Arbuscular Mycorrhiza Colonization Research Articles

Mycorrhizal and Endophytic Fungal Colonization in Arrhenatherum elatius L. Roots According to the Soil Contamination in Heavy Metals

The aim of this work was to jointly study non-mycorrhizal (dark septate fungi) and mycorrhizal (arbuscular mycorrhizae) colonization along a large range of heavy metal pollution in soil in order to determine the effective contribution of each type of endophytes in relation to heavy metal uptake and tolerance. Hence, eight sites were chosen in the mining area of northern France with respect both to a large range of heavy metal contamination (Cd, Pb, Zn) and monospecific colonization by Arrhenatherum elatius. Root colonization with both arbuscular mycorrhizae (AM) and dark septate fungi (DSF) as well as spore density in rhizospheric soil were estimated in relation to soil characteristics. Mycorrhizal infestation (hyphae, arbuscules and vesicles) was adversely affected by soil pollution almost to exclusion. The intensity of colonization with DSF was very low in presence of AM in non-contaminated soils but higher in polluted soils. The effect of the fungal colonization on the heavy metal tolerance of Arrhenatherum elatius is discussed.

Early effects of fire on herbaceous vegetation and mycorrhizal symbiosis in high altitude grasslands of Natural Park of Estrela Mountain (PNSE)

Severe fires over the last decade have transformed the high altitude grassland biogenetic reserve in the Natural Park of Estrela Mountain (PNSE) of Portugal. Yet, there is little information about the impacts of the fires above and below ground. We assessed the species composition, richness and frequency of the herbaceous vegetation. We characterized the mycorrhizal symbiosis and analysed the soil properties in three cervunal areas of which one was destroyed by a severe fire in 2003. The results indicate that plant community in high altitude grassland of PNSE are rather poor in species but the number may increase after fire. The most remarkable change in the herbaceous vegetation after fire was the abrupt increase of Festuca trichophylla in the burnt area, to the detriment and abrupt decrease of Nardus stricta. Arbuscular mycorrhizas (AM) were the most widespread symbioses in all three grasslands. AM colonization of F. trichophylla was significantly lower in burnt grassland but the AM colonization in N. stricta increased. There was also a higher phosphorous content in soil of the burnt grassland. We put forward a hypothesis about the impacts of recurrent fires above and below ground and discuss its implications to functioning of high altitude ecosystems.

Phosphate systemically inhibits development of arbuscular mycorrhiza in Petunia hybrida and represses genes involved in mycorrhizal functioning

Most terrestrial plants form arbuscular mycorrhiza (AM), mutualistic associations with soil fungi of the order Glomeromycota. The obligate biotrophic fungi trade mineral nutrients, mainly phosphate (P(i) ), for carbohydrates from the plants. Under conditions of high exogenous phosphate supply, when the plant can meet its own P requirements without the fungus, AM are suppressed, an effect which could be interpreted as an active strategy of the plant to limit carbohydrate consumption of the fungus by inhibiting its proliferation in the roots. However, the mechanisms involved in fungal inhibition are poorly understood. Here, we employ a transcriptomic approach to get insight into potential shifts in metabolic activity and symbiotic signalling, and in the defence status of plants exposed to high P(i) levels. We show that in mycorrhizal roots of petunia, a similar set of symbiosis-related genes is expressed as in mycorrhizal roots of Medicago, Lotus and rice. P(i) acts systemically to repress symbiotic gene expression and AM colonization in the root. In established mycorrhizal roots, P(i) repressed symbiotic gene expression rapidly, whereas the inhibition of colonization followed with a lag of more than a week. Taken together, these results suggest that P(i) acts by repressing essential symbiotic genes, in particular genes encoding enzymes of carotenoid and strigolactone biosynthesis, and symbiosis-associated phosphate transporters. The role of these effects in the suppression of symbiosis under high P(i) conditions is discussed.

