Hyphae Of Arbuscular Mycorrhizal Fungi Research Articles

A key role for arbuscular mycorrhiza in plant acquisition of P from sewage sludge recycled to soil

Dried and incinerated sewage sludge (SS) have the potential to be used as phosphorus (P) fertilisers. Arbuscular mycorrhizal fungi (AMF) contribute to plant P uptake; however, their role in P uptake from SS has yet to be fully explored. A compartmented pot system with an isotope pool dilution approach was used to investigate wheat (Triticum aestivum L.) P uptake from soluble P, dried SS and incinerated SS, via roots and/or AMF hyphae. Wheat was sown into an inner compartment containing a 33P label with/without AMF (Rhizophagus irregularis) inoculum. An outer soil compartment contained the P source. Compartments were separated by mesh of different sizes to allow root and/or AMF hyphal access. Plants obtained P from dried SS via AMF but there was limited evidence that plants obtained P from incinerated SS via AMF. Phosphorus uptake was significantly greater when both roots and hyphae could access dried SS than when only roots could access dried SS. We discuss the results in terms of availability of P to roots and hyphae. We conclude that AMF play an important role in wheat P acquisition from dried SS and therefore can assist in the recycling of P in waste.

Topsoil Stockpiling in Restoration: Impact of Storage Time on Plant Growth and Symbiotic Soil Biota

Addressing plant-soil relationships within restoration science may improve success and reduce costs. Here we assess the question of topsoil storage time: how does stockpile age impact plant biomass and soil microbial activity, particularly root symbionts such as rhizobia and arbuscular mycorrhizal fungi (AMF)? Working in Western Australia and in sandy soils, we grew a legume species <i>Acacia saligna</i> (Fabaceae) in one-, two-, three-, five- and ten-year-old stockpile soils under controlled glasshouse conditions. We assessed whether plant biomass, specific root length, and root diameter decreased with stockpile age. Further, we investigated how stockpile age affected the distribution and the number of effective nodules, nodule biomass and AMF colonization in roots. These above and belowground traits were chosen because they reflect the <i>A. saligna</i> response to growing in soils stockpiled for 1–10 years. We hypothesised that in older stockpiles there would be fewer rhizobial and AMF propagules which would constrain <i>A. saligna</i> growth, whereas in younger stockpiles there would be more rhizobial and AMF propagules, and <i>A. saligna</i> growth would be facilitated via these root symbionts. Using generalized linear mixed models, we found that total plant biomass was the lowest but AMF percent colonization was the highest when <i>A. saligna</i> was grown in ten-year-old soils, suggesting that AMF spores and hyphae are present in old stockpiles. Our results demonstrate that AMF communities may be initially disrupted by soil disturbance and storage, and then begin to re-establish between 5–10 years after stockpiling. However, other soil microbial communities, such as fungal pathogens that were not assessed in this study may have been responsible for decreased <i>A. saligna</i> biomass in older soils. Further research, particularly on other soil microbial communities, is needed to understand restoration success using stockpiled soil older than ten years.

Root morphology and mycorrhizal type strongly influence root production in nutrient hot spots of mixed forests

