Hyphae Of Arbuscular Mycorrhizal Fungi Research Articles

Spatial Distribution of Glomalin-related Soil Proteins in Coniferous and Broadleaf mixed Temperate Forest

Glomalin-related soil protein (GRSP), as an important component of soil organic carbon (SOC) pool, is a glycoprotein produced by the hyphae of arbuscular mycorrhizal fungi (AMF), which play a vital role in carbon and nutrient cycling in forest ecosystem. Here we investigated the spatial distribution of GRSP in plant community of the dominated species not associated with AMF based on a typical coniferous and broad-leaved temperate forest in Mt. Changbai, Northeastern China. Spatial distribution of GRSP including easily extractable GRSP (EEG) and total GRSP (TG) is represented by Moran’s I on different soil depth among seven soil layers of 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-50 cm, 50-70 cm and 70-100 cm. The concentrations of EEG and TG decreased with the increase of soil depth according to a logarithmic function. The Moran’s I coefficient of GRSP was negative in all soil layers except TG in 20-30 cm and 50-70 cm soil layers. When EEG and TG were considered, the Moran’s I coefficient was positive in majority of soil layers within the separation distance of less than 4 m but in soil layers of 10-20 cm and 20-30 cm for EEG and in 30-50 cm for TG. The largest Moran’s I coefficient including EEG and TG was observed in the soil layer of 5-10 cm. The spatial distribution of GRSP was discrete in typical coniferous and broad-leaved temperate forest, and was affected by mycorrhizal colonization rate, soil organic carbon and total nitrogen.
 
 *********
 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
 *********

Secretion of acid phosphatase from extraradical hyphae of the arbuscular mycorrhizal fungus Rhizophagus clarus is regulated in response to phosphate availability.

Arbuscular mycorrhizal (AM) fungi increase phosphate (P) uptake by plants. Organic phosphate comprises 30-80% of total P in most agricultural soils. Some plants can utilize organic phosphate by secreting acid phosphatase (ACP) from their roots, especially under low P conditions. Although secretion of ACP from extraradical hyphae of AM fungi has been reported, the specific factors that affect the secretion of ACP are unknown. The objective of the present study was to investigate whether secretion of ACP from extraradical hyphae is induced by low P conditions. First, specimens of Allium fistulosum were either inoculated with the AM fungus Rhizophagus clarus strain CK001 or remained uninoculated and were grown in soil with 0.5 g P2O5 kg-1 soil or without P fertilization using two-compartment pots. Soil solution was collected using mullite ceramic tubes 45 days after sowing. The soil solution was analyzed for ACP activity by using p-nitrophenylphosphate. Second, Ri T-DNA transformed roots (i.e., hairy roots) of Linum usitatissimum inoculated with R. clarus were grown on solid minimal media with two P levels applied (3 and 30 μM P) using two-compartment Petri dishes under in vitro conditions. Hyphal exudates, extraradical hyphae, and hairy roots were collected and analyzed for ACP activity. ACP activity in the soil solution of the hyphal compartment in the A. fistulosum inoculation treatment was higher without P fertilization than with P fertilization. AM colonization also was higher without P fertilization than with P fertilization. In the in vitro two-compartment culture, ACP activity of hyphal exudates and extraradical hyphae were higher under the 3-μM treatment than under the 30-μM treatment. These findings suggest that the secretion of ACP from the extraradical hyphae of R. clarus into the hyphosphere is promoted under low P conditions.

HCN‐producing Pseudomonas protegens CHA0 affects intraradical viability of Rhizophagus irregularis in Sorghum vulgare roots

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria inhabit the plant rhizosphere. Both functional groups can influence plant community structures, and interactions between them can vary from being synergistic to antagonistic. HCN-producing Pseudomonas protegens CHA0 is a plant growth-promoting rhizobacterium. P. protegens CHA0 has been shown to weakly attach to AMF hyphae. Here, we analyze the effect of P. protegens CHA0 on the viability of intraradical AMF hyphae. Using pot experiments, we have grown mycorrhizal and nonmycorrhizal Sorghum vulgare var. M35 with P. protegens CHA0 or HCN- mutant P. protegens CHA77, which did not produce HCN. Mycorrhizal and nonmycorrhizal Sorghum grown without CHA0 or CHA77 served as the control. While metabolically active AMF was not detected in mycorrhizal plants grown with HCN+ CHA0, the percentage of root colonization of metabolically active AMF in plants grown with HCN- CHA77 was lower than in the control. Root phosphorus was highest in mycorrhizal plants grown with HCN+ CHA0, but root Fe was higher in plants grown with the bacterial strains. Our results indicate that HCN-producing P. protegens can affect the viability of intraradical AMF.

