Arbuscular Mycorrhizal Fungi Activity Research Articles

Arbuscular mycorrhizal fungi activity in Haplic Luvisol on the semi-arid region of Pernambuco Brazil

The use of microorganisms aiming to improve the availability of nutrients for plants is an important and necessary practice for agriculture. Thus, studies on the AMF occurrence in northeastern Brazil and efficiency tests using native plants in the region have been intensified in recent decades. Aiming determine the most probable number (MPN) of infective propagules in the area with native vegetation in the semi-arid region of Pernambuco, municipality of Sertânia, and quantify the soil protein related to easily extractable glomalin (SPREEG) and to total glomalin (SPRTG), experiments were conducted in a greenhouse. For this study 10 composite soil samples were collected, with points randomly defined. Samples were homogenized and analyzed for physical and chemical characteristics. Being used for immediate examination and preparation trap cultures (one three-month cycle of propagation) to AMF, using as host plants sorghum (Sorghum bicolor L. Moench), and peanut (Arachis hypogaea L.). For determining the MPN of infective propagules of AMF in Haplic Luvisols, soil inoculum samples were diluted in the proportions of 0, 1:10, 1: 100 and 1: 1000 (soil inoculum: diluent soil, v: v) with 5 repetitions each, having maize (Zea mays L.) as host plant. The direct count (DC) differed significantly from the indirect (IC) of AMF with averages of 961.3 and 517.4 glomerospores per 100g soil, respectively. The NMP of infective propagules of AMF propagules found was 23 cm-3 and SPREEG and SPRTG were approximately 0.46 and 0.26 mg glomalin g-1 aggregate, respectively.

Risk assessment of replacing conventional P fertilizers with biomass ash: Residual effects on plant yield, nutrition, cadmium accumulation and mycorrhizal status

Reutilizing biomass ashes in agriculture can substitute inputs of P from finite primary sources. However, recycling of ashes is disputed due to their content of toxic substances such as heavy metals. This study evaluates the potential risk of replacing easily soluble inorganic P fertilizer with P in biomass ashes in a barley crop grown on soil with adequate P status. Two contrasting doses of three different types of ashes were applied to an agricultural field with spring barley and compared to similar doses of triple-superphosphate fertilizer. In the second growing season after biomass ash application, grain, straw and root dry matter yield, and P and Cd uptake were determined. Resin-extractable P was measured in soil and the symbiotic arbuscular mycorrhizal fungal activity, colonization, and community composition were assessed. Crop yield was not affected by ash application, while P-uptake and mycorrhizal status were slightly enhanced with high ash applications. Changes to the mycorrhizal community composition were evident with high ash doses. Cadmium uptake in aboveground plant tissue was unaffected by ash treatments, but increased in roots with increasing doses. Consequently, we conclude that fertilization with biomass ashes can replace conventional fertilizers without risk to barley crops in the short term.

Effect of Inoculation with Arbuscular Mycorrhizal Fungi on Selected Spring Wheat Lines

<p class="sar-body"><span lang="EN-US">An experiment was performed in a completely randomized split-plot design using five lines of spring wheat (<em>Triticum aestivum </em>L.) (AW-774, AC Carberry, HY-162, Major and AAC Scotia) and two arbuscular mycorrhizal fungi (AMF) strains (<em>Rhizoglomus irregulare </em>and <em>Glomus cubense</em>). Two different inoculant forms (solid and liquid) for the <em>G. cubense</em> strain were evaluated. The main plot was AMF, and the subplot was spring wheat lines. Data on heading date, plant height, fresh, and dry biomass, yield, grain quality (chemical composition of the seeds, gluten, and sugar), root structure, and colonization by AMF were collected. The results show a positive effect of inoculation in comparison with the control treatment. The liquid and solid <em>G. cubense</em> inoculants provided better results than inoculation with <em>R.</em> <em>irregulare</em>. Fungus indicators were in agreement with root morphological parameters because of the effect induced by AMF activity. Yield increased significantly in the mycorrhizal treatments.</span></p>

Characterizing and handling different kinds of AM fungal spores in the rhizosphere.