Abstract Plants compete for nutrients using a range of strategies. We investigated nutrient foraging within nutrient hot‐spots simultaneously available to plant species with diverse root traits. We hypothesized that there would be more root proliferation by thin‐root species than by thick‐root species, and that root proliferation by thin‐root species would limit root proliferation by thick‐root species. We conducted a root ingrowth experiment in a temperate forest in eastern USA where root systems of different tree species could interact. Tree species varied in the thickness of their absorptive roots, and were associated with either ectomycorrhizal (EM) or arbuscular mycorrhizal (AM) fungi. Thus, there were thin‐ and thick‐root AM and thin‐ and thick‐root EM plant functional groups. Half the ingrowth cores were amended with organic nutrients (dried green leaves). Relative root length abundance, the proportion of total root length in a given soil volume occupied by a particular plant functional group, was calculated for the original root population and ingrowth roots after 6 months. The shift in relative root length abundance from original to ingrowth roots was positive in thin‐root species but negative in thick‐root species (p &lt; .001), especially in unamended patches (AM: +6% vs. −7%; EM: +8% vs. −9%). Being thin‐rooted may thus allow a species to more rapidly recolonize soil after a disturbance, which may influence competition for nutrients. Moreover, we observed that nutrient additions amplified the shift in root length abundance of thin over thick roots in AM trees (+13% vs. −14%), but not in EM trees (+1% vs −3%). In contrast, phospholipid fatty acid biomarkers suggested that EM fungal hyphae strongly proliferated in nutrient hot‐spots whereas AM fungal hyphae exhibited only modest proliferation. We found no evidence that when growing in the shared patch, the proliferation of thin roots inhibited the growth of thick roots. Synthesis. Knowledge of root morphology and mycorrhizal type of co‐existing tree species may improve prediction of patch exploitation and nutrient acquisition in heterogeneous soils.

Comparison of arbuscular mycorrhizal fungal effects on the heavy metal uptake of a host and a non-host plant species in contact with extraradical mycelial network

The effects of inoculation with an arbuscular mycorrhizal (AM) fungus on Cd and Ni tolerance and uptake in Medicago sativa, an AM host, and Sesuvium portulacastrum, a non-host plant, were investigated in a greenhouse experiment. The plants were cultivated in sterilized sand in a two-compartmented system, which prevented root competition but enabled colonization of the whole substrate by AM fungal extraradical mycelium. M. sativa was either left non-inoculated or inoculated with the AM fungus Rhizophagus irregularis, and both plants were either cultivated without heavy metal (HM) addition or supplied with cadmium (Cd) or nickel (Ni), each in two doses. Additional pots with singly cultivated plants were established to control for the effect of the co-cultivation. AM significantly enhanced the growth of M. sativa and substantially increased its uptake of both HMs. The roots of S. portulacastrum became colonized by AM fungal hyphae and vesicles. The presence of the AM fungus in the cultivation system tended to increase the HM uptake of S. portulacastrum, but the effect was less consistent and pronounced than that in M. sativa. We conclude that AM fungal mycelium radiating from M. sativa did not negatively affect the growth and HM uptake of S. portulacastrum. On the contrary, we hypothesize that it stimulated the absorption and translocation of Cd and Ni in the non-host species. Thus, our results suggest that AM fungal mycelium radiating from mycorrhizal plants does not decrease the HM uptake of non-host plants, many of which are considered promising candidate plants for phytoremediation.

Aboveground Epichloë coenophiala-Grass Associations Do Not Affect Belowground Fungal Symbionts or Associated Plant, Soil Parameters.

Cool season grasses host multiple fungal symbionts, such as aboveground Epichloë endophytes and belowground arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSEs). Asexual Epichloë endophytes can influence root colonization by AMF, but the type of interaction-whether antagonistic or beneficial-varies. In Schedonorus arundinaceus (tall fescue), Epichloë coenophiala can negatively affect AMF, which may impact soil properties and ecosystem function. Within field plots of S. arundinaceus that were either E. coenophiala-free (E-), infected with the common, mammal-toxic E. coenophiala strain (CTE+), or infected with one of two novel, non-toxic strains (AR542 NTE+ and AR584 NTE+), we hypothesized that (1) CTE+ would decrease AMF and DSE colonization rates and reduce soil extraradical AMF hyphae compared to E- or NTE+, and (2) this would lead to E- and NTE+ plots having greater water stable soil aggregates and C than CTE+. E. coenophiala presence and strain did not significantly alter AMF or DSE colonization, nor did it affect extraradical AMF hypha length, soil aggregates, or aggregate-associated C and N. Soil extraradical AMF hypha length negatively correlated with root AMF colonization. Our results contrast with previous demonstrations that E. coenophiala symbiosis inhibits belowground AMF communities. In our mesic, relatively nutrient-rich grassland, E. coenophiala symbiosis did not antagonize belowground symbionts, regardless of strain. Manipulating E. coenophiala strains within S. arundinaceus may not significantly alter AMF communities and nutrient cycling, yet we must further explore these relationships under different soils and environmental conditions given that symbiont interactions can be important in determining ecosystem response to global change.

