Arbuscular Mycorrhizal Fungi Propagules Research Articles

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.

Water availability and formation of propagules of arbuscular mycorrhizal fungi associated with sorghum

Arbuscular mycorrhizal fungi (AMF) promote greater tolerance to the negative effects of water stress in their host plants, yet may also be influenced by the availability of water in the production of their infective propagules. The objective of this study was to assess the effect of water availability in the soil on the sporulation of Claroideoglomus etunicatum, Gigaspora albida and Scutellospora heterogama, and the influence of this condition on the infective potential and number of nuclei in glomerospores of these species. The reduction of water availability from 75 to 25% did not decrease significantly the sporulation of C. etunicatum, but resulted in decrease of sporulation of G. albida (600 to 7 glomerospores per 30g−1 soil) and S. heterogama (274 to 2 glomerospores per 30g−1 soil). The water availability at 75 and 71% promoted maximum sporulation of G. albida and S. heterogama, respectively. While G. albida and S. heterogama had greater sporulation than C. etunicatum, the infective potential of these species was lower, which may be related to the life-strategy and type of infective propagules of each species. The number of nuclei per glomerospore varied only among the species (p<0.05), with C. etunicatum and G. albida presenting the higher number of nuclei when compared to S. heterogama, but no differences were found among the treatments of water availability (p>0.05). These results suggest that AMF have distinct sporulation strategies and the amount of glomerospores is not directly related to the infectivity of the inoculum. Possibly, the differences in the life-strategies among the species were greater than the effects of water availability.

The effect of arbuscular mycorrhiza fungal propagules on the growth of subterranean clover (Trifolium subterraneum L.) under Mn toxicity in ex situ experiments

AbstractThe role of intact extraradical mycelium (ERM) as the most effective fungal propagule in the formation of the tripartite symbiosis between indigenous arbuscular mycorrhizal fungi (AMF), rhizobia and subterranean clover was investigated under conditions of Mn toxicity. ERM was previously developed in 8 L pots under greenhouse conditions by growing plants, which exhibited various levels of mycotrophicity and were tolerant to the levels of Mn in the soil used in the experiment (Silene gallica L, Lolium rigidum L, Ornithopus compressus L. and Rumex bucephalophorus L). Contrasting conditions of the integrity of the ERM at the planting of subterranean clover were created by soil disturbance (ERM fragmented – soil disturbed; ERM intact – soil undisturbed). Where an intact ERM was present at the time of planting, growth of subterranean clover was 2.5 times greater after 21 days and 3.9 times after 42 days relative to other forms of AMF propagule. This enhanced growth was associated with a reduction in the Mn concentration of roots due to a greater AMF colonization at 21 days after planting. The protection granted by an enhanced AMF root colonization allowed a greater root nodule development, leading to more N acquisition and plant growth. The ERM can be developed in the soil by mycotrophic plants tolerant to the stressing agent and kept intact at the seeding of the crop to be protected by adopting appropriate tillage techniques.

Soil microbial community resilience with tree thinning in a 40-year-old experimental ponderosa pine forest

Establishment of native grasses is a primary objective of restoration in Pinus ponderosa var. scopulorum (P. & C. Lawson) forests in the southwestern United States. Interactions among native grasses and soil microorganisms generate feedbacks that influence the achievement of this objective. We examined soil chemical properties and communities of plants and soil microorganisms in clear-cuts and P. ponderosa stands thinned and maintained at low and medium tree densities for over 40 years along with high density (unthinned) stands. Phospholipid fatty acids (PLFA) in soils were analyzed to examine arbuscular mycorrhizal (AM) fungi and microbial communities in the three thinning treatments and the unthinned stands with and without a recent broadcast burn. Additionally, two native bunchgrasses, Festuca arizonica and Muhlenbergia wrightii were grown in containers filled with intact soil cores collected from each field plot to more thoroughly compare the abundance of AM fungi and microbial communities across different stand densities and burn treatments. Tree thinning decreased litter cover and increased the abundance and diversity and altered community composition of both herbaceous vegetation and AM fungi. In the mineral soil layer, the pH, total carbon, nitrogen, phosphorus and PLFA profiles did not differ significantly among the four stand density or burn treatments. Mycorrhizal colonization of the container grown grasses did not significantly differ with tree density or burn treatments; however, F. arizonica roots had a strong trend for decreased colonization when grown in soil from high density (unthinned) tree cover. Soil from the containers with F. arizonica had a greater abundance of AM fungal spores. Furthermore, bacterial community composition varied with grass species. Concentration of biomarkers for bacteria were higher in soil that supported F. arizonica compared to soil in which M. wrightii was grown. Our results indicate that the creation of clear-cut openings in forests may increase the abundance and richness of AM fungal propagules and soil bacterial communities were surprisingly resilient to tree thinning and low-intensity fire treatments. These results suggest managing forests to create clear-cut openings generate conditions that favor understory native grasses and AM fungi that are linked to soil bacterial communities.