Spores are important propagules as well as the most reliable species-distinguishing traits of arbuscular mycorrhizal (AM) fungi. During surveys of AM fungal communities, spore enumeration and spore identification are frequently conducted, but generally little attention is given to the age and viability of the spores. In this study, AM fungal spores in the rhizosphere were characterized as live or dead by vital staining and by performing a germination assay. A considerable proportion of the spores in the rhizosphere were dead despite their intact appearance. Furthermore, morphological and molecular analyses of spores to determine species identity revealed that both viable spores and dead spores with contents were identified. The accurate identification of spores at different developmental stages on the basis of morphology requires considerable experience. Our findings suggest that surveys of AM fungal communities based on spore enumeration and morphological and molecular identification are likely to be inaccurate, primarily because of the large proportion of dead spores in the rhizosphere. A viability check is recommended prior to spore molecular identification, and the use of trap cultures would give more reliable morphological identification results. We show that the abundance and activity of AM fungi in the rhizosphere can be determined by calculating the density of viable spores and the density of spores that could germinate. The adoption of these methods should provide a more reliable basis for further AM fungal community analysis.

Arbuscular mycorrhizal fungal activity responses to winter cover crops in a sunflower and maize cropping system

The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) benefits the health, nutrition and abiotic stress tolerance of the host plant. The maintenance of potential AMF inoculum in the winter is important because it will affect the colonization process in the subsequent crop. The objective of this study was to evaluate the effect of winter cover crops (CC) on AMF parameters (root colonization, length of hyphae and number of AMF spores), other variables indirectly related to AMF (the easily extractable glomalin-related soil protein (EE-GRSP) and the enzymatic activity of β-glucosaminidase), along with water-stable aggregates (WSA) as a soil quality indicator. In addition, the effect of two sampling dates on the variables in maize and the relationships among all of the variables were studied. The samples were obtained from a field experiment established in 2006 located in Aranjuez (Central Spain) under a Mediterranean semiarid climate. The treatments were winter cover crops of barley (Hordeum vulgare L.) or vetch (Vicia villosa L.) and fallow as a control. The study covered two seasons in 2011–12 and 2012–13 with sunflower (Helianthus annuus L.) and maize (Zea mays L.) as the main crop, respectively, with both sown in the spring. The main crops were irrigated according to the crop demand. Compared with the bare fallow conditions, cover crops improved most of the variables, maintaining the benefits of CC on AMF under the semiarid conditions of the Mediterranean climate. Barley as a cover crop gave the best results, whereas the performance of vetch was poorer. In sunflower, barley increased by 80% the hyphae length and β-glucosaminidase activity and by 30% other variables compared with the fallow; whereas in maize, 60–70% increments were found in AMF spores and the hyphae length and 2-fold in the enzyme activity. The sampling date affected all of the variables analyzed in the maize crop, except for the EE-GRSP and the WSA. Positive relationships were found between the variables directly related to AMF, EE-GRSP content and β-glucosaminidase activity. This suggests that the variables indirectly related to AMF, mainly the EE-GRSP, could be used as indicators of AMF. Finally, the enhancement of soil aggregate stability by the CC via AMF promotion was corroborated.

Can soil properties and agricultural land use affect arbuscular mycorrhizal fungal communities indigenous from the Argentinean Pampas soils?

In order to determine if intensive agricultural land use and/or edaphic characteristics modify the community of the arbuscular mycorrhizal fungi (AMF) indigenous of soils from the Argentinean Pampa; mycorrhizal colonization, sporulation, glomalin (GRSP) and genetic diversity were assessed. Soils were collected from seven localities from Buenos Aires Province (Argentina) under contrasting land use intensity (at each site both pristine and agricultural soils). The capacity for root colonization, sporulation and glomalin content of trap plants and growth substrate were considered as measure of AMF activity. Analysis of diversity was conducted using PCR-single strand conformation polymorphism (SSCP). Profiles were generated by using primers to amplify the 28S rDNA of AMF from rDNA extracted directly from the substrate of trap plant or AMF spore. Five bands of the SSCP gel were sequenced and showed similarity with the genus Glomus. Analysis of colonization and GRSP content, were not clearly related to the land use intensity but sporulation capacity was, in general, lower in agricultural soils than in pristine ones. Soil phosphorus, ferrum and zinc contents, were negatively related to the root colonization and sporulation capacities. High genetic diversity was found both from soil and spore samples. Although similar diversity was found under agricultural and pristine soils, in most sites SSCP-diversity was separately clustered by land use. Still remains clarify if soil characteristics, resulting from agricultural management; exert selection pressure on the AMF and whether they could be vectors of interest to select potential plant growth promoting microorganisms.