Arbuscular Mycorrhizal Fungal Hyphae Alter Soil Bacterial Community and Enhance Polychlorinated Biphenyls Dissipation

We investigated the role of arbuscular mycorrhizal fungal (AMF) hyphae in alternation of soil microbial community and Aroclor 1242 dissipation. A two-compartment rhizobox system with double nylon meshes in the central was employed to exclude the influence of Cucurbita pepo L. root exudates on hyphal compartment soil. To assess the quantitative effect of AMF hyphae on soil microbial community, we separated the hyphal compartment soil into four horizontal layers from the central mesh to outer wall (e.g., L1–L4). Soil total PCBs dissipation rates ranged from 35.67% of L4 layer to 57.39% of L1 layer in AMF inoculated treatment, which were significant higher than the 17.31% of the control (P < 0.05). The dissipation rates of tri-, tetrachlorinated biphenyls as well as the total PCBs were significantly correlated with soil hyphal length (P < 0.01). Real-time quantitative PCR results indicated that the Rhodococcus-like bphC gene was 2–3 orders of magnitude more than that of Pseudomonas-like bphC gene, and was found responded positively to AMF. Phylogenetic analyses of the 16S rDNA sequenced by the Illumina Miseq sequencing platform indicated that AMF hyphae altered bacterial community compositions. The phylum Betaproteobacteria and Actinobacteria were dominated in the soil, while Burkholderiales and Actinomycetales were dominated at the order level. Taxa from the Comamonadaceae responded positively to AMF and trichlorinated biphenyl dissipation, while taxa from the Oxalobacteraceae and Streptomycetaceae responded negatively to AMF and PCB congener dissipation. Our results suggested that the AMF hyphal exudates as well as the hyphae per se did have quantitative effects on shaping soil microbial community, and could modify the PCBs dissipation processes consequently.

Bacteria with Phosphate Solubilizing Capacity Alter Mycorrhizal Fungal Growth Both Inside and Outside the Root and in the Presence of Native Microbial Communities.

Arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing Pseudomonas bacteria (PSB) could potentially interact synergistically because PSB solubilize phosphate into a form that AMF can absorb and transport to the plant. However, very little is known about the interactions between these two groups of microorganisms and how they influence the growth of each other. We tested whether different strains of bacteria, that have the capacity to solubilize phosphate, are able to grow along AMF hyphae and differentially influence the growth of AMF both outside the roots of carrot in in vitro conditions and inside the roots of potato in the presence of a microbial community. We found strong effects of AMF on the growth of the different bacterial strains. Different bacterial strains also had very strong effects on the growth of AMF extraradical hyphae outside the roots of carrot and on colonization of potato roots by AMF. The differential effects on colonization occurred in the presence of a microbial community. Our results show that these two important groups of rhizosphere microorganisms indeed interact with each other. Such interactions could potentially lead to synergistic effects between the two groups but this could depend on whether the bacteria truly solubilize phosphate in the rhizosphere in the presence of microbial communities.

Organic Nitrogen-Driven Stimulation of Arbuscular Mycorrhizal Fungal Hyphae Correlates with Abundance of Ammonia Oxidizers.