Fungal Root Endophyte Colonization of Fern and Lycophyte Species from the Celaque National Park in Honduras

Abstract Root endophyte colonization was investigated in 32 fern and lycophyte species of 11 families collected from the Celaque National Park in Honduras. Arbuscular mycorrhizae (AM) were found in 11 plant species (34%) of Anemiaceae, Gleicheniaceae, Ophioglossaceae, Pteridaceae, Selaginellaceae, Thelypteridaceae, and Woodsiaceae. The abundance of arbuscular mycorrhizal fungi (AMF) in roots varied with particular species, ranging from 4% (Sticherus underwoodianus) to 78% (Thelypteris patens). The morphological AM colonization pattern of all investigated species was of the Paris-type. The mycelium of dark septate endophytes (DSE) was found in 19 species (58%), and was observed both in the roots of plants that were colonized by AMF and were devoid of AM association. However, in both cases the percentage of root colonization by these fungi was low. Exceptions were Asplenium serra, Elaphoglossum erinaceum, Lellingeria prionodes, and Lycopodium thyoides, where abundant DSE hyphae were observed. Our results ar...

Mycorrhization of the notabilis and sitiens tomato mutants in relation to abscisic acid and ethylene contents

We examined whether the reduced mycorrhization of abscisic acid (ABA)-deficient tomato mutants correlates with their incapacity in ABA biosynthesis and whether this effect is dependent on ethylene production. The mycorrhization of notabilis and sitiens mutants, which have different ABA deficiencies and an excess of ethylene production, was analyzed. Comparative analysis of the ABA-deficient tomato mutants showed both quantitative and qualitative differences in the pattern of arbuscular mycorrhiza (AM) colonization between the two tomato mutant phenotypes. The sitiens mutant showed a great limitation in fungal colonization (mycorrhizal intensity and arbuscule formation) well correlated with their incapacity in ABA biosynthesis. The notabilis plants, which maintained normal ABA levels in roots under our experimental conditions, appeared to be less affected in their capacity for AM formation, and only a decrease in mycorrhizal intensity was noted at the end of the mycorrhization process. Blockage of ABA formation after tungstate application resulted in a reduction in mycorrhization of wild-type tomato plants. The transcript accumulation of the mycorrhiza-responsive LePT4 gene (tomato phosphate transporter) was clearly associated with the ABA content and mycorrhiza development in roots, as the tungstate treatment in wild-type plants and the inherent ABA deficiency in sitiens mutants led to a complete abolishment of their expression. Our results suggest that the decrease in arbuscular abundance in mycorrhizal sitiens roots is directly associated with their ABA biosynthesis deficiency, and the accumulation of ethylene, as a consequence of ABA deficiency in the mutants, primarily affects mycorrhizal intensity.

Effects of a Hurricane Disturbance on Aboveground Forest Structure, Arbuscular Mycorrhizae and Belowground Carbon in a Restored Tropical Forest

To better understand how management and restoration practices influence the response of terrestrial ecosystems to large-scale disturbances, it is critical to study above- and belowground effects. In this study, we examined the immediate effect of a major hurricane on aboveground forest structure, arbuscular mycorrhizae (AM) and belowground carbon pools in experimentally thinned plots in a tropical forest. The hurricane occurred five years after a thinning treatment, when thinned plots had similar aboveground carbon stocks but different forest structure compared to control plots. Thinned plots had more large diameter (>10 cm) trees compared to the control plots, which were characterized by a higher density of small diameter (<10 cm) trees. Despite pre-hurricane differences in forest structure, there were no significant differences between treatments in changes of canopy openness or number of affected trees following the hurricane. Thinned plots had larger belowground carbon pools than the controls plots before the hurricane, and these differences remained after the hurricane despite rapid decomposition of organic matter rich in nitrogen. There were no pre-hurricane differences in AM fungal spores or total AM root colonization. The hurricane reduced AM sporulation by nearly 50% in both treatments, yet we observed a significant increase in AM root colonization after the hurricane with greater AM colonization in the thinned plots. Hurricanes have well-known visible aboveground effects, but here we showed that less visible belowground effects are influenced by forest management and may play an important role in forest recovery.

