plant growth parameters. Yet, inoculation with R. irregularis or M. plurifarium alone did not elicit increases in these parameters, although nodulation was greatly improved by the latter treatment. In field conditions, plant growth and survival were reduced under high rate manure amendments, likely due to less AM colonization and root nodulation that was observed for these treatments in nursery before out-planting. Strongly colonized plants on the un-amended substrate and moderately amended substrate showed greater survival after out-planting. Our results support the general conclusion that microbial inoculation and manure-enriched substrates are a viable option for mining site rehabilitation using S. senegal. They also suggest that manure amendments in forest nurseries should be cautiously applied given that high rates may impede establishment of plant symbioses, thereby affecting their performance on waste rock dumps following out-planting.

Mixture of N2-fixing tree species promotes organic phosphorus accumulation and transformation in topsoil aggregates in a degraded karst region of subtropical China

Many studies have shown that introducing N2-fixing tree species into plantations can increase soil nitrogen (N) availability, via biological N2 fixation and faster N cycling. However, the effects and regulatory mechanisms of N2-fixing tree species in planting single species vs a combination of two species on phosphorus (P) accumulation and transformation in degraded karst soils remain poorly understood and appear site-dependent. This study aimed to determine the effects of introducing N2-fixing tree species (via single species vs a combination of two species) into a degraded karst region on organic phosphorus (Po) accumulation and transformation in topsoil aggregates. A comparative experiment was performed involving 8-year-old pure plantations of Dalbergia odorifera (PD) and Acrocarpus fraxinifolius (PA), a mixed plantation of Dalbergia odorifera and Acrocarpus fraxinifolius (MP), and an adjacent natural weed field (no trees, CK) in Mashan, Guangxi, subtropical China. The results showed that the contents of soil organic carbon (SOC), nitrate nitrogen (NO3−-N), available phosphorus (AP) and C:N ratios in bulk soil and aggregates, increased significantly (P < 0.05) in MP compared to CK. The levels of soil microbial biomass N (MBN) and microbial biomass P (MBP) in bulk and aggregate soils increased significantly (P < 0.05), except for micro-aggregates (<0.25 mm) in MP samples. In contrast, no significant differences of MBN or MBP were found among PD, PA and CK plots in bulk and most aggregate soils. The phospholipid fatty acid (PLFA) contents of all microbes, bacteria, fungi, arbuscular mycorrhizal (AM) fungi and actinomycetes were also significantly higher (P < 0.05) in MP than those in CK and PD in bulk and most aggregate soils. Labile Po and highly resistant Po, and the activities of all tested N and P hydrolytic enzymes, improved in bulk soil and most aggregate size classes in all forest types, especially in MP samples. Finally, redundancy analysis (RDA) indicated that Po fractions were primarily driven by alkaline phosphatase (ALP), MBN and AM. Our findings suggest that introducing N2-fixing tree species (especially MP) may be an effective method for increasing N availability and AM colonization of roots, and thereby promoting Po accumulation and transformation in degraded karst regions of southwest China.

Environmental Conditions and Grazing Exerted Effects on Arbuscular Mycorrhizal in Plants at Southern Patagonia Rangelands

Arbuscular mycorrhizal (AM) fungi play a major role in maintaining ecosystem functions. AM fungi are found in most ecosystems including rangelands currently under increasing pressures from human activities. Southern Patagonia (Argentina) is a semiarid region influenced by extensive livestock production in rangelands. There is a lack of information about the environmental conditions and functionality of AM fungi in plant species of Patagonia ecosystems associated with livestock grazing. We assessed how soil properties, climatic conditions, and grazing intensities influence the response of AM fungi colonization. We studied most palatable and representative plant species (Poa dusenii, Rytidosperma virescens, Festuca gracillima, Nardophylum bryoides, Mulguraea tridens, and Carex argentina) growing in main ecological areas of Southern Patagonia. Most of the studied plant species (except C. argentina) presented AM symbiosis. AM colonization showed a negative relationship with soil organic carbon and nitrogen and a positive relationship with soil bulk density and pH. Results suggest that plants promoted a higher root AM colonization when soil nutrients and water availability (rainfall) are limiting. Sheep stocking rates had a differential impact depending on the ecological areas and plant life forms. High grazing decreased the AM colonization in the ecological areas with palatable plant dominance, suggesting that the impacts of grazing could lead to further negative effects on the ecosystem. Moderate grazing allows to maintain higher AM colonization, which would probably benefit the aboveground production of palatable plant and, consequently, to herbivores, particularly in degraded rangelands like Patagonian steppes. This study improves the knowledge of AM association in Patagonian semiarid rangelands by increasing our understanding of the impacts of grazing on belowground ecology. This information becomes relevant for grazing sustainable management, which may contribute to food security.