The molecular characteristics of compost affect plant growth, arbuscular mycorrhizal fungi, and soil microbial community composition

Compost amendment to agricultural soils influences plant growth and soil quality by affecting activity of arbuscular mycorrhizal fungi (AMF) and composition of microbial community. We related the molecular composition of compost of different maturity added to soils to their effects on maize growth, N and P uptake, AMF root colonization and growth, and composition of soil microbial community. The characteristics of compost after different days of maturation (C60, C90, C120) were provided by 13C-solid state NMR spectroscopy, while neutral (NLFA) and phospholipid (PLFA) fatty acid analyses were used to evaluate the effects of compost on the composition of soil microbial communities. Multivariate elaboration was used to determine the relationships between microbial groups, as identified by PLFA analysis, and molecular properties of composts. Although compost amendments increased soil total C and N, and available P, soil addition of both C60 and C120 compost samples was detrimental to plant and AMF growth. Compost amendments modified the composition of soil microbial communities. The high content of biolabile compounds in C60 and C120 compost samples decreased the C16:1ω5 NLFA that was related to AMF and Gram(+)/Gram(−) and AMF/saprotrophic fungi ratios. A linear correlation was found between the molecular indexes in compost and the microbial groups in soil, thereby suggesting that the molecular composition of compost strictly controls the development and abundance of soil microbial communities. These findings highlight the importance of controlling the molecular quality of recycled biomass added to soil, in order to predict the effect on crop yields and biotic composition of soil.

Effects of soil tillage and planting grass on arbuscular mycorrhizal fungal propagules and soil properties in citrus orchards in southeast China

Arbuscular mycorrhizal (AM) fungi play important roles in plant nutrition and soil conservation. AM fungal activity and amount of glomalin (a glycoprotein derived from AM fungi) are influenced by a series of abiotic and biotic factors associated with changes in soil management. However, the informations concerning AM fungal activity, amount of glomalin-related soil protein (GRSP), and its relationship with soil fertility and enzyme activities are scarce in citrus orchards under different soil management systems. Accordingly, this paper reports the effects of tilling soil and planting grass on AM colonization; AM fungal propagules; the amount of GRSP and its relationship with soil chemicals including organic carbon, available nitrogen, Olsen phosphorus, and available potassium; the activity levels of soil enzymes like catalase, invertase, urease, and acid phosphatase in citrus (Citrus unshiu Marc. grafted on Poncirus trifoliata L. Raf.) orchards in southeast China. Measurements were conducted in the fifth year of an ongoing tillage and grass planting experiment on an Acrisol soil under one of three treatments: natural grass cover, sod culture with white clover, and clean tillage. Soils and roots were sampled in March, July, and November 2013, during the vigorous growth period of citrus trees. AM colonization, AM fungal propagules, and GRSP were significantly higher in both no-tillage and grass-planted orchards than in clean tillage orchards. Soil organic carbon, available nitrogen, and soil enzyme activities showed a similar trend. Principal component analysis revealed that tillage and grass planting dramatically affected soil conditions in citrus orchards. However, sod culture promoted citrus mycorrhizal colonization and available nitrogen in soil more effectively than did grass cover, whereas natural grass cover enhanced AM fungal propagules, soil organic carbon, and soil enzyme activities more effectively than did sod culture. Soil organic carbon, available nitrogen, and soil enzymes activities were significantly (P<0.05) correlated with AM fungal propagules or GRSP, suggesting that plentiful AM symbionts may help preserve soil quality, especially in grass-planted orchards.