Large fraction of mineral nutrients in natural soil environments is recycled from complex and heterogeneously distributed organic sources. These sources are explored by both roots and associated mycorrhizal fungi. However, the mechanisms behind the responses of arbuscular mycorrhizal (AM) hyphal networks to soil organic patches of different qualities remain little understood. Therefore, we conducted a multiple-choice experiment examining hyphal responses to different soil patches within the root-free zone by two AM fungal species (Rhizophagus irregularis and Claroideoglomus claroideum) associated with Medicago truncatula, a legume forming nitrogen-fixing root nodules. Hyphal colonization of the patches was assessed microscopically and by quantitative real-time PCR (qPCR) using AM taxon-specific markers, and the prokaryotic and fungal communities in the patches (pooled per organic amendment treatment) were profiled by 454-amplicon sequencing. Specific qPCR markers were then designed and used to quantify the abundance of prokaryotic taxa showing the strongest correlation with the pattern of AM hyphal proliferation in the organic patches as per the 454-sequencing. The hyphal density of both AM fungi increased due to nitrogen (N)-containing organic amendments (i.e., chitin, DNA, albumin, and clover biomass), while no responses as compared to the non-amended soil patch were recorded for cellulose, phytate, or inorganic phosphate amendments. Abundances of several prokaryotes, including Nitrosospira sp. (an ammonium oxidizer) and an unknown prokaryote with affiliation to Acanthamoeba endosymbiont, which were frequently recorded in the 454-sequencing profiles, correlated positively with the hyphal responses of R. irregularis to the soil amendments. Strong correlation between abundance of these two prokaryotes and the hyphal responses to organic soil amendments by both AM fungi was then confirmed by qPCR analyses using all individual replicate patch samples. Further research is warranted to ascertain the causality of these correlations and particularly which direct roles (if any) do these prokaryotes play in the observed AM hyphal responses to organic N amendment, organic N utilization by the AM fungus and its (N-unlimited) host plant. Further, possible trophic dependencies between the different players in the AM hyphosphere needs to be elucidated upon decomposing the organic N sources.

Interactions between biochar and mycorrhizal fungi in a water-stressed agricultural soil.

Biochar may alleviate plant water stress in association with arbuscular mycorrhizal (AM) fungi but research has not been conclusive. Therefore, a glasshouse experiment was conducted to understand how interactions between AM fungi and plants respond to biochar application under water-stressed conditions. A twin chamber pot system was used to determine whether a woody biochar increased root colonisation by a natural AM fungal population in a pasture soil ('field' chamber) and whether this was associated with increased growth of extraradical AM fungal hyphae detected by plants growing in an adjacent ('bait') chamber containing irradiated soil. The two chambers were separated by a mesh that excluded roots. Subterranean clover was grown with and without water stress and harvested after 35, 49 and 63days from each chamber. When biochar was applied to the field chamber under water-stressed conditions, shoot mass increased in parallel with mycorrhizal colonisation, extraradical hyphal length and shoot phosphorus concentration. AM fungal colonisation of roots in the bait chamber indicated an increase in extraradical mycorrhizal hyphae in the field chamber. Biochar had little effect on AM fungi or plant growth under well-watered conditions. The biochar-induced increase in mycorrhizal colonisation was associated with increased growth of extraradical AM fungal hyphae in the pasture soil under water-stressed conditions.

Resolving the 'nitrogen paradox' of arbuscular mycorrhizas: fertilization with organic matter brings considerable benefits for plant nutrition and growth.

Arbuscular mycorrhizal fungi (AMF) can transfer nitrogen (N) to host plants, but the ecological relevance is debated, as total plant N and biomass do not generally increase. The extent to which the symbiosis is mutually beneficial is thought to rely on the stoichiometry of N, phosphorus (P) and carbon (C) availability. While inorganic N fertilization has been shown to elicit strong mutualism, characterized by improved plant and fungal growth and mineral nutrition, similar responses following organic N addition are lacking. Using a compartmented microcosm experiment, we determined the significance to a mycorrhizal plant of placing a 15N‐labelled, nitrogen‐rich patch of organic matter in a compartment to which only AMF hyphae had access. Control microcosms denied AMF hyphal access to the patch compartment. When permitted access to the patch compartment, the fungus proliferated extensively in the patch and transferred substantial quantities of N to the plant. Moreover, our data demonstrate that allowing hyphal access to an organic matter patch enhanced total plant N and P contents, with a simultaneous and substantial increase in plant biomass. Furthermore, we demonstrate that organic matter fertilization of arbuscular mycorrhizal plants can foster a mutually beneficial symbiosis based on nitrogen transfer, a phenomenon previously thought irrelevant.