Effects of biochar amendment on wheat production, mycorrhizal status, soil microbial community, and properties of an Andisol in Southern Chile

Biochar (BC) production from agroforestry wastes and mycorrhizal fungi are potentially important agricultural practices for improving crops yields and increasing phosphorus (P) in volcanic soils. This study aimed to test the effect of BC application on wheat biomass and grain yield production, indigenous arbuscular mycorrhizal (AM) fungi propagules and soil microbial community and related to soil quality properties of an Andisol in Southern Chile. Biochars (BCs) were produced from oat hulls (OBC) and pine bark (PBC). Doses of 0, 5, 10, and 20 Mg ha−1 of BCs were applied on soil using wheat as the test crop. Wheat biomass (root and shoot portion) and grain yield, AM root colonization, spore, mycelium density, and glomalin content (glomalin related soil protein, EE-GRSP) were measured and related with soil quality properties such as bulk density, water-stable aggregates (WSA), and water holding capacity (WHC). The OBC had a significantly higher macronutrients content (N, P, K) than PBC. The highest dose of both BCs significantly improved shoot and root biomass and wheat grain yield. Application of 20 Mg ha−1 of OBC and PBC increased AM spore density and root colonization relative to control treatment. In the same way, the BC application significantly affects the AM mycelium density. The results showed that the application of higher BC dose changed the soil microbial community. The use of BCs in this volcanic soil is an effective strategy to increase wheat biomass, increase grain yield production, stimulate the indigenous AM fungi activity, enhance soil quality properties, and increase the sustainability levels of agricultural systems.

Enhancement of sorghum grain yield and nutrition: A role for arbuscular mycorrhizal fungi regardless of soil phosphorus availability

Societal Impact StatementSorghum is an important cereal crop that provides calories and nutrients for much of the world's population, and it is often grown with low fertiliser input. Optimising the yield, nutritive content and bioavailability of sorghum grain with minimal input is of importance for human nutrition, and arbuscular mycorrhizal (AM) fungi have previously shown potential to assist in this. Across sorghum genetic diversity, AM fungi improved the yield, nutrition and zinc and iron bioavailability of grain in a low phosphorus soil. Thus, food production systems that effectively manage AM fungi may improve consumer outcomes.Summary Sorghum is a C4 cereal crop that is an important source of calories and nutrition across the world, predominantly cultivated and consumed in low‐ and middle‐income countries. Sorghum can be highly colonised by arbuscular mycorrhizal (AM) fungi, and the plant‐fungal association can lead to improvements in biomass and nutrient uptake. High‐throughput phenotyping allows us to non‐destructively interrogate the ‘hidden’ effects of AM fungi on sorghum growth and phenology. Eight genetically diverse sorghum genotypes were grown in a soil amended with 2 or 20 mg P kg−1 and inoculated with an AM fungal culture of Rhizophagus irregularis. High‐throughput phenotyping uncovered the ‘hidden’ effects of AM fungi on growth and phenology, while grain biomass, nutrition, Zn and Fe bioavailability and root AM colonisation was determined after destructive harvest. Sorghum plants colonised by AM fungi generally performed better than non‐AM control plants, with greater yield, harvest indices, and grain P, Zn and Fe contents. During the early growth stages, AM colonisation led to temporary growth depressions. There were also AM fungal and P fertilisation effects on sorghum time‐of‐flowering. The sorghum genotype with the highest AM colonisation could barely produce grain when non‐inoculated. The two genotypes that failed to mature had very low AM colonisation. Generally, the genetically diverse sorghum genotypes were highly responsive to AM colonisation and produced more grain of greater nutritive quality when colonised, without adverse consequences for micronutrient bioavailability.

The enhanced phosphorus use efficiency in phosphate-deficient and mycorrhiza-inoculated barley seedlings involves activation of different sets of PHT1 transporters in roots.