Effects of Preconditioning Through Mycorrhizal Inoculation on the Control of Melon Root Rot and Vine Decline Caused by Monosporascus cannonballus

AbstractThe use of inoculum of arbuscular mycorrhizal fungi (AMF) in nursery represents a promising field in horticulture because of its known benefits in terms of plant growth and bioprotection. The present work was undertaken to determine the effect of mycorrhizal inoculation with Rhizophagus irregularis in a nursery medium on the containment of melon root rot and vine decline (MRRVD) caused by the soil‐borne pathogen Monosporascus cannonballus. The percentage of mycorrhization, biomass and yield following mycorrhizal inoculation were also evaluated. Biocontrol activity was assessed in greenhouse pot experiments upon artificial inoculation of M. cannonballus and in a two‐season field experiment under production conditions in an unheated greenhouse with a history of MRRVD. On the basis of the mycorrhization parameters, the interaction appeared to be established within 30 days after inoculation. The total shoot growth in the mycorrhized plants was significantly higher when compared to the control, while the root growth was unaffected. Upon artificial inoculation of M. cannonballus, mycorrhization provided complete protection against the pathogen. Greenhouse experiments under production conditions during spring cropping season showed that pretransplanting inoculation with R. irregularis significantly decreased the severity of the disease. Also, the average fruit weight of mycorrhized plants was significantly higher than the untreated control. Nevertheless, in summer crop, the bioprotection activity of AMF failed. Present results indicate that the use of AMF in a nursery setting can contribute to the prevention of the onset of this problematic soil‐borne disease within a sustainable and integrated soil‐borne disease management.

Relative abundance of and composition within fungal orders differ between cheatgrass (Bromus tectorum) and sagebrush (Artemisia tridentata)-associated soils.

Nonnative Bromus tectorum (cheatgrass) is decimating sagebrush steppe, one of the largest ecosystems in the Western United States, and is causing regional-scale shifts in the predominant plant-fungal interactions. Sagebrush, a native perennial, hosts arbuscular mycorrhizal fungi (AMF), whereas cheatgrass, a winter annual, is a relatively poor host of AMF. This shift is likely intertwined with decreased carbon (C)-sequestration in cheatgrass-invaded soils and alterations in overall soil fungal community composition and structure, but the latter remain unresolved. We examined soil fungal communities using high throughput amplicon sequencing (ribosomal large subunit gene) in the 0-4 cm and 4-8 cm depth intervals of six cores from cheatgrass- and six cores from sagebrush-dominated soils. Sagebrush core surfaces (0-4 cm) contained higher nitrogen and total C than cheatgrass core surfaces; these differences mirrored the presence of glomalin related soil proteins (GRSP), which has been associated with AMF activity and increased C-sequestration. Fungal richness was not significantly affected by vegetation type, depth or an interaction of the two factors. However, the relative abundance of seven taxonomic orders was significantly affected by vegetation type or the interaction between vegetation type and depth. Teloschistales, Spizellomycetales, Pezizales and Cantharellales were more abundant in sagebrush libraries and contain mycorrhizal, lichenized and basal lineages of fungi. Only two orders (Coniochaetales and Sordariales), which contain numerous economically important pathogens and opportunistic saprotrophs, were more abundant in cheatgrass libraries. Pleosporales, Agaricales, Helotiales and Hypocreales were most abundant across all libraries, but the number of genera detected within these orders was as much as 29 times lower in cheatgrass relative to sagebrush libraries. These compositional differences between fungal communities associated with cheatgrass- and sagebrush-dominated soils warrant future research to examine soil fungal community composition across more sites and time points as well as in association with native grass species that also occupy cheatgrass-invaded ecosystems.

Relative abundance of and composition within fungal orders differ between cheatgrass (Bromus tectorum) and sagebrush (Artemisia tridentate)-associated soils.