Arbuscular Mycorrhizal Technology in Reclamation and Revegetation of Coal Mine Spoils under Various Revegetation Models

Reclamation and revegetation of a coal mine spoils with various revegetation models utilizing the mycorrhizal technology were studied. The models with different combination of plant species were designed to test the hypothesis of speedy revegetation. Root colonization and spore density of arbuscular mycorrhizae (AM) were lowest in plants seeded directly on slopes of the overburden (coal mine dump). At flat surfaces, the mycorrhizal colonization in plant species was higher than that observed at slopes. In other revegetation models, i.e., tree monoculture, tree monoculture + crop species (agroforestry), and two strata plantations (combination of different plant species), maximum AM colonization was recorded for tree species grown along with crop species. This was followed by two strata plantations and tree monoculture. In two strata plantations three categories of AM associations were recognized: 1) every plant in the combination, possessed high mycorrhizal association, 2) only one plant in the combination possessed high mycorrhizal association, and 3) none of the plants in the combination possessed high mycorrhizal association. Azadirachta indica, Pongamia pinnata, Leucaena leucocephala and Acacia catechu were most effective in catching mycorrhizae, and can be used as the effective tool in rehabilitation of the degraded ecosystems.

Arbuscular Mycorrhizal Technology in Reclamation and Revegetation of Coal Mine Spoils under Various Revegetation Models

Reclamation and revegetation of a coal mine spoils with various revegetation models utilizing the mycorrhizal technology were studied. The models with different combination of plant species were designed to test the hypothesis of speedy revegetation. Root colonization and spore density of arbuscular mycorrhizae (AM) were lowest in plants seeded directly on slopes of the overburden (coal mine dump). At flat surfaces, the mycorrhizal colonization in plant species was higher than that observed at slopes. In other revegetation models, i.e., tree monoculture, tree monoculture + crop species (agroforestry), and two strata plantations (combination of different plant species), maximum AM colonization was recorded for tree species grown along with crop species. This was followed by two strata plantations and tree monoculture. In two strata plantations three categories of AM associations were recognized: 1) every plant in the combination, possessed high mycorrhizal association, 2) only one plant in the combination possessed high mycorrhizal association, and 3) none of the plants in the combination possessed high mycorrhizal association. Azadirachta indica, Pongamia pinnata, Leucaena leucocephala and Acacia catechu were most effective in catching mycorrhizae, and can be used as the effective tool in rehabilitation of the degraded ecosystems.

Role of Bioinoculant (AM Fungi) Increasing in Growth, Flavor Content and Yield in Allium sativum L. under Field Condition

Present investigation deals with the beneficial effect of Arbuscular Mycorrhiza (AM) fungal species Glomus fasciculatum on growth performance of Allium sativum under field condition. In AM inoculated garlic plant showed significant increase in plant growth parameters like plant height, total biomass and bulb diameters, bulb weight, and yield. There was 21.10 % increment in yield of Allium bulb as compared to non AM inoculated garlic plant. Percentage of AM colonization occurred at all sampling and the colonization was higher during bulb initiation. Mycorrhiza inoculated garlic plant showed more alliin and allinase enzyme activity as compared to non inoculated garlic plant. The results reveal that mycorrhiza contribute to growth and development of garlic plant under field condition.

Arbuscular Mycorrhizal Mediated Nutrition in Plants

ABSTRACT Arbuscular mycorrhizae (AM) are the symbiotic fungi that predominate in the roots and soils of agricultural crop plants. The most recognized beneficial effect of these fungi is to enhance host plant uptake of relatively immobile nutrients, in particular phosphorus (P), and several micronutrients. The AM fungi absorb inorganic P either from the soluble P pools in the soil, or from insoluble forms such as rock phosphates as well as from insoluble organic sources. Recent studies show that mycorrhizal fungi would have access to rock phosphate through localized alterations of pH and/or by the production of organic acid anions that may act as chelating agents. The AM colonization also improves plant N nutrition. Generally mycorrhizal symbiosis more influences on nitrogen (N) uptake and translocation if ammonium (NH4 +) rather than nitrate (NO3 −) is the nitrogen source. However, under drought stress the role of mycorrhizae in NO3 − transport to the root surface may be significant as the NO3 − mobility is severely restricted due to its low concentration and diffusion rate under such circumstances. However, as yet little is known about the mechanism of N uptake by the AM fungi. Uptake of micronutrients is also influenced by mycorrhizal colonization.