Tall Fescue and E. coenophiala Genetics Influence Root-Associated Soil Fungi in a Temperate Grassland.

A constitutive, host-specific symbiosis exists between the aboveground fungal endophyte Epichloë coenophiala (Morgan-Jones & W. Gams) and the cool-season grass tall fescue (Lolium arundinaceum (Schreb.) Darbysh.), which is a common forage grass in the United States, Australia, New Zealand, and temperate European grasslands. New cultivars of tall fescue are continually developed to improve pasture productivity and animal health by manipulating both grass and E. coenophiala genetics, yet how these selected grass-endophyte combinations impact other microbial symbionts such as mycorrhizal and dark septate fungi remains unclear. Without better characterizing how genetically distinct grass-endophyte combinations interact with belowground microorganisms, we cannot determine how adoption of new E. coenophiala-symbiotic cultivars in pasture systems will influence long-term soil characteristics and ecosystem function. Here, we examined how E. coenophiala presence and host × endophyte genetic combinations control root colonization by belowground symbiotic fungi and associated plant nutrient concentrations and soil properties in a 2-year manipulative field experiment. We used four vegetative clone pairs of tall fescue that consisted of one endophyte-free (E−) and one E. coenophiala-symbiotic (E+) clone each, where E+ clones within each pair contained one of four endophyte genotypes: CTE14, CTE45, NTE16, or NTE19. After 2 years of growth in field plots, we measured root colonization of arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE), extraradical AMF hyphae in soil, total C, N, and P in root and shoot samples, as well as C and N in associated soils. Although we observed no effects of E. coenophiala presence or symbiotic genotype on total AMF or DSE colonization rates in roots, different grass-endophyte combinations altered AMF arbuscule presence and extraradical hyphal length in soil. The CTE45 genotype hosted the fewest AMF arbuscules regardless of endophyte presence, and E+ clones within NTE19 supported significantly greater soil extraradical hyphae compared to E− clones. Because AMF are often associated with improved soil physical characteristics and C sequestration, our results suggest that development and use of unique grass-endophyte combinations may cause divergent effects on long-term ecosystem properties.

Impacts of core rotation, defaunation and nitrogen addition on arbuscular mycorrhizal fungi, microorganisms and microarthropods in a tropical montane rainforest

In tropical ecosystems, interactions between arbuscular mycorrhizal fungi (AMF) and other organisms have been little studied, but may be of significant importance for understanding the role of AMF in decomposition processes and nutrient cycling. In this study, we used ingrowth cores to investigate the impacts of regular rotation of the cores, defaunation and nitrogen addition on AMF, microbial biomass and microarthropods in the fermentation/humus (F/H) and litter (L) layers of an Ecuadorian montane tropical rainforest. AMF were substantially reduced in the F/H layer (to 34% of initial), while in the L layer they remained constant during the experiment. Overall, microorganisms and microarthropods were largely independent of AMF hyphae and their exudates, however, defaunation strongly affected the recovery of their communities. Nitrogen addition increased the quality of litter material and beneficially affected microbial communities thereby increasing decomposition rates, but did not impact AMF abundance and microarthropod communities. These findings suggest that the cutoff of the carbon supply from the plant to the fungal mycelium was not compensated by switching resources in the F/H layer, underlining a strong association between AMF and living roots. While in the L layer, AMF likely competed with saprotrophic microorganisms for litter-derived resources at intermediate stages of decomposition pointing to indirect contributions of AMF to decomposition processes. Overall, the results support the view that root-derived resources are important in fueling soil food webs, but also indicate that in the studied montane rainforest these resources are only available close to roots and not channeled distant to roots via AMF.