Arbuscular mycorrhizal fungi positively affect growth of Ailanthus altissima (Mill.) Swingle seedlings and show a strong association with this invasive species in Mediterranean woodlands

Arbuscular mycorrhizal fungi (AMF) may promote plant invasion by enhancing plant performance and competitiveness. However, only a small number of studies have considered the interactions between local soil microbial communities and invasive plants, and even fewer have focused on alien trees. Ailanthus altissima (Mill.) Swingle is a serious problem in the Mediterranean Basin, where it has invaded many habitats. We investigated the symbiosis between A. altissima and indigenous AMF in two invaded, ecologically different Mediterranean woodlands. Mycorrhizal infection was high at both sites (> 60% of the root fragments were mycorrhizal), indicating that A. altissima roots may be infected by AMF under different ecological conditions. In a greenhouse experiment, A. altissima seedling growth was evaluated in untreated soil (natural soil containing the entire microbial community except AMF propagules), in sterilized soil, and in sterilized soil containing the entire microbial community except AMF. Seedling growth was greater in the natural soil than in the other two soils. Seedlings in natural soil but not in the other two soils were extensively colonized by AMF, indicating that AMF may have been responsible for the greater growth in the natural soil. Growth was poorer in the sterile soil that had been inoculated with a soil suspension lacking AMF propagules than in the sterile soil, suggesting that the natural soil also contained pathogens and that the AMF countered the effects of these pathogens. Overall, the results indicate that AMF are an important biotic component of Mediterranean woodlands invaded by A. altissima and AMF may facilitate A. altissima's invasion in these woodlands.

Contrasting effects of long-term fertilization on the community of saprotrophic fungi and arbuscular mycorrhizal fungi in a sandy loam soil

The changes of saprotrophic fungi (SF) and symbiotic arbuscular mycorrhizal fungi (AMF) in response to different fertilizers were investigated in a period of 21 years. Denaturing gradient gel electrophoresis profiles showed fungal community structure significantly changed after long-term fertilization. Long-term organic and mineral fertiliza tion significantly increased the SF diversity, whereas mineral fertilization decreased the AMF diversity. SF quan tity significantly increased in response to organic fertilizers, whereas the AMF propagules were down-regulated by nutrient-rich fertilization but induced by N, P or K-deficiency. Redundancy analysis showed that long-term fertilization differentially affected diversity and quantity of SF and AMF. Nutrient-rich organic fertilizers, resulting in higher contents of soil organic C (SOC), total N and mineral N, total and available P, regulated the quantity and diversity of SF positively and quantity of AMF negatively, respectively. The diversity of AMF was slightly downregulated by SOC, total and mineral N and total P as well as the nutrient-rich mineral treatments, in contrast to the positive effects by available K and P. These results indicate that soil nutritional status and fertilizer types signifi cantly affect SF and AMF. Our study of soil fungal community in response to the long-term fertilization can provide new strategies for agronomic practice.