Ectomycorrhizae, arbuscular mycorrhizae, and dark-septate fungi on Salix humboldtiana in two riparian populations from central Argentina

Colonization of Salix humboldtiana (Salicaceae) by ectomycorrhizae (ECM), arbuscular mycorrhizae (AM), and dark-septate endophytic (DSE) fungi was studied throughout autumn on two riparian populations in central Argentina. AM and DSE infection on roots ranged from 0% to 17% and from 2% to 20% respectively, whereas ECM colonization was higher, varying between 33% and 99% for both sites. Seven ECM morphotypes were found on S. humboldtiana roots. The nuclear rDNA internal transcriber spacer (ITS) region from the ectomycorrhizal root tips was amplified using ITS-1F and ITS-4 primers. Two of the seven ECM types were identified by searching GenBank blasts: one attributed to the genus Tomentella (Thelephoraceae) and the second most closely matched to Inocybe sp. (Cortinariaceae). The ECM colonization varied among sampling dates and sites, whereas AM and DSE colonization varied only among sampling dates. Diversity values for the ECM morphotype were not significantly different for autumn months or among the two sites. Positive correlations were found between Inocybe sp. and sites and between Inocybe sp., Tomentella sp., morphotypes III, IV, and VI, and sampling dates. This article provides the first documented evidence of co-occurrence of ECM, AM, and DSE in S. humboldtiana.

Arbuscular mycorrhizal status of some Kashmir Himalayan alien invasive plants

In view of the recently reported role of arbuscular mycorrhizas (AM) in plant invasions, we examined 63 alien plant species representing 26 families, collected from diverse habitat types in the Kashmir Himalaya, India, for the extent and type of their AM association. Based on the percent AM fungal root length colonization (% RLC), the investigated plants were categorized into five classes (class A = 0-5% RLC, class B = 6-25%, class C = 26-50%, class D = 51-75%, and class E = 76-100%). The number of species belonging to each of these classes was 7, 6, 22, 19, and 9, respectively. The AM colonization in 33 plant species was of Arum-type, 18 species was of Paris-type, and eight species harbored an intermediate type. Such baseline information on a large number of alien plants inhabiting diverse habitats in different biogeographical regions is needed for elucidating the role of AM fungi in alien plant invasions.

Ectomycorrhizae, arbuscular mycorrhizae, and dark-septate fungi on &lt;i&gt;Salix humboldtiana&lt;/i&gt; in two riparian populations from central Argentina

Colonization of Salix humboldtiana (Salicaceae) by ectomycorrhizae (ECM), arbuscular mycorrhizae (AM), and dark-septate endophytic (DSE) fungi was studied throughout autumn on two riparian populations in central Argentina. AM and DSE infection on roots ranged from 0% to 17% and from 2% to 20% respectively, whereas ECM colonization was higher, varying between 33% and 99% for both sites. Seven ECM morphotypes were found on S. humboldtiana roots. The nuclear rDNA internal transcriber spacer (ITS) region from the ectomycorrhizal root tips was amplified using ITS-1F and ITS-4 primers. Two of the seven ECM types were identified by searching GenBank blasts: one attributed to the genus Tomentella (Thelephoraceae) and the second most closely matched to Inocybe sp. (Cortinariaceae). The ECM colonization varied among sampling dates and sites, whereas AM and DSE colonization varied only among sampling dates. Diversity values for the ECM morphotype were not significantly different for autumn months or among the two sites. Positive correlations were found between Inocybe sp. and sites and between Inocybe sp., Tomentella sp., morphotypes III, IV, and VI, and sampling dates. This article provides the first documented evidence of co-occurrence of ECM, AM, and DSE in S. humboldtiana.