Biogeography of arbuscular mycorrhizal fungal communities in saline ecosystems of northern China

Arbuscular mycorrhizal (AM) fungi, influencing many important ecosystem processes, widely occur in saline soils, and thus understanding their biogeographic patterns is of primary interest in saline ecosystem restoration. Fine roots and rhizosphere soils were sampled in black locust (Robinia pseudoacacia) plantations in four saline sites in northern China to detect soil properties and AM fungal attributes including their colonization level, spore density, hyphal density and community composition. Arbuscular mycorrhizal fungal attributes varied with sampling sites, and this variation was mostly attributed to changes in habitat characteristics and geographic distance. Habitat characteristics shape the root- and soil-inhabiting AM fungal communities to the same extent, whereas geographic distance seems to contribute more to root-inhabiting AM fungal assemblages. The level of root colonization by vesicles, arbuscules and hyphae and the density of AM fungal spores and hyphae in soils were found to be related to the relative abundance of AM fungal species such as root-inhabiting Rhizophagus intraradices and soil-inhabiting Sclerocystis sinuosa. All the results suggest that changes in habitat characteristics and geographic distance may induce biogeographic patterns of AM fungi, and these patterns are closely related to AM symbiosis in roots and the development of AM fungi in soils.

Mycorrhizal colonization of indigenous tropical tree species grown in peat swamp forests of Sumatera, Indonesia

The restoration of peat swamp forests in Sumatra island has become Indonesian government’s priority to restore ecological functions and their utilization. Indigenous. However, little information is available on the status of arbuscular mycorrhizal (AM) fungi in Sumatera. The objective of this research was to know AM fungi colonization in indigenous of tropical peat swamp forests. Root samples of 28 tree species in 14 families grown in a peat swamp forest of Jambi, Riau, and South Sumatera. All soil and tree roots were grown in zeolite media and trapped in Pueraria javanica and Shorgum bicolor as host plants for four months in a green house. Roots were stained with 0.1% trypan blue and vesicles, arbuscles and internal hyphae of AM fungi observed under a compound microscope. The results have shown that 20 tree species (72%) were colonized by AM fungi, 4 tree species of the dipterocarps family (14%) were colonized by ectomycorrhizal fungi (ECM), and four other tree species (14%) did not find FMA or ECM colonization. It is suggested that utilization of mycorrhizas can increase early growth of some tree species grown in peat swamp forests and mycorrhizal application will be expected as a key technology to restore degraded peatlands.

Decomposition rate of extraradical hyphae of arbuscular mycorrhizal fungi decreases rapidly over time and varies by hyphal diameter and season

Understanding how extraradical mycorrhizal fungal hyphae (EMH) regulate the cycling and retention of plant-assimilated carbon (C) in forest soils requires estimation of the production, mortality, and decomposition of EMH. To do this, the use of mass-balance models in combination with hyphal in-growth mesh bags (“in-growth bags”) was proposed in recent studies. However, poor knowledge on the decomposition of field-grown EMH prevents confirmation of assumed EMH decomposition dynamics. In this study, we determined the decrease in hyphal length density of field-grown EMH of arbuscular mycorrhizal fungi (AM) over eight months in in-growth bags incubated in a warm-temperate Chamaecyparis obtusa forest, to study EMH decomposition under field conditions. We used exponential decay models to describe the changes in the decomposition rate of EMH over the incubation time, between EMH diameter classes, and between seasons. A rapid decrease of the decomposition rate of EMH within two months from 2.5 to 0.1 month−1 was estimated, corresponding to an increase in half-life from 0.3 to 7 months. Furthermore, significant differences in the initial maximum decomposition rate were estimated between fine (1.6 month−1; minimum half-life: 0.4 months) and coarse EMH (3.1 month−1; minimum half-life: 0.2 months) and between incubations during spring-summer (April and August; 2.7 month−1; minimum half-life: 0.3 months) and autumn-winter (October and February; 1.1 month−1; minimum half-life: 0.6 months). This large variability in the decomposition rates of EMH of AM fungi has to be considered in mass-balance models to estimate C fluxes between plants, soil, and the atmosphere.

Soil respiration in a tropical montane grassland ecosystem is largely heterotroph-driven and increases under simulated warming