Effect of Soil Solarization on Native AM Fungi and Microbial Biomass

An experiment was conducted to study the effect of soil solarization on native arbuscular mycorrhizal (AM) fungi and soil microbial biomass. Solarization was done using transparent polyethylene (TPE) sheets of 0.05 and 0.10 mm thickness for 20, 40, and 60 days. Sunflower crop was taken after solarization. In plots solarized with 0.05 mm TPE sheets, soils solarized for 60 days had lesser number of infective propagules of AM fungi compared to those solarized for 40 or 20 days. However in soils solarized with TPE sheets of 0.10 mm thickness, no significant difference in spore numbers was found. Mycorrhizal colonization was significantly less in solarized soils, except in soils solarized with 0.10 mm TPE for 60 days. Soil microbial biomass increased as solarization period increased from 20 to 60 days in plots solarized with both 0.05 and 0.10 mm TPE. The yield of sunflower was significantly more in plots solarized for 60 days with TPE sheets of 0.05 or 0.10 mm thickness. There was a significant positive correlation between soil microbial biomass and seed yield. Though not significantly, soil microbial biomass and AM colonization were positively correlated, suggesting that mycorrhizal colonization might be stimulating soil microbial biomass. Therefore, even though microbial biomass correlated significantly with seed yield (r = +0.677*), the increase in seed yield could be attributed to an interaction effect of both AM colonization, and soil microbial biomass. This is the first report bringing out the various factors like solarization, AM colonization and soil microbial biomass on seed yield of sunflower.

Below ground microbial diversity as influenced by coffee agroforestry systems in the Western Ghats, India

Soil microorganisms viz. bacteria, fungi, actinomycetes and arbuscular mycorrhizal (AM) fungi present in different typologies of coffee production systems were compared. In this study, two types of coffee plants, namely Arabica and Robusta, were grown under different agroforestry management such as coffee under one specialized shade species, multi-story coffee systems with 2 shade tree species, and coffee with 3 or more tree species under moist deciduous and evergreen ecological conditions. Samples were collected from 36 points to include different coffee ecosystems. The highest number of infective propagules of AM fungi was encountered in Arabica coffee under evergreen conditions. Population of bacteria, fungi and actinomycetes were higher under evergreen ecosystem compared to that of deciduous conditions. The population of nitrogen fixing bacteria was more than double in evergreen conditions compared to deciduous ecosystem. Number of lignin decomposing bacteria was higher in evergreen compared to deciduous conditions, but starch hydrolyzing bacteria and pectin-utilizing bacteria were more in deciduous ecosystem. Actinomycetes DAT2-1 isolated from deciduous ecosystem showed antagonistic activity against the root pathogen Fusarium chlamydosporum. It can be concluded that evergreen coffee system supports higher population of microorganisms. Of the two species of coffee, Arabica harboured more AM fungi, bacterial population, N fixers, P solubilizers and cellulose decomposing organisms while Robusta harboured higher number of fungi and actinomycetes. Of the three typologies, coffee grown under two shade tree species supported higher population of all microorganisms.

Role of arbuscular mycorrhizal symbiosis in phosphorus-uptake efficiency and aluminium tolerance in barley growing in acid soils

Arbuscular mycorrhizal fungi (AMF) play an important role in protecting plant growth against such stresses as phytotoxic aluminium (Al) in soil. To understand some of the AMF interactions that relate to amelioration of Al phytotoxicity and phosphorus (P)-uptake efficiency in barley (Hordeum vulgare L.), this study examined the effect of soil Al levels and mycorrhizal symbiosis on plant response, including root colonisation, AMF propagules and glomalin production. A greenhouse experiment was conducted using two native barley cultivars, Sebastián and Aurora, grown in an acidic soil at two Al-saturation levels (80% Al-sat, unlimed soil; 7% Al-sat, limed soil) with and without AMF propagules. Root dry weight, total and colonised root lengths, and root P and Al contents were determined at 60 and 150 days after sowing. AMF spore density, total hyphal length, glomalin-related soil protein (GRSP) and Al bound to GRSP (Al-GRSP) were analysed at final harvest. AM root colonisation was not inhibited in limed soil, mycorrhizal propagule numbers increased at high Al levels, and Al-GRSP ranged from 5.6% to 8.3% of the total GRSP weight. These values also increased in unlimed soil, particularly those associated with cv. Aurora. Root Al concentration correlated inversely with AMF spores (r = –0.85, P &lt; 0.001) and Al-GRSP (r = –0.72, P &lt; 0.01), but only in plants growing in limed soil. Conversely, the AMF treatments in which Al was present showed a greater relationship between total root length and both root Al (r = –0.72, P &lt; 0.01) and root P (r = 0.66, P &lt; 0.01) concentrations. Sebastián showed a greater response to lime, whereas Aurora responded better to mycorrhizal presence. The relative growth rate of roots, P uptake efficiency and mycorrhizal parameters such as root colonisation, spores, hyphae and GRSP showed Aurora to be more Al-tolerant than Sebastián. In conclusion, the greater rate of increase of AM propagules, GRSP and Al-GRSP associated with cv. Aurora supports the hypothesis that AMF play an important role in the Al-tolerance capacity and P-uptake efficiency of H. vulgare growing in soils with high Al levels.