Long-term agricultural management maximizing hay production can significantly reduce belowground C storage

Liming and fertilization of grasslands have been used for centuries to sustain hay production. Besides improving hay yields, these practices induce compositional shifts in plant and soil microbial communities, including symbiotic arbuscular mycorrhizal (AM) fungi. However, in spite of increasing interest in soil carbon (C) sequestration to offset anthropogenic CO2 emissions, little is known about the long-term effects of these agronomic interventions on soil C stocks. We examined how plants, AM fungi, and soil C respond to more than seven decades of annual applications of lime, mineral nitrogen (N), and mineral phosphorus (P) to test the hypotheses that (1) management practices increasing aboveground plant production decrease C allocation to roots, AM fungi and the soil; and (2) the relative availability of N and P predicts belowground C allocation in a consistent manner. Our study was conducted at the Rengen Grassland Experiment, established in 1941. Lime combined with N increased hay yields and promoted development of AM fungal hyphae in soil, while reducing relative C allocation to roots. Simultaneous enrichment of soil with lime, N, and P further boosted hay production, promoted grasses and suppressed other plant functional groups. This treatment also decreased soil organic C and strongly suppressed AM fungi in the soil, although the response to P varied among different AM fungal taxa. Our results indicate that agricultural management practices aimed at maximization of hay production may, in the long run, significantly (−20%) reduce belowground C storage. This is a great concern with respect to the intended use of grasslands as anthropogenic CO2 sinks because the fertilization-induced decrease in soil C stocks can partly or fully negate the C sequestration potential of the grassland ecosystems as a whole.

Impact of Funneliformis mosseae on the growth, lead uptake, and localization of Sophora viciifolia.

On the basis of a pot experiment under lead (Pb) stress, we investigated the effects of an arbuscular mycorrhizal (AM) fungus (Funneliformis mosseae) on the growth and Pb uptake of Sophora viciifolia L., and explored the Pb localization in AM roots using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that high Pb levels (500 and 1000 μg/g) inhibited the growth of S. viciifolia seedlings. Compared with the noninoculation treatment, F. mosseae inoculation decreased the Pb concentrations above- and belowground by 61.0% and 15.2%, when exposed to Pb at a concentration of 1000 μg/g. The root length, fork number, tip number, surface area, and volume of mycorrhizal S. viciifolia were higher than those of the corresponding nonmycorrhizal plants. These parameters of mycorrhizal plants increased by 220%, 219%, 157%, 225%, and 278% when plants were exposed to Pb at 1000 μg/g compared with nonmycorrhizal plants. The ratio of root length with diameters between 0-0.2 mm to the total root length significantly increased under Pb stress, and F. mosseae inoculation significantly reduced the ratio. Under Pb stress, F. mosseae increased the ratios of root length with 0.61-0.8 and 0.81-1.0 mm diameters to the total root length, indicating that F. mosseae tended to thicken the roots of S. viciifolia under Pb additions. The combined results of TEM and EDS indicated that Pb deposited in not only plant cells but also the cell walls and vacuoles of the AM fungal intracellular hyphae, thus revealing the subcellular-level mechanism of AM fungi in alleviating the Pb toxicity to the host plant.

Can biochar increase the bioavailability of phosphorus?

A large proportion of phosphate (P) fertilizer applied to Andosols reacts with reactive aluminum (Al) and iron (Fe) to become unavailable for plant uptake. We investigated whether biochar could enhance plant growth by (i) mobilizing soil P through changing soil pH or facilitating the growth of arbuscular mycorrhizal fungi (AMF), and/or (ii) introducing additional P. We grew Lotus pedunculatus cv barsille in two Andosols of contrasting P status amended with three biochars (with distinct porosity, nutrient and liming properties) at a dose of 10 t ha-1 for 32 weeks. The growth medium was divided into a root and a hyphal zone through a nylon mesh and a tephra layer that allowed the P in the hyphal zone to be transferred only by AMF hyphae. The addition of a relative nutrient-rich biochar (e.g. made from willow woodchips) with liming properties to the root zone of the P-deficient soil increased plant growth by 59% and P uptake by 73%. Pine-based biochar provided no extra nutrient acquisition and no plant-growth stimulation when added to the root zone of the P-deficient soil. However,when hyphae of those plants had access to a P-rich soil patch, the presence of pine biochar in the soil patch greatly enhanced P uptake and plant growth (e.g., by 76% and 40% when using biochar produced at 450oC compared to the absence of it). None of the tested biochars conferred advantages in the root zone of a high-P soil. We concluded that the benefits from biochar addition to nutrient uptake and plant growth are biochar- and soil-specific. Thus, biochars need to be tailored-made for certain soils by optimizing feedstock and pyrolysis conditions before application.