Soil respiration, a major source of atmospheric carbon (C), can feed into climate warming, which in turn can amplify soil CO2 efflux by affecting respiration by plant roots, arbuscular mycorrhizal fungi (AMF) and other heterotrophic organisms. Although tropical ecosystems contribute >60% of the global soil CO2 efflux, there is currently a dearth of data on tropical soil respiration responses to increasing temperature. Here we report a simulated warming and soil respiration partitioning experiment in tropical montane grasslands in the Western Ghats in southern India. The study aimed to (a) evaluate soil respiration responses to warming, (b) assess the relative contributions of autotrophic and heterotrophic components to soil respiration, and (c) assess the roles of soil temperature and soil moisture in influencing soil respiration in this system. Soil respiration was tightly coupled with instantaneous soil moisture availability in both the warmed and control plots, with CO2 efflux levels peaking during the wet season. Soil warming by ˜1.4 °C nearly doubled soil respiration from 0.62 g CO2 m−2 hr−1 under ambient conditions to 1.16 g CO2 m−2 hr−1 under warmed conditions. Warming effects on soil CO2 efflux were dependent on water availability, with greater relative increases in soil respiration observed under conditions of low (with a minimum of 2.6%), compared to high (with a maximum of 64.3%), soil moisture. Heterotrophs contributed to the majority of soil CO2 efflux, with respiration remaining unchanged when roots and/or AMF hyphae were excluded as the partitioning treatments were statistically indistinguishable. Overall, our results indicate that future warming is likely to substantially increase the largely heterotroph-driven soil C fluxes in this tropical montane grassland ecosystem.

Disentangling direct and indirect effects of mycorrhiza on nitrous oxide activity and denitrification

Nitrous oxide (N2O) is a potent greenhouse gas emitted at considerable rates from agricultural soils. A few recent studies have indicated the potential to reduce N2O emission rates in agricultural systems through management of soil microbiota, such as mycorrhizal fungi. Our limited understanding of how mycorrhiza influences N2O emission rates, however, forestalls such management practices. To address the knowledge gap regarding the mechanism of mycorrhizal modification of N2O formation and denitrification, we disentangle the direct effects of arbuscular mycorrhizal fungi (AMF) via hyphal growth on potential denitrification activity from those resulting from indirect AMF-induced changes in soil aggregation. We manipulated AMF status in a factorial experiment through adding or not AMF inoculum in the form of Rhizophagus irregularis and soil aggregation state through either crushing soil aggregates or using agricultural soil with intact soil aggregates. We then grew Zea mays (maize) in compartmentalized mesocosms for 4 months. At harvest, we observed approximately three-fold higher AMF root colonization and hyphal densities in the treatments where we had added Rhizophagus irregularis. Potential N2O activity rates and the denitrification ratio were higher in the undisturbed soil and in the mesocosms with a dense AMF hyphal network (direct effect of mycorrhiza). Further, AM-hyphae promoted soil aggregation while also altering potential denitrification activity (indirect effect of mycorrhiza). Overall, we present here a comprehensive case study on how mycorrhiza alters potential denitrification activity and related N2O activity from agricultural soils.

Aphids can acquire the nitrogen delivered to plants by arbuscular mycorrhizal fungi

Abstract Above‐ and below‐ground organisms can interact by altering the quality of shared host plants. Arbuscular mycorrhizal fungi (AMF) influence plant nutrient uptake, including nitrogen (N) acquisition. Under low N and phosphorus conditions, AMF delivery of N from organic sources not immediately available to the plant can have large impacts on plant N status, a limiting nutrient in the aphid diet. This study investigated the effect of AMF colonisation upon aphid number and determined the consequences of AMF directly accessing an organic nutrient patch that the plant cannot. We hypothesised that AMF colonisation of plants will increase plant and aphid N status, plant performance and aphid number, but only when the AMF had direct access to the added organic patch. Barley plants hosting the grain aphid Sitobion avenae were colonised by the AMF, Funneliformis mosseae, or no AMF. A two‐compartment microcosm was used to separate the plant roots from a 15N‐labelled organic patch in a second compartment. AMF‐colonised plants, but without access to the second compartment, were used to examine the effect of AMF colonisation on aphid number. In a separate treatment, and to determine whether AMF access to a plant inaccessible N source modified the effect of AMF colonisation on aphid number, AMF hyphae were permitted access to the second compartment containing an organic patch. As a control for AMF accessing a larger substrate volume, AMF were allowed access to a second compartment without an organic patch. When the AMF accessed the organic patch, more N from the patch was delivered to the plant resulting in a higher grain N concentration although plant growth was depressed. More N from the patch was also delivered to the aphids, but the N status of the aphid remained unchanged. Regardless of the level of access to the organic patch, AMF colonisation did not affect aphid number. Our data show that by accessing N sources not readily available to plants, AMF can indirectly deliver N to above‐ground organisms, a finding which has major implications for N‐transfer between higher trophic levels. A plain language summary is available for this article.

Extensive membrane systems at the host-arbuscular mycorrhizal fungus interface.