Mass Production Techniques of Arbuscular Mycorrhizal Fungi: Major Advantages and Disadvantages: A Review

Numerous techniques have been developed in the past few decades for the mass production of arbuscular mycorrhizal (AM) fungi. The main obstacle behind the mass production techniques of AM fungi is the obligate nature of this biotrophic fungus and species level identification of AM fungal species could not be possible at the early stage of development. Currently, in-vitro cultivation methods such as hydroponic system and root organ culture has been widely used for the mass production of AM fungi. These methods are not only maintain the quality of AM fungal propagules but they can also be developed as cost effective methods for the mass propagation of AM fungi. The aim of this paper is to highlight the recent and advanced methods used for the mass production of AM fungi.

Colonization of green roof plants by mycorrhizal and root endophytic fungi

Green roof plants must survive hot and dry conditions in low nutrient artificial growing media. Although soil microorganisms such as arbuscular mycorrhizal fungi (AMF) can ameliorate these constraints by increasing water and mineral uptake, virtually nothing is known about the microbes associated with the roots of green roof plants. We determined levels of AMF and dark septate endophyte (DSE) colonization of plants grown for four years on an experimental green roof in Halifax, Nova Scotia. Green roof plant species included the forb Solidago bicolor, the grasses Danthonia spicata and Poa compressa and the succulent Sedum acre. We also assessed root colonization of these same species, as well as three additional succulents (Sedum spurium, Rhodiola rosea and Hylotelephium telephium), collected from their natural habitats. We further assessed the inoculum potential of a commercial green roof substrate before and after the introduction of host plants. Levels of AMF colonization were similar within plant species, regardless of collecting location (roof or field). All plant species were colonized except for the succulent S. acre, which is commonly utilized as a green roof plant. The commercial growing medium contained extremely low levels of viable AMF propagules, but this increased significantly after planting with Solidago. Conversely, all species (from roof, field and bioassay) were well colonized by DSE, which appear to differ from the AMF with respect to their pattern of dispersal onto the green roof. Although the widespread use of non-mycorrhizal succulent species such as S. acre precludes the ecosystem services provided by the AMF symbiosis, the benefits of both succulent tissue and AMF could be obtained simultaneously with careful green roof plant selection.

Bacteria associated with arbuscular mycorrhizal fungi within roots of plants growing in a soil highly contaminated with aliphatic and aromatic petroleum hydrocarbons.

Arbuscular mycorrhizal fungi (AMF) belong to phylum Glomeromycota, an early divergent fungal lineage forming symbiosis with plant roots. Many reports have documented that bacteria are intimately associated with AMF mycelia in the soil. However, the role of these bacteria remains unclear and their diversity within intraradical AMF structures has yet to be explored. We aim to assess the bacterial communities associated within intraradical propagules (vesicles and intraradical spores) harvested from roots of plant growing in the sediments of an extremely petroleum hydrocarbon-polluted basin. Solidago rugosa roots were sampled, surface-sterilized, and microdissected. Eleven propagules were randomly collected and individually subjected to whole-genome amplification, followed by PCRs, cloning, and sequencing targeting fungal and bacterial rDNA. Ribotyping of the 11 propagules showed that at least five different AMF OTUs could be present in S. rugosa roots, while 16S rRNA ribotyping of six of the 11 different propagules showed a surprisingly high bacterial richness associated with the AMF within plant roots. Most dominant bacterial OTUs belonged to Sphingomonas sp., Pseudomonas sp., Massilia sp., and Methylobacterium sp. This study provides the first evidence of the bacterial diversity associated with AMF propagules within the roots of plants growing in extremely petroleum hydrocarbon-polluted conditions.