Nonnative Bromus tectorum (cheatgrass) is decimating sagebrush steppe, one of the largest ecosystems in the Western United States, and is causing regional-scale shifts in the predominant plant-fungal interactions. Sagebrush, a native perennial, hosts arbuscular mycorrhizal fungi (AMF), whereas cheatgrass, a winter annual, is a relatively poor host of AMF. This shift is likely intertwined with decreased carbon (C)-sequestration in cheatgrass-invaded soils and alterations in overall soil fungal community composition and structure, but the latter remain unresolved. We examined soil fungal communities using high throughput amplicon sequencing (ribosomal large subunit gene) in the 0–4 cm and 4–8 cm depth intervals of six cores from cheatgrass- and six cores from sagebrush-dominated soils. Sagebrush core surfaces (0–4 cm) contained higher nitrogen and total C than cheatgrass core surfaces; these differences mirrored the presence of glomalin related soil proteins (GRSP), which has been associated with AMF activity and increased C-sequestration. Fungal richness was not significantly affected by vegetation type, depth or an interaction of the two factors. However, the relative abundance of seven taxonomic orders was significantly affected by vegetation type or the interaction between vegetation type and depth. Teloschistales, Spizellomycetales, Pezizales and Cantharellales were more abundant in sagebrush libraries and contain mycorrhizal, lichenized and basal lineages of fungi. Only two orders (Coniochaetales and Sordariales), which contain numerous economically important pathogens and opportunistic saprotrophs, were more abundant in cheatgrass libraries. Pleosporales, Agaricales, Helotiales and Hypocreales were most abundant across all libraries, but the number of genera detected within these orders was as much as 29 times lower in cheatgrass relative to sagebrush libraries. These compositional differences between fungal communities associated with cheatgrass- and sagebrush-dominated soils warrant future research to examine soil fungal community composition across more sites and time points as well as in association with native grass species that also occupy cheatgrass- invaded ecosystems.

Diverse bacterial communities are recruited on spores of different arbuscular mycorrhizal fungal isolates

Arbuscular mycorrhizal fungi (AMF) establish mutualistic symbioses with the roots of most food crops, playing a key role in soil fertility and plant nutrition and health. The beneficial activity of AMF may be positively affected by bacterial communities living associated with mycorrhizal roots, spores and extraradical hyphae. Here, we investigated the diversity of bacterial communities associated with the spores of six AMF isolates, belonging to different genera and species and maintained for several generations in pot cultures with the same host plant, under the same environmental conditions and with the same soil. The occurrence of large bacterial communities intimately associated with spores of the AMF isolates was revealed by PCR denaturing gradient gel electrophoresis (DGGE) analysis and sequencing of DGGE bands. Cluster and canonical correspondence analysis showed that the six AMF isolates displayed diverse bacterial community profiles unrelated with their taxonomic position, suggesting that each AMF isolate recruits on its spores a different microbiota. The 48 sequenced fragments were affiliated with Actinomycetales, Bacillales, Pseudomonadales, Burkholderiales, Rhizobiales and with Mollicutes-related endobacteria (Mre). For the first time, we report the occurrence of Mre in Funneliformis coronatum and Rhizophagus intraradices and sequences related to endobacteria of Mortierella elongata in F. coronatum and Funneliformis mosseae. The bacterial species identified are known to possess diverse and specific physiological characteristics and may play multifunctional roles affecting the differential performance of AMF isolates, in terms of infectivity and efficiency.

Impact of arbuscular mycorrhizal fungi (AMF) on cucumber growth and phosphorus uptake under cold stress.

Symbiosis with root-associated arbuscular mycorrhizal fungi (AMF) can improve plant phosphorus (P) uptake and alleviate environmental stresses. It could be also an effective mean to promote plant performance under low temperatures. The combined effects of arbuscular mycorrhiza and low temperature (15°C/10°C day/night) on cucumber seedlings were investigated in the present study. Root colonisation by AMF, succinate dehydrogenase and alkaline phosphatase activity in the intraradical fungal structures, plant growth parameters, and expression profiles of four cucumber phosphate (Pi) transporters, the fungal Pi transporter GintPT and alkaline phosphatase GintALP were determined. Cold stress reduced plant growth and mycorrhizal colonisation. Inoculation improved cucumber growth under ambient temperatures, whereas under cold stress only root biomass was significantly increased by inoculation. AMF supplied P to the host plant under ambient temperatures and cold stress, as evidenced by the higher P content of mycorrhizal plants compared with non-mycorrhizal plants. Thus, the cold-stressed cucumber seedlings still benefited from mycorrhiza, although the benefit was less than that under ambient temperatures. In accordance with this, a cucumber Pi transporter gene belonging to the Pht1 gene family was strongly induced by mycorrhiza at ambient temperature and to a lesser extent under cold stress. The other three Pi transporters tested from different families were most highly expressed in cold-stressed mycorrhizal plants, suggesting a complex interactive effect of mycorrhiza and cold stress on internal P cycling in cucumber plants.