During arbuscular mycorrhizal (AM) symbiosis, cells within the root cortex develop a matrix-filled apoplastic compartment in which differentiated AM fungal hyphae called arbuscules reside. Development of the compartment occurs rapidly, coincident with intracellular penetration and rapid branching of the fungal hypha, and it requires much of the plant cell's secretory machinery to generate the periarbuscular membrane that delimits the compartment. Despite recent advances, our understanding of the development of the periarbuscular membrane and the transfer of molecules across the symbiotic interface is limited. Here, using electron microscopy and tomography, we reveal that the periarbuscular matrix contains two types of membrane-bound compartments. We propose that one of these arises as a consequence of biogenesis of the periarbuscular membrane and may facilitate movement of molecules between symbiotic partners. Additionally, we show that the arbuscule contains massive arrays of membrane tubules located between the protoplast and the cell wall. We speculate that these tubules may provide the absorptive capacity needed for nutrient assimilation and possibly water absorption to enable rapid hyphal expansion.

Integrated reclamation of saline soil nitrogen transformation in the hyphosphere by earthworms and arbuscular mycorrhizal fungus

Soil salinization greatly alters nitrogen cycling and threatens the sustainable productivity of food production areas worldwide. A two-compartment microcosm was used to investigate the integrated effects of arbuscular mycorrhizal fungi (AMF) hyphae and earthworms on nitrogen transformation at different incubation times in saline soil. The treatments were designed with or without hyphae and with or without earthworms harvested at day 40 or 60 in the hyphal compartments (HC). Salt concentration, soil aggregate-size distribution, soil organic carbon, hyphal length density (HLD), total glomalin-related soil protein (TGRSP), inorganic nitrogen concentrations, microbial biomass nitrogen (MBN) and the N-functional marker genes were determined in the HC. The results showed that earthworms and AMF hyphae decreased the soil salt concentration, while increased the soil NO3−-N, NH4+-N, MBN and the abundance of nifH and AOB amoA genes. Earthworms and AMF hyphae could independently or cooperatively affect soil macroaggregates. Earthworms and AMF hyphae affected soil NH4+-N and NO3−N by increasing the soil macroaggregates and MBN. At day 60, earthworms affected soil NO3−N by regulating the abundance of nifH and AOB amoA genes, while AMF hyphae increased soil NH4+-N by regulating the HLD and TGRSP. In conclusion, earthworms and AMF hyphae cooperatively affected soil NO3−-N and NH4+-N by regulating the soil macroaggregates, microbial biomass nitrogen and N-cycling bacteriain saline soil. The results would be useful in reclamation programmes undertaken to rehabilitate land sources that suffer from problems associated with soil salinization.

Intercropping with sweet corn (Zea mays L. var. rugosa Bonaf.) expands P acquisition channels of chili pepper (Capsicum annuum L.) via arbuscular mycorrhizal hyphal networks

Intercropping of chili pepper (Capsicum annuum L.) with corn (Zea mays L.) is one of the main valuable intercropping patterns. However, the potential contribution of arbuscular mycorrhizal (AM) fungal hyphal networks is still poorly understood. The purpose of this work was to resolve the changes of AM fungal propagation and colonization in the pepper/corn intercropping systems due to the constitution of hyphal networks and the networks’ effects on plant nutrient uptake and interspecific competitive relations. An 18-week pot experiment on an unsterilized soil was carried out to test mycorrhizal performance and P acquisition of chili pepper and sweet corn (Zea mays L. var. rugosa Bonaf.) in two compartments, which were absolutely separated (Sep) by polyvinyl chloride (PVC) layer or semi-separated (Semi-Sep) by nylon mesh (30 μm) screen that only allows the passage of AM fungal hyphae but not plant roots. Root mycorrhizal colonization rates and the biomasses and P concentrations of shoots, roots, and fruits of pepper and corn were all measured. The total P acquisition of each crop per pot and the acquisition ratio of one to two crops were assessed. Soil pH, organic C, total P, available P, AM fungal abundance, and acid phosphatase activity were also tested. In the Sep system, root mycorrhizal colonization, P acquisition amount, shoot biomass, and rhizosphere AM fungal abundance of corn were all higher (P < 0.05) than those of pepper, but soil available P concentration was lower (P < 0.05) in corn compartment than in pepper one. Compared with Sep, Semi-Sep had higher (P < 0.05) mycorrhizal colonization rates with both intercrops and higher (P < 0.05) soil acid phosphatase activity and AM fungal abundance in corn and pepper compartments, respectively. Semi-Sep decreased (P < 0.05) soil available P concentrations with both compartments, but did not narrow the difference of soil available P concentration between compartments, suggesting there was no gradient diffusion of soil available P between compartments. Semi-Sep increased (P < 0.05) the P acquisition ratio and fruit yield of pepper, but not corn. Constitution of hyphal networks increased mycorrhizal colonization with both intercrops, and corn supplied part of photosynthetic C for increasing AM fungal propagules in pepper compartment by gradient expansion since AM fungi formed better symbioses with corn. Hyphal networks increased pepper fruit yield via improving P distribution to pepper, but acquired relatively higher P from corn compartment via elevating the soil acid phosphatase activity, suggesting enhanced P competitive ability of pepper against corn upon hyphal networks.