Root-Fungal Associations of Colobanthus Quitensis and Deschampsia Antarctica in the Maritime and Subantarctic

ABSTRACTThe two native Antarctic vascular plant species, Colobanthus quitensis and Deschampsia antarctica, were sampled from 15 points along a 1480 km latitudinal transect from South Georgia (54°S, 36°W) through to the Léonie Islands on the western Antarctic Peninsula (67°S, 68°W). Roots of plants were cleared and stained and fungal structures recorded. The commonest type of fungal association was that formed by dark septate endophytes (DSE): 32% and 27% of the root lengths of C. quitensis and D. antarctica were colonized by hyphae of these fungi, respectively. Hyaline and stained septate hyphae were also common in roots. Coarse and fine arbuscular mycorrhiza (AM) occurred in the roots of both plant species from South Georgia, and fine AM colonization with occasional arbuscules was also sporadically recorded in roots from the South Shetland Islands, suggesting functional associations between higher plants and AM symbionts. Fungal abundances were not associated with soil chemistry, but AM abundance was associated with seasonal surface air temperature, with lower colonization in more southerly, colder habitats. We conclude that DSE are widespread, and that AM fungi are sparse but present and decline in abundance at higher latitudes, in the roots of C. quitensis and D. antarctica.

Arbuscular Mycorrhizas and Dark Septate Fungi in Lycopodium paniculatum (Lycopodiaceae) and Equisetum bogotense (Equisetaceae) in a Valdivian Temperate Forest of Patagonia, Argentina

ABSTRACT Arbuscular mycorrhizas (AM) are one of the most widespread and common type of symbiotic associations. Lycopodium paniculatum and Equisetum bogotense are two important species of seedless vascular plants in a Valdivian temperate forest of Patagonia, Argentina. The mycorrhizal status of these species is completely unknown, as it is for most lycophytes and monilophytes in Argentina, where information on symbiotic interactions in these plants is scarce. In this study, typical AM structures were observed in sporophytes of L. paniculatum and E. bogotense. The percentage of root length colonized by AM fungi ranged from 0 to 50% in the first species and from 0 to 22.5% in E. bogotense. Both species were facultative mycorrhizal and it was observed that the habitat and substrate seem to play an important role in determining the colonization intensity. The morphological AM colonization pattern was considered an Intermediate-type. Dark septate fungi, characterized by septate hyphae and microsclerotia, were a...

Prepenetration apparatus assembly precedes and predicts the colonization patterns of arbuscular mycorrhizal fungi within the root cortex of both Medicago truncatula and Daucus carota.

Arbuscular mycorrhizas (AM) are widespread, ancient endosymbiotic associations that contribute significantly to soil nutrient uptake in plants. We have previously shown that initial fungal penetration of the host root is mediated via a specialized cytoplasmic assembly called the prepenetration apparatus (PPA), which directs AM hyphae through the epidermis (Genre et al., 2005). In vivo confocal microscopy studies performed on Medicago truncatula and Daucus carota, host plants with different patterns of AM colonization, now reveal that subsequent intracellular growth across the root outer cortex is also PPA dependent. On the other hand, inner root cortical colonization leading to arbuscule development involves more varied and complex PPA-related mechanisms. In particular, a striking alignment of polarized PPAs can be observed in adjacent inner cortical cells of D. carota, correlating with the intracellular root colonization strategy of this plant. Ultrastructural analysis of these PPA-containing cells reveals intense membrane trafficking coupled with nuclear enlargement and remodeling, typical features of arbusculated cells. Taken together, these findings imply that prepenetration responses are both conserved and modulated throughout the AM symbiosis as a function of the different stages of fungal accommodation and the host-specific pattern of root colonization. We propose a model for intracellular AM fungal accommodation integrating peri-arbuscular interface formation and the regulation of functional arbuscule development.