Glyphosate herbicide affects belowground interactions between earthworms and symbiotic mycorrhizal fungi in a model ecosystem.

Herbicides containing glyphosate are widely used in agriculture and private gardens, however, surprisingly little is known on potential side effects on non-target soil organisms. In a greenhouse experiment with white clover we investigated, to what extent a globally-used glyphosate herbicide affects interactions between essential soil organisms such as earthworms and arbuscular mycorrhizal fungi (AMF). We found that herbicides significantly decreased root mycorrhization, soil AMF spore biomass, vesicles and propagules. Herbicide application and earthworms increased soil hyphal biomass and tended to reduce soil water infiltration after a simulated heavy rainfall. Herbicide application in interaction with AMF led to slightly heavier but less active earthworms. Leaching of glyphosate after a simulated rainfall was substantial and altered by earthworms and AMF. These sizeable changes provide impetus for more general attention to side-effects of glyphosate-based herbicides on key soil organisms and their associated ecosystem services.

Cultured arbuscular mycorrhizal fungi and native soil inocula improve seedling development of two pioneer trees in the Andean region

The tree species Alnus acuminata and Morella pubescens, native to South America, are candidates for soil quality improvement and afforestation of degraded areas and may serve as nurse trees for later inter-planting of other trees, including native crop trees. Both species not only form symbioses with arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF), but also with N2-fixing actinobacteria. Because tree seedlings inoculated with appropriate mycorrhizal fungi in the nursery resist transplanting stress better than non-mycorrhizal seedlings, we evaluated for A. acuminata and M. pubescens the potential of inoculation with mycorrhizal fungi for obtaining robust tree seedlings. For the first time, a laboratory-produced mixed AMF inoculum was tested in comparison with native soil from stands of both tree species, which contains AMF and EMF. Seedlings of both tree species reacted positively to both types of inocula and showed an increase in height, root collar diameter and above- and belowground biomass production, although mycorrhizal root colonization was rather low in M. pubescens. After 6 months, biomass was significantly higher for all mycorrhizal treatments when compared to control treatments, whereas aboveground biomass was approximately doubled for most treatments. To test whether mycorrhiza formation positively influences plant performance under reduced water supply the experiment was conducted under two irrigation regimes. There was no strong response to different levels of watering. Overall, application of native soil inoculum improved growth most. It contained sufficient AMF propagules but potentially also other soil microorganisms that synergistically enhance plant growth performance. However, the AMF inoculum pot-produced under controlled conditions was an efficient alternative for better management of A. acuminata and M. pubescens in the nursery, which in the future may be combined with defined EMF and Frankia inocula for improved management practices.

Effect of Bacillus thuringiensis (Bt) maize cultivation history on arbuscular mycorrhizal fungal colonization, spore abundance and diversity, and plant growth

Greenhouse studies have reported that maize expressing Bacillus thuringiensis (Bt) insecticidal toxins may have nontarget effects on symbiotic arbuscular mycorrhizal fungi (AMF), however, field studies have not detected the same pattern. This may be due to the short-term nature of previous field experiments, differences in soil properties between studies, or plant-soil feedbacks that influence AMF communities in roots and soil over time. In this field experiment, we used split plots to evaluate the effect of Bt or non-Bt maize cultivation history on AMF spore abundance, diversity, root colonization, and growth of seven different genotypes of Bt maize and five corresponding non-Bt parental (P) isolines. We found that Bt plants had higher leaf chlorophyll content when they were grown in plots that had been cultivated with Bt maize the previous year, and similarly, non-Bt plants had higher chlorophyll content when they were grown in plots with a non-Bt cultivation history, indicative of a positive feedback effect. There was a lower density of AMF spores in plots with a Bt maize cultivation history than in plots where P maize had been grown in the previous year, but no difference in spore diversity. Despite the differences in spore density, we found no significant differences in AMF colonization or root or shoot biomass between plots with a cultivation history of Bt and P maize. This study presents the first evidence of an effect of Bt maize cultivation on the soil ecosystem, but also provides further evidence that this effect is not necessarily large or easily detectable within the range of normal environmental variation. Management of agroecosystems will need to consider the potential effects of reduced numbers of AMF propagules in soil as this could have an effect on ecosystem processes including carbon sequestration, nutrient cycling, drought tolerance, soil aggregation, and plant resistance to pathogens. Taken together with greenhouse experiments, we can now make predictions on how Bt maize cultivation may affect AMF under different environmental conditions.