Arbuscular mycorrhizal mycelial networks and glomalin-related soil protein increase soil aggregation in Calcaric Regosol under well-watered and drought stress conditions

Arbuscular mycorrhizal (AM) fungi have a direct influence on soil aggregation in most fertile ecosystems. This study investigated the effects of AM fungi on soil aggregate stability of Calcaric Regosol under well-watered and drought stress conditions. A two-compartment system was employed to exclude the effects of plant roots, and ultrasonic dispersion technique was applied to evaluate the aggregate bond energy. The results showed that good symbiotic relationships were formed between AM fungi and sandstorm-tolerant species Astragalus adsurgens Pall even under drought stress conditions. Inoculation with AM fungi significantly improved plant growth, especially the root development. Hyphal length, spore density, glomalin-related soil protein content were significantly increased by AM fungal inoculation under both well-watered and drought stress conditions. Likewise, the proportion and dispersive energy of soil water-stable macroaggregates were also markedly increased by the inoculation. The hyphae of AM fungi directly contributed to the dispersive energy of soil water-stable macroaggregates and significantly improved soil aggregate stability under both experimental conditions. This study demonstrates that AM fungi play a dominant role in the stability of soil water-stable aggregates by improving the aggregate bond energy, particularly for macroaggregates.

Rapid temporal changes in root colonization by arbuscular mycorrhizal fungi and fine root endophytes, not dark septate endophytes, track plant activity and environment in an alpine ecosystem.

Fungal root endophytes play an important role in plant nutrition, helping plants acquire nutrients in exchange for photosynthates. We sought to characterize the progression of root colonization by arbuscular mycorrhizal fungi (AMF), dark septate endophytes (DSE), and fine root endophytes (FRE) over an alpine growing season, and to understand the role of the host plant and environment in driving colonization levels. We sampled four forbs on a regular schedule from June 26th-September 11th from a moist meadow (3535m a.s.l) on Niwot Ridge, Rocky Mountain Front Range, CO, USA. We quantified the degree of root colonization by storage structures, exchange structures, and hyphae of all three groups of fungi. AMF and FRE percent colonization fluctuated significantly over time, while DSE did not. All AMF structures changed over time, and the degree of change in vesicles differed by plant species. FRE hyphae, AMF arbuscules and AMF vesicles peaked late in the season as plants produced seeds. AMF hyphae levels started high, decreased, and then increased within 20days, highlighting the dynamic nature of plant-fungal interactions. Overall, our results show that AMF and FRE, not DSE, root colonization rapidly changes over the course of a growing season and these changes are driven by plant phenology and seasonal changes in the environment.

Direct effects of soil cadmium on the growth and activity of arbuscular mycorrhizal fungi

A compartment cultivation system was developed to study the effect of cadmium (Cd) in soil on the development of arbuscular mycorrhizal fungi (AMF) under the same host conditions. Fungal compartments consisting of four levels of Cd addition rate (0, 5, 25 and 50 mg kg−1) were inserted into each porcelain pot in the greenhouse. Mycorrhizal development by Glaroideoglomus etunicatum and Glaroideoglomus claroideum was determined at three growth stages of Cucumis sativus. Both AMF isolates showed good root colonization during plant growth. Total extraradical mycelium (ERM) length and active ERM length reached a maximum at low Cd addition rate (5 mg kg−1) and were inhibited at the higher Cd addition rate (25 and 50 mg kg−1). The two AMF isolates showed different responses to Cd addition at the three growth stages and G. claroideum seemed to be more tolerant to Cd toxicity. These results showed a potential to use this technique to study the function of soil-grown AMF hyphae.