Arbuscular Mycorrhizal Colonization Response to Three Seed‐Applied Fungicides

In soybean [Glycine max (L.) Merr.], arbuscular mycorrhizae (AM) enhance nutrient and water status and may increase root resistance to soilborne pathogens. However, the fungicides that are routinely applied to the seed may reduce AM colonization, reducing these benefits. Thus, the objective of this research was to assess the effect of three commonly used seed‐applied fungicides on AM colonization of soybean in Iowa. Soybean seeds were treated with the fungicides mefenoxam, fludioxonil, mefenoxam + fludioxonil, and a nontreated control. Soil fumigation with a mixture of 1,3‐dichloropropene and chloropicrin was used as a tool to measure any direct effect of the fungicide on plant growth or yield parameters. There was a significant fumigation by seed treatment interaction in 2005. Seed‐applied fungicides that contained fludioxonil favored AM colonization in nonfumigated soil, where fludioxonil‐treated plants had double the root colonization of the control (6 vs. 2.8%, respectively) and five times more root colonization than plants treated with mefenoxam (6 vs. 1.1%, respectively). In the fumigated soil, plants treated with mefenoxam alone or in combination with fludioxonil had lower colonization than the control and fludioxonil‐treated plants. Fumigation did not significantly reduce or increase mycorrhizal colonization across locations. No differences in grain yield, final stand, or grain composition were found among seed‐applied fungicides or between nonfumigated and fumigated soil. With the exception of mefenoxam in fumigated soil in 2005, there was no evidence of a reduction in mycorrhizal colonization of soybean roots with seed‐applied fungicides under field conditions.

Seasonal and temporal dynamics of arbuscular mycorrhizal and dark septate endophytic fungi in a tallgrass prairie ecosystem are minimally affected by nitrogen enrichment

Root colonization by arbuscular mycorrhizae (AM) and dark septate endophytic (DSE) fungi in nitrogen amended and unamended mixed tallgrass prairie communities were analyzed monthly over two growing seasons. Roots were stained with Trypan blue and Sudan IV and fungal structures quantified using the modified magnified intersections method. Root length colonized (RLC) by DSE exceeded AM colonization during early part of the growing season. Fungal colonization varied among the years and was greater in 2003 than in 2002. Seasonal variation among the months within a growing season was observed in 2002 but not in 2003 for both AM and DSE. AM fungi were most abundant during the peak growing season of dominant C4 vegetation while DSE were most abundant during the early part of the growing season. Hyperparasitism of AM hyphal coils by melanized septate fungi was frequently observed and increased with AM coil frequency. Although nitrogen amendment had altered the plant community composition, it had no impact on the colonization by AM or DSE fungi.

Relationships among Three Pathways for Resource Acquisition and their Contribution to Plant Performance in the Emergent Aquatic Plant Lythrum salicaria (L.)

Three pathways for resource acquisition exist in the emergent aquatic plant, Lythrum salicaria (L.); a subterranean root system, a free-floating adventitious root system, and arbuscular mycorrhiza (AM) fungal hyphae colonizing subterranean roots. This study examined the relationship(s) among these pathways and their contribution to plant performance. If the free-floating adventitious root system and/or AM fungi contribute to plant growth in wetland habitats, we predicted that their absence would result in a significant reduction in plant performance. Furthermore, if a reduction in resource uptake, effected by an absence of free-floating adventitious roots and/or AM fungi, is compensated for by increased allocation to remaining pathway(s) for resource uptake, we predicted altered patterns of resource allocation among shoots and the remaining pathway(s) for resource uptake. Contrary to our predications, plants experiencing adventitious root removal and/or grown in the absence of AM fungi generally had greater biomass and total shoot height than controls. Similarly, while levels of AM colonization and subterranean root biomass displayed a treatment effect, the observed responses did not correspond with our predictions. This was also true for shoot : subterranean root dry weight ratios. Our results indicate that there is interaction among the 3 pathways for resource acquisition in L. salicaria and an effect on plant performance. The adaptive significance of these characteristics is unclear, highlighting the potential difficulties in extrapolating from terrestrial to aquatic plant species and among aquatic plant species with potentially different life history strategies.

Seasonal patterns of cadmium accumulation in Arrhenatherum elatius ( Poaceae): Influence of mycorrhizal and endophytic fungal colonisation

We investigated the influence of arbuscular mycorrhizae (AM) and dark septate fungi (DSF) colonisation on cadmium (Cd) accumulation in Arrhenatherum elatius from heavy metal-contaminated sites. AM colonisation disappeared when Cd concentrations in soil increased, while DSF infection was weak but constant throughout the experiment indicating that soil heavy metals are toxic to AM but not to DSF. AM colonisation was greatest when plant Cd concentrations were highest providing evidence that AM colonisation may influence Cd accumulation. In addition, the disappearance of AM and the concomitant reduction of Cd in shoots during seed maturation result in our suggestion that seasonal variation in AM may play a role in protecting developing seeds from soil pollution.