Transcriptional activation of subfamily II PHT1 members in roots is associated with the enhanced phosphorus use efficiency and growth promotion of barley seedlings inoculated with Glomus species. The arbuscular mycorrhizal (AM) fungi symbiotic associations in cereal crops are known to regulate growth in cultivar-specific manner and induce phosphate (Pi) transporters (PHT1) in roots. In the present study, we observed that both AM colonization of roots by Glomus species and phosphate starvation enhanced phosphorus use efficiency (PUE) in barley seedlings. Our search for the full complement of PHT1 members in the recently sequenced barley genome identified six additional genes, totaling their number to 17. Both AM colonization and Pi starvation triggered activation of common as well as different PHT1s. Pi starvation led to the robust upregulation of HvPHT1;6.2/6.3 at 7d and weak activation of HvPHT1;1 in shoots at 3d time-point. In roots, only HvPHT1;1, HvPHT1;6.2/6.3, HvPHT1;7, HvPHT1;8, HvPHT1;11.2 and HvPHT12 were induced at least one of the time-points. AM colonization specifically upregulated HvPHT1;11, HvPHT1;11.2, HvPHT1;12 and HvPHT1;13.1/13.2, members belonging to subfamily II, in roots. Sucrose availability seems to be obligatory for the robust activation of HvPHT1;1 as unavailability of this metabolite generally weakened its upregulation under Pi starvation. Intriguingly, lack of sucrose supply also led to induction of HvPHT1;5, HvPHT1;8, and HvPHT1;11.2 in either roots or shoot or both. The mRNA levels of HvPHT1;5 and HvPHT1;11.2 were not severely affected under combined deficiency of Pi and sucrose. Taken together, this study not only identify additional PHT1 members in barley, but also ascertain their AM, Pi and sucrose-specific transcript accumulation. The beneficial role of AM fungi in the promotion of PUE and barley seedlings' growth is also demonstrated.

Short-term microbial responses to soluble inorganic P input in a tropical lowland rain forest in Amazonia

In non-flooded lowland rain forests with low soil phosphorus (P) in parts of Amazonia, P cycling largely occurs via leaf litter recycling by arbuscular mycorrhizal (AM) fungal symbionts. Occasional high input of P into these ecosystems occurs during drought years with increased litterfall. As the length and frequency of drought events are projected to increase in the region, a single-dose nutrient addition experiment was carried out to test how this would impact P cycling. An application rate of 4 kg P ha–1 was used, which corresponds to twice the amount of litter-derived P in an average year. It was hypothesized that i) the added mineral P would be immobilized by soil microorganisms, leading to measurable increase in soil microbial biomass carbon (C) and P and ii) AM colonization rate would be reduced by the pulse in mineral P available for plant uptake. The results did not support either of our hypotheses. The addition of P did not have an effect on AM root colonization, nor was P immobilized by soil microbiota during the experimental period. The lack of a difference between the control and treatment at our study site could be attributed to the relatively low one-off dose of P applied that did not change either the colonization rate of roots by AM fungi or the amount of soil available labile P. To obtain a mechanistic understanding of the availability, capture, and use of P by plant-symbiont associations in tropical rain forest ecosystems, further integrated studies of the soil-plant system combining long-term nutrient manipulations, modeling, and experimental approaches are required.

The relative contribution of indigenous and introduced arbuscular mycorrhizal fungi and rhizobia to plant nutrient acquisition in soybean/maize intercropping in unsterilized soils

It has been demonstrated that intercropped crops may benefit from inoculation with rhizobia or arbuscular mycorrhizal (AM) fungi in soybean/maize intercropping systems under sterilized conditions. Little is known about the relative contribution of indigenous and introduced AM fungi and rhizobia to nutrient acquisition of intercropped soybean and maize in unsterilized soils. In this study, we evaluated the effectiveness of indigenous and introduced AM fungi and rhizobia in a soybean/maize intercropping system under unsterilized soil conditions. The results show that introduced rhizobial inoculation promoted soybean nodulation and growth. Single AM fungal inoculation promoted indigenous rhizobial nodulation and increased maize AM root colonization, but had little effect on maize growth. Co-inoculation strongly increased plant dry weight, and nitrogen (N) and phosphorus (P) content of the intercropped soybean compared to those with only indigenous rhizobial and AM fungal communities, but had no effect on those of maize in the same intercropped system. These results indicate that AM fungal inoculation promoted nodulation by indigenous rhizobia. Effective rhizobial inoculation combined with introduced AM fungi may not only promote symbiotic N2 fixation, but also enhance rhizosphere processes, which has the potential to improve nutrient acquisition in the field. Soybean is a weak competitor compared with maize in intercropping systems. Inoculation with introduced AM and rhizobia ameliorated the growth suppression of intercropped soybean, but inhibited growth of intercropped maize, indicating that inoculation of introduced AM fungi and/or rhizobia partly shifted the competitive advantage from maize to soybean. In conclusion, introduced AM fungi and rhizobia contributed more than indigenous populations to promoting growth and nutrient acquisition of the intercropped soybean in unsterilized soils.