Arbuscular mycorrhizal fungi stimulate organic phosphate mobilization associated with changing bacterial community structure under field conditions

The extraradical hyphae of arbuscular mycorrhizal fungi (AMF) harbour and interact with a microbial community performing multiple functions. However, how the AMF-microbiome interaction influences the phosphorus (P) acquisition efficiency of the mycorrhizal pathway is unclear. Here we investigated whether AMF and their hyphal microbiome play a role in promoting organic phosphorus (P) mineralizing under field conditions. We developed an AMF hyphae in-growth core system for the field using PVC tubes sealed with membrane with different size of pores (30 or 0.45 μm) to allow or deny AMF hyphae access to a patch of organic P in root-free soil. AMF and their hyphae associated microbiome played a role in enhancing soil organic P mineralization in situ in the field, which was shown to be a function of the change in bacteria community on the hyphae surface. The bacterial communities attached to the AMF hyphae surface were significantly different from those in the bulk soil. Importantly, AMF hyphae recruited bacteria that produced alkaline phosphatase and provided a function that was absent from the hyphae. These results demonstrate the importance of understanding trophic interactions to be able to gain insight into the functional controls of nutrient cycles in the rhizosphere.

Abundance of rhizospheric bacteria and fungi associated with Fouquieria columnaris at Punta Cirio, Sonora, Mexico

A unique relictual population of Fouquieria columnaris is located in Sonora, along a 45-km strip of land encompassing Punta Cirio in the Sonoran Desert. The interaction of plants with microorganisms is an important adaptation to survival in desertic areas. The present study reports the abundance of bacteria, actinobacteria, and filamentous and arbuscular mycorrhizal fungi (AMF) in the rhizosphere of F. columnaris at Punta Cirio. Also, the genetic variability of F. columnaris was analyzed using amplied fragment length polymorphism markers. Bacteria and fungi in 27 soil samples from the rhizosphere of F. columnaris at 3 hills with low, medium, and high elevations were analyzed. The total bacterial, actinobacterial, and filamentous fungal counts did not differ among sites or elevations; no interaction between site and elevation was found. Nitrogen-fixing bacteria varied according to site but not elevation, whereas phosphorus-solubilizing bacteria were undetected. Filamentous fungi were dominated by Aspergillus spp. (48%) and Penicillium spp. (28%), which together represented 76% of the total average colony-forming units. The spore density of AMF ranged from 109 to 245 per 100 g of soil, and 65 to 80% of roots were colonized by hyphae, vesicles, or arbuscles of AMF. The DNA analysis generated an average similarity coefficient of 0.89, which could indicate high genetic homogeneity within the evaluated F. columnaris population.

Experimental disconnection from common mycorrhizal networks has little effect on competitive interactions among common temperate grassland species

Abstract The extent to which plants can reduce nutrient concentrations in soil and thereby compete with others may increase with nutrient mobility. Hyphae of arbuscular mycorrhizal fungi (AMF) can extend the soil volume from which plants acquire phosphorus (P), thus increasing competition for these resources with neighbours. In this study, we tested whether the suppression of hyphal interconnections between neighbour plants mitigates their competitive interactions and consequently affects plant community structure. We used custom‐built microcosms that used a wire system to suppress the development of a common mycorrhizal network (CMN) between plant neighbours. We applied this CMN treatment to plants without neighbours (competition‐free controls), with conspecific neighbours (monocultures) or with heterospecific neighbours (two and four species communities), all assembled from two pools of four separate temperate grassland species each. We analysed changes in species and community‐level productivity and P acquisition. The CMN treatment affected species differently. Most species had reduced shoot biomass while root biomass increased with CMN disconnection. Productivity and nutrient acquisition of Plantago lanceolata in four‐species mixtures was negatively affected, leading to a less even distribution of P among species, but community‐level P acquisition was not affected. On average, two‐species and four‐species mixtures produced similar community biomass and had the same P content as monocultures. Synthesis. Common mycorrhizal network disconnection affected competitive interactions among species only little. One explanation may be that the absence of pronounced competitive hierarchy among the species investigated led to relatively symmetric interactions among species that were stable with respects to additional common mycorrhizal network effects. Another explanation is that common mycorrhizal network effects are less important in natural soils with natural arbuscular mycorrhizal fungi communities than experiments with few arbuscular mycorrhizal fungi strains and often sterilized soils suggest.