Environmental Implications of Herbicide Resistance: Soil Biology and Ecology

Soil microbial community structure and activity are linked to plant communities. Weeds may alter their soil environment, selecting for specific rhizosphere microbial communities. Rhizosphere modification occurs for many crop and horticultural plants. However, impacts of weeds in agroecosystems on soil biology and ecology have received less attention because effective weed management practices were developed to minimize their impacts on crop production. The recent development of herbicide resistance (HR) in several economically important weeds leading to widespread infestations in crop fields treated with a single herbicide has prompted a re-evaluation of the effects of weed growth on soil biology and ecology. The objective of this article is to review the potential impacts of herbicide-resistant weeds on soil biological and ecological properties based on reports for crops, weeds, and invasive plants. Persistent weed infestations likely establish extensive root systems and release various plant metabolites through root exudation. Many exudates are selective for specific soil microbial groups mediating biochemical and nutrient acquisition processes. Exudates may stimulate development of microbial groups beneficial to weed but detrimental to crop growth or beneficial to both. Changes in symbiotic and associative microbial interactions occur, especially for arbuscular mycorrhizal fungi (AMF) that are important in plant uptake of nutrients and water, and protecting from phytopathogens. Mechanisms used by weeds to disrupt symbioses in crops are not clearly described. Many herbicide-resistant weeds includingAmaranthusandChenopodiumdo not support AMF symbioses, potentially reducing AMF propagule density and establishment with crop plants. Herbicides applied to control HR weeds may compound effects of weeds on soil microorganisms. Systemic herbicides released through weed roots may select microbial groups that mediate detrimental processes such as nutrient immobilization or serve as opportunistic pathogens. Understanding complex interactions of weeds with soil microorganisms under extensive infestations is important in developing effective management of herbicide-resistant weeds.

Arbuscular mycorrhizal fungal diversity in phosphorus-deficient Alfisols of a dry North-western agro-ecosystem of Tamil Nadu, India

Semi-arid tropical soils, characterized by low soil organic carbon (SOC) with limited available macronutrients and micronutrients for crop plants, are predicated to have a yield sustainability problem in the future due to intensive cropping and limited nutrient management adoptions. Arbuscular mycorrhizal fungi (AMF), the functional link between plant and soil, play a pivotal role in nutrient cycling, organic matter stabilization and soil structure and fertility improvement. Hence, so far unexplored or underutilized, native AMF could be a potential resource for fertility management of these semi-arid tropical soils. Hence, in the present investigation, we assessed the abundance and diversity of AMF in phosphorus-deficient agricultural soils of semi-arid tropics of southern India. Our results show that the spore density and infective propagules of AMF were relatively low in these soils. The morpho-typing of extracted AMF spores revealed that these soils were dominated by glomeraceae (six species of Glomus) while species of Gigaspora, Scutellospora and Acaulospora were found in low abundance. The diversity indices assessed for the AMF species were also globally low. The non-metric multi-dimensional scaling and hierarchical cluster analysis of species richness showed variation in the community composition of AMF in the soils. The principal component analysis of the assessed soil variables suggest that the available phosphorus (P), SOC and dehydrogenase and alkaline phosphatase activities had negative impact on spore density and infective propagules of AMF with no effect on species diversity. The regression analyses reveal that the available P is the significant soil variable that drives the AMF abundance and infectivity. This study opens the possibilities of effective utilization of native mycorrhizae for agriculture in semi-arid tropical soils.