Irrigation and fertilization effects on arbuscular mycorrhizal fungi depend on growing season in a dryland maize agroecosystem

Arbuscular mycorrhizal (AM) fungi form mutualistic associations with most terrestrial plants and can enhance crop water and nutrition acquisition. It is thus important to elucidate the interactive impacts of water and fertilizer management on AM fungi for sustainable agriculture. Our study investigated the effects of irrigation (well-watered vs. drought) and fertilization (nitrogen (N), phosphorus (P), and NP) on AM fungi in soil and roots of maize (Zea mays L.) across three consecutive growth phases (jointing, tasseling, and mature). Drought significantly decreased AM fungal extra-radical hyphal density and root colonization rate at the tasseling and mature phases, respectively. Nitrogen and NP fertilization exerted a negative effect on AM fungal spore density under drought at the mature phase. Drought decreased AM fungal richness in soil and roots at the jointing and mature phases, respectively. AM fungal community composition in soil and roots was significantly different between the jointing phase and the tasseling and mature phases. AM fungal community composition was influenced by fertilization at the tasseling phase in soil, but by irrigation at the jointing and tasseling phases in roots. Our findings highlight the differential response of AM fungi in soil and roots to drought and fertilization during the various phases of maize development in this dryland agroecosystem.

Diversity of arbuscular mycorrhizal (AM) fungi in mangroves of Chorao Island, Goa, India

For a desirable understanding of diversity and species composition of arbuscular mycorrhizal (AM) fungi, in true and associate mangrove plants, 17 true mangrove and their associate species belonging to ten families were assessed from Chorao Island, Goa, India. Maximum AM root colonization was recorded in Thespesia populnea and minimum in Avicennia marina. Rhizosphere soils of Ceriops tagal showed highest and that of Acrostichum aureum showed the least spore density. The results showed that the associate mangrove species were highly mycorrhizal compared to true mangrove plants. Our study recorded greater diversity involving thirty-two AM fungal species belonging to nine genera viz., Acaulospora, Claroideoglomus, Entrophospora, Funneliformis, Gigaspora, Glomus, Rhizophagus, Sclerocystis, and Scutellospora. Acaulospora was the dominant genus and A. dilatata was the dominant AM fungal species. Acaulospora dilatata was the most common AM species in both true and associate mangrove plants, revealing its wider adaptability.

Suitability of Mycorrhiza-Defective Rice and Its Progenitor for Studies on the Control of Nitrogen Loss in Paddy Fields via Arbuscular Mycorrhiza.

Employing mycorrhiza-defective mutants and their progenitors does not require inoculation or elimination of the resident microbial community in the experimental study of mycorrhizal soil ecology. We aimed to examine the suitability of mycorrhiza-defective rice (non-mycorrhizal, Oryza sativa L., cv. Nipponbare) and its progenitor (mycorrhizal) to evaluate nitrogen (N) loss control from paddy fields via arbuscular mycorrhizal (AM) fungi. We grew the two rice lines in soils with the full community of AM fungi and investigated root AM colonization. In the absence of AM fungi, we estimated rice N content, soil N concentration and microbial community on the basis of phospholipid fatty acids; we also quantified N loss via NH3 volatilization, N2O emission, runoff and leaching. In the presence of AM fungi, we did not find any evidence of AM colonization for non-mycorrhizal rice while mycorrhizal rice was colonized and percentage of root colonization was 17–24%. In the absence of AM fungi, the two rice lines had similar N content, soil N concentration and microbial community. Importantly, there was no significant difference in N loss via all the four pathways between mycorrhizal and non-mycorrhizal systems. This mycorrhizal/non-mycorrhizal rice pair is suitable for further research on the role of AM fungi in the control of soil N loss in paddy fields.