Arbuscular mycorrhizal fungal hyphae reduce soil erosion by surface water flow in a greenhouse experiment

The role of arbuscular mycorrhizal fungi (AMF) in resisting surface flow soil erosion has never been tested experimentally. We set up a full factorial greenhouse experiment using Achillea millefolium with treatments consisting of addition of AMF inoculum and non-microbial filtrate, non-AMF inoculum and microbial filtrate, AMF inoculum and microbial filtrate, and non-AMF inoculum and non-microbial filtrate (control) which were subjected to a constant shear stress in the form of surface water flow to quantify the soil detachment rate through time. We found that soil loss can be explained by the combined effect of roots and AMF extraradical hyphae and we could disentangle the unique effect of AMF hyphal length, which significantly reduced soil loss, highlighting their potential importance in riparian systems.

Potential Selection of Arbuscular Mycorrhizal Fungi (AMF) Indigenous Ultisols through the Production of Glomalin

The arbuscular mycorrhizal fungi ( AMF ) with plants able to increase the capacity of plants to absorb nutrients and water from the soil. Recently, research was indicated that AMF hyphae containing glomalin as a glycoprotein that serves to unify the dispersed soil particles. The content of glomalin in soil is positively correlated with soil aggregate stability. The research potential of AMF species indigenous of Ultisol Darmasraya District of West Sumatra and glomalin production in experimental pots of sterile sand medium has been carried out. The purpose of this study was to determine the diversity of AMF species on Ultisol and to seeking indigenous AMF isolates that had the best glomalin production capability. AMF spores were isolated and identified from the rhizosphere soil of corn in Ultisol. AMF species that had been identified experimentally were tested in culture medium pot of sand and zeolite (w / w 1:1) using corn crops. The results found nine of the AMF species indigenous of Ultisol Darmasraya, namely Acaulospora scrobiculata, Glomus etunicatum, Glomus luteum, Glomus mosseae, Glomus verruculosum, Glomus versiforme, Scutellospora gregaria, Scutellospora heterogama and Gigaspora sp. AMF species that showed better colonization ability in corn was G. luteum, G. verruculosum and G. versiforme. All three species produced glomalin significantly higher than the other species, i.e. 1.29 mg g-1; 1.17 mg g-1; 1.15 mg g-1, respectively. [How to Cite: Eddiwal, A Saidi, I Lenin, EF Husin and A Rasyidin. 2014. Potential Selection of Arbuscular Mycorrhizal Fungi (AMF) Indigenous Ultisols through the Production of Glomalin. J Trop Soils 19: 181-189. Doi: 10.5400/jts.2014.19.3.181]