Rotation of hyphal in-growth cores has no confounding effects on soil abiotic properties

To disentangle effects of fungal hyphae and plant roots hyphal in-growth cores have become a common tool in research on arbuscular mycorrhizal fungi (AMF). However, it is unknown if the frequent rotation of a compartment has any side-effects that may hinder attributing findings to AMF. We set up an experiment with the presence/absence of a non-AMF microbial community, where each pot contained a rotated and a non-rotated soil core. The results show that within our rotation design soil parameters such as water content, soil structure, pH, and C and N concentrations are not influenced by the regular rotation in the absence of AMF. Our study therefore clearly underlines the validity of the rotated hyphal in-growth core as an experimental control for AMF growth and activity.

Interactive effects of arbuscular mycorrhizal fungi and intercropping with sesame (Sesamum indicum) on the glucosinolate profile in broccoli (Brassica oleracea var. Italica)

This study determined interactive effects of arbuscular mycorrhizal (AM) fungi and sesame (Sesamum indicum) intercropping on glucosinolate concentrations in broccoli (Brassica oleracea var. Italica) plants. An experimental intercropping model of a horizontal three-compartment split-root system was used. It comprised the middle (combi) compartment shared by one part of the root system of the two intercropped plants, and two outer (solo) compartments with the other part of each root system. Broccoli was intercropped either with an AM host plant (sesame) or an AM non-host plant (broccoli). All intercropping combinations were cultivated in soil that was either mycorrhiza free [−M] or inoculated with Rhizophagusirregularies [+M]. Although broccoli roots were not internally colonised by mycorrhiza, AM inoculation of broccoli intercropped with sesame induced a systemic increase of indole glucosinolates in broccoli roots and leaves. This increase differed in the individual indole glucosinolate: in particular, 3-indolylmethyl glucosinolate was enhanced in leaves and its methoxylated derivative 4-methoxy-3-indolylmethyl glucosinolate was raised in roots. These interactive effects suggest that the activity of AM fungi in the (combi) compartment was stimulated by the AM host plant sesame, leading to a persistent invasion of AM fungi of the broccoli root surface. This may lead to a constant defence response in broccoli. The broccoli biomass was not negatively affected by AM fungal inoculation. When intercropped with sesame, the dry matter of broccoli shoots was increased.

Changes of arbuscular mycorrhizal traits and community structure with respect to soil salinity in a coastal reclamation land

A comprehensive knowledge on the relationship between soil salinity and arbuscular mycorrhizal fungi (AMF) is vital for a deeper understanding of ecosystem functioning under salt stress conditions. The objective of this study was to determine the effects of soil salinity on AMF root colonization, spore count, glomalin related soil protein (GRSP) and community structure in Saemangeum reclaimed land, South Korea. Soil samples were collected and grouped into five distinct salt classes based on the electrical conductivity of soil saturation extracts (ECse). Mycorrhizal root colonization, spore count and GRSP were measured under different salinity levels. AMF community structure was studied through three complementary methods; spore morphology, terminal restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis (DGGE). Results revealed that root colonization (P < 0.01), spore count (P < 0.01) and GRSP (P < 0.01) were affected negatively by soil salinity. Spore morphology and T-RFLP data showed predominance of AMF genus Glomus in Saemangeum reclaimed land. T-RFLP and DGGE analysis revealed significant changes in diversity indices between non (ECse < 2 dS/m) and extremely (ECse > 16 dS/m) saline soil and confirmed dominance of Glomus caledonium only in soils with ECse < 8 dS/m. However, ribotypes of Glomus mosseae and Glomus proliferum were ubiquitous in all salt classes. Combining spore morphology, T-RFLP and DGGE analysis, we could show a pronounced effect in AMF community across salt classes. The result of this study improve our understanding on AMF activity and dominant species present in different salt classes and will substantially expand our knowledge on AMF diversity in reclaimed lands.