Composition of the arbuscular mycorrhizal fungal community and changes in diversity of the rhizosphere of Clematis fruticosa over three seasons across different elevations

AbstractClematis fruticosa Turcz. is a dominant native shrub with the potential for spontaneous vegetation succession for restoration of the ecologically fragile and arid Daqing Mountains of Inner Mongolia, which represent an important ecological transition zone in northern China. However, knowledge regarding the interactions between native species and their root‐associated arbuscular mycorrhizal (AM) fungi across different seasons and elevation gradients remains obscure. High AM fungal spore density, root colonization and arbuscular richness suggested that C. fruticosa could establish intimate symbiotic associations with AM fungi. A total of 174 AM fungal virtual taxa were identified from rhizosphere soil samples, and Glomus was dominant. The most distinct AM fungal community composition and the greatest richness and diversity were observed in the spring and at the highest elevation. Seasons • elevation interactions significantly affected Simpson diversity but not AM fungal community composition, observed richness and Shannon index. Seasons had a significant direct on AM fungal observed richness and Shannon index, and elevation had a significant direct on AM fungal observed richness. Soil available phosphorus was the most important driving factor in AM fungal richness and diversity, followed by seasons and soil moisture content. These results provied new insights suggesting that there are active and diverse “functional ingredients”, for example root‐associated AM fungi during the growing season, particularly with an earlier onset in the spring. They are potentially major contributors to the re‐vegetation of degraded lands and the maintenance of soil structure in arid and semiarid ecosystems, which is attributable to seasonal variation in host physiology in stressful environments.Highlights We studied the effects of seasons and elevation on AM fungal richness, diversity and community in ecologically fragile mountain areas. Distinct community composition and greater richness and diversity of AM fungi were detected in the spring and at the highest elevation. AM fungal richness and diversity depended on certain soil variation related to seasons and elevation.

Arbuscular mycorrhizal fungal community was affected by tillage practices rather than residue management in black soil of northeast China

Arbuscular mycorrhizal (AM) fungi are one of the most important soil microbes in an agrarian ecosystem, and consequently affected by various agricultural practices. To elucidate the effects of tillage practices and residue management on AM fungi, a field trial was conducted on the Songnen Plain, Northeast China. We examined the effects of different tillage practices including no-tillage (NT), rotary tillage (RT), subsoil tillage (ST) and deep tillage (DT) on the AM fungal biomass, diversity and community under residue removal and residue retention. AM root colonization and extraradical hyphal (ERH) density were significantly higher in DT treatment compared with NT treatment, whereas an opposite trend was observed for AM fungal spore density. Structural equation modeling indicated that AM fungal spore density was directly affected by tillage practices. Albeit, the effect of tillage practices on ERH density was mainly mediated through root length of maize. By Miseq sequencing of 18S rDNA, 66 AM fungal operational taxonomic units (OTUs) were identified and Glomeraceae was the most abundant group in this study. AM fungal OTU richness was highest in treatment NT, and significantly higher than that in treatment DT. Non-metric multidimensional scaling analysis indicated that treatment DT and ST induced a distinct AM fungal community composition compared with treatment NT. On the other hand, residue did not significantly influence AM fungal biomass, OTU richness and community composition. Overall, our findings indicated that tillage practice is a stronger determinant than residue management in AM fungal development and community composition in black soil on the Songnen Plain.

Efficiency of two arbuscular mycorrhizal fungal inocula to improve saline stress tolerance in lettuce plants by changes of antioxidant defense mechanisms.

Arbuscular mycorrhizal (AM) fungi establish symbioses with most agricultural plants and improves growth under soil stress conditions. The present study aimed to evaluate the functional contribution of 2 AM fungal inocula (a native consortium isolated from saline soils of the Atacama Desert, 'HMC', and a reference inoculum Claroideoglomus claroideum, 'Cc') on the growth and antioxidant compounds of two cultivars of lettuce (Lactuca sativa cvs. 'Grand Rapids' and 'Lollo Bionda') at increasing salt stress conditions (0, 40, and 80 mmol L-1 NaCl). At 60 days of plant growth, the symbiotic development, biomass production, lipid peroxidation, proline content, antioxidant enzymes, phenolic compound profiles and antioxidant activity were evaluated. The 2 AM inocula differentially colonized the roots of Grand Rapids and Lollo Bionda lettuce plants. The AM symbioses increased proline synthesis and superoxide dismutase, catalase and ascorbate peroxidase activities and diminished phenolic compound synthesis and oxidative damage in lettuce, which was related positively to a higher growth of inoculated plants under salt exposure. The higher concentration of phenolic compounds induced by salinity in non-inoculated plants was associated with high oxidative stress and low fresh biomass production. Modulation of salinity stress in lettuce by AM root colonization is a result of changes of antioxidant enzymatic systems that reduce oxidative damage and sustain growth. The application of AM fungi to improve crop production by means of directed inoculation with efficient AM fungal strains may enhance lettuce production on soils plagued with salinity worldwide. © 2019 Society of Chemical Industry.