Diversity of arbuscular mycorrhizal fungi associated with Triticum aestivum L. plants growing in an Andosol with high aluminum level

Arbuscular mycorrhizal (AM) fungi contribute to agricultural productivity by improving plant nutrient and water acquisition, and modifying some physiological traits under various environmental stresses. Notwithstanding, there is a lack of knowledge about the ecology and behavior of AM fungi in acidic soils with high levels of exchangeable aluminum (Al). Therefore, we have carried out a preliminary research based on the taxonomic identification of AM fungal species associated to winter wheat habitually cropped in an Andosol from Southern Chile. Rhizosphere soils from six winter wheat cultivars (“Bakan”, “Porfiado”, “Maxi”, “Crac”, “Invento” and “Otto”) were collected from field plots. AM fungal species identification was performed based on spore morphological analyses. In this study, we additionally observed AM fungal propagules (spore density and colonization levels) at two crop stages (grain filling and postharvest). At grain filling stage, “Bakan”, “Porfiado” and “Maxi” cultivars showed higher colonization levels than “Otto”, “Crac” and “Invento” ones. Spore density increased at postharvest stage and “Maxi”, “Otto” and “Invento” cultivars presented higher spore densities than other three cultivars. Twenty-four AM fungal species were identified and subsequently classified into genera Acaulospora, Pacispora, Claroideoglomus, Glomus, Funneliformis, Septoglomus, Simiglomus, Scutellospora, Cetraspora, Ambispora, Archaeospora and Paraglomus. The Shannon–Wiener values showed no significantly difference in AM fungal diversity associated to wheat cultivars, but species richness was significant different among cultivars. Simpson's index was significantly different among AM fungal communities being Acaulospora and Scutellospora the most dominant genera. In this study, AM fungal community structure was different for specific wheat cultivar; hence the use of target AM fungal species could be determinant factor for the appropriate AM community establishment in potential inoculation assays, especially in Andosols with high aluminum levels.

The northward shifting neophyte Tragopogon dubius is just as effective in forming mycorrhizal associations as the native T. pratensis

Background: As a consequence of climate warming, many organisms are shifting their range towards higher latitudes and altitudes. As not all do so at the same speed, this may disrupt biotic interaction. Release from natural enemies through range expansion can result in invasiveness, whereas loss of mutualists can reduce plant vigour and fitness. One of the most important groups of plant symbiotic mutualists is the arbuscular mycorrhizal fungi (AMF).Aims: We used greenhouse experiments to test whether Tragopogon dubius, a species that has recently expanded its range northward and colonised the Netherlands, is able to associate with the same AMF as the native congener T. pratensis.Methods: In soils collected from four locations in the new range of T. dubius we compared the density of infective AMF propagules associating with both plant species, as well as AMF colonisation of the roots. The AMF community structure in the roots of these species was also analysed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE).Results: Tragopogon dubius and T. pratensis did not differ in any of these characteristics.Conclusions: We therefore conclude that the range-shifting T. dubius is as effective in the formation of mycorrhiza as the native congener.

HONGOS MICORRIZÓGENOS ARBUSCULARES ASOCIADOS A LA VEGETACIÓN COSTERA EN CHUBURNÁ, YUCATÁN, MÉXICO

&lt;p&gt;Plant species that successfully establish in environments of recent formation, such as barrier islands, exhibit life history traits that allow them to efficiently capture nutrients and water, such ability may be largely due to interactions these plants establish with mutualistic arbuscular mycorrhizal fungi (AMF). The goal of this work was to characterize plant community present at two sites, a barrier island and a coastal dune system; the influence of marine proximity against the lagoon proximity and to relate aspects of these plant communities to soil fertility and AMF presence in roots y la rhizosphere. The study was conducted at “La Carbonera” in Chuburná, Yucatan, Mexico. At each site we established transects, where we placed three 5 x 5-m plots. Within each plot we surveyed vegetation (recording present species and plant cover), collected root samples to assess AMF colonization, and collected soil samples for nutrient analyses and quantification of AMF spores in rhizosphere. We found a total of 36 plant species from 28 families, with herbaceous life form being the most common. All plant species recorded were colonized by AMF. Nonetheless, AMF spores were scarce in soil, which may be due to immediate AMF root colonization of host plants trigger by low phosphorus and nitrogen availability in soil. Our results suggest that the AMF propagules may colonize the roots since the first stages of plant establishment on sand dunes. &lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;