Glomalin Production and Infectivity of Arbuscular-Mycorrhizal Fungi in Response to Grassland Plant Diversity

Arbuscular-mycorrhizal fungi (AMF) are integral components of most terrestrial ecosystems, with complex interactions between plants and AMF. Our study assessed the impact of plant diversity of native grassland species on AMF infectivity and production of glomalin, an AMF hyphal glycoprotein that may play an important role in soil aggregation. The study was conducted over a 3-year period in field plots planted with 1, 2, 8, or 16 plant species. The mycorrhizal infection potential (MIP) of the plots was assayed in the greenhouse. Glomalin production and MIP were lowest in monocultures and were more closely correlated with plant diversity than with plant cover. Spore density was also greater in higher diversity plots. Lower AMF activity in monoculture plots may contribute to lower productivity and soil quality in plant monocultures. Immunoreactive glomalin levels varied seasonally, with higher levels in late summer than in late spring. Positive correlations were found between glomalin levels and spore density, and between MIP and spore density, but not between MIP and glomalin.

Arbuscular mycorrhizal fungi in a semi-arid, limestone mining-impacted area of Brazil

The main goal of this study was to determine the diversity and activity of arbuscular mycorrhizal fungi (AMF) in an area degraded by limestone mining within the semi-arid region of Brazil known as the caatinga (shrublands). Near a limestone quarry, we selected two areas of caatinga (preserved and degraded) for study. The number of glomerospores did not differ significantly between the two areas. There was a trend toward the most probable number of infective propagules being higher in the degraded area. Twenty AMF taxa were identified in the two sampled areas, species richness, diversity and evenness being higher in the preserved area. Two species of Racocetra represent new records for the semi-arid region of Brazil. Glomerospore production and AMF species richness were unaffected by mining activity in the study area.

Native maize landraces from Los Tuxtlas, Mexico show varying mycorrhizal dependency for P uptake

Different degrees of dependency on the activity of arbuscular mycorrhizal fungi (AMF) exist between native maize landraces and hybrids. In Los Tuxtlas, Mexico, the Popoluca people maintain a traditional polycultural land management with more than 15 native landraces of maize; however, it is not known whether the recent substitution of local maize for improved hybrids and fertilization has affected the integrity of the mycorrhizal symbiosis in these naturally phosphorus-poor systems. A greenhouse experiment was conducted to evaluate the response of four Popoluca maize landraces and the hybrid Texcoco to the presence of native AMF in conditions of low and medium P input (5 and 65 mg kg−1, respectively). After 120 days in both P treatments, the native landraces Black and Yellow presented higher colonization and had acquired more P in their shoot biomass than the hybrid. The moderate fertilization did not appear to have affected the integrity of the mycorrhizal symbiosis, since all of the maize types presented a positive mycorrhizal dependency (2–14 %). Under low P conditions, the Texcoco hybrid maize presented one of the highest mycorrhizal dependencies; however, unlike the local landraces, this was not reflected in a higher tissue P concentration. The results obtained indicate that the native maize Black was the best at capturing symbiotic and direct P, which makes this landrace an important genetic and cultural heritage for the Popoluca and for the world.

Mycorrhizal activity and diversity in a long-term organic Mediterranean agroecosystem

In organic agriculture, soil fertility and productivity rely on biological processes carried out by soil microbes, which represent the key elements of agroecosystem functioning. Arbuscular mycorrhizal fungi (AMF), fundamental microorganisms for soil fertility, plant nutrition and health, may play an important role in organic agriculture by compensating for the reduced use of fertilizers and pesticides. Though, AMF activity and diversity following conversion from conventional to organic farming are poorly investigated. Here we studied AMF abundance, diversity and activity in short- and long-term organically and conventionally managed Mediterranean arable agroecosystems. Our results show that both AMF population activity, as assessed by the mycorrhizal inoculum potential (MIP) assay, the percentage of colonized root length of the field crop (maize) and glomalin-related soil protein (GRSP) content were higher in organically managed fields and increased with time since transition to organic farming. Here, we showed an increase of GRSP content in arable organic systems and a strong correlation with soil MIP values. The analysis of AMF spores showed differences among communities of the three microagroecosystems in terms of species richness and composition as suggested by a multivariate analysis. All our data indicate that AMF respond positively to the transition to organic farming by a progressive enhancement of their activity that seems independent from the species richness of the AMF communities. Our study contributes to the understanding of the effects of agricultural managements on AMF, which represent a promising tool for the implementation of sustainable agriculture.