ARBUSCULAR MYCORRHIZAL SYMBIOSIS, ECOSYSTEM PROCESSES AND ENVIRONMENTAL CHANGES IN TROPICAL SOILS

Arbuscular mycorrhizal fungi (AMF) are more widely distributed and associate with a wide range of plant species. AMF are keystone organisms that form an interface between soils and plant roots, and are sensitive to changes in soil and plant conditions. They are important microbial symbioses for plants and under conditions of P-limitation and are significant in the maintenance of soil health and fertility. AMF are crucial for the functioning of terrestrial ecosystems and plants form symbiotic interactions with AMF and colonize more than 80% of plant roots. Mycorrhizal fungi are known to influence plant diversity patterns in a variety of ecosystems globally. AMF hyphae form an extensive network in soil and length is a common parameter used to quantifying fungal hyphae. The mycelial network of AM fungi extends into the soil volume and greatly increases the surface area for uptake of immobile nutrients. Also, AM symbioses improve drought tolerance of plants and enhance tolerance of or resistance to root pathogens. Furthermore, networks of AM hyphae play a role in the formation of stable soil aggregates, building up a macroporous structure of soil that allows penetration of water and air and prevents erosion. The functioning of AMF symbiosis is mediated by direct and indirect effects of biotic and abiotic factors of the surrounding rhizosphere, community, and ecosystem. They have great potential in the restoration of disturbed land and low fertility soil. Little is known about the effects of environmental changes on AMF abundance, activity and the impact on ecosystem services. Also, we still have much to learn regarding the extent of mycorrhizal fungal diversity. It is critical to gain a clearer understanding of functional variation among AM fungal species to guide conservation and restoration efforts.

How important is the mycorrhizal pathway for plant Zn uptake?

Formation of arbuscular mycorrhizas can enhance plant uptake of immobile nutrients such as zinc (Zn) and phosphorus (P). Enhancement of Zn uptake by arbuscular mycorrhizal (AM) fungi on Zn-deficient soils has been studied previously, however, the quantity of Zn that is contributed by the AM pathway of uptake to the plant has not previously been reported for soil of any Zn status. We grew a mycorrhiza-defective mutant tomato (Solanum lycopersicum L.) genotype (rmc) and its mycorrhizal wild-type progenitor (76R) in pots containing a hyphal compartment (HC) accessible only by the external hyphae of AM fungi, and containing the radioisotope 65Zn. This was repeated at three soil Zn concentrations, ranging from low to high. We estimated the amount of Zn delivered via both the AM and direct (root) pathways. Up to 24 % of Zn in the shoots of the AM plants was delivered via the AM pathway at the lowest soil Zn treatment. This decreased significantly, to 8 %, as soil Zn concentration increased. No 65Zn was detected in the tissues of the non-mycorrhizal genotype. The relative contribution to shoot Zn by the AM pathway of uptake was highest when soil Zn was low, and decreased with increasing soil Zn concentration.

Long-term fertilizer application effects on the soil, root arbuscular mycorrhizal fungi and community composition in rotation agriculture

Arbuscular mycorrhizal fungi (AMF) play key roles in plant growth, ecosystem sustainability and stability. However, it is still unclear how the soil, root AMF growth and community composition are affected by fertilizer application in subtropical wheat–rice rotation agro-ecosystems. We investigated the impact of different organic and/or inorganic fertilizers on AMF growth and community composition in a long-term experiment field in Zhejiang Province, east China. AMF biomass was determined using 16:1ω5 phospholipid fatty acids (PLFAs) and neutral lipid fatty acids (NLFAs) content. Soil and root AMF community compositions were determined by DGGE analysis, cloning, sequencing and phylogenetic analyses. The root colonization rate was not significantly affected by different fertilizer regimes. Manure amendment significantly enhanced both AMF hyphal (i.e., 16:1ω5 PLFA) and spore (i.e., 16:1ω5 NLFA) biomass content, while inorganic fertilizer only increased the AMF spore biomass. A total of 10 and 11 Glomeromycota phylotypes were detected in soil and root samples, respectively. Glomus was the dominant genus in both soil and root samples, while Acaulospora genus occurred in roots only. Although the different fertilizers altered soil AMF communities, the root AMF community structure was not significantly altered. Soil pH (F=5.695, P<0.01) and available K (F=4.888, P<0.01) contributed to both soil and root AMF community composition, while the C/P ratio (F=3.893, P<0.01) only contributed to soil AMF community. The data suggests that high soil organic C content benefits AMF growth, while soil pH and available K concentration strongly influence AMF community. The root AMF community was much more resilient to the changes caused by long-term fertilizer application than the soil community.

In Vitro Cu-Sequestration by Glomalin from Acaulospora spinosa Walker and Trappe

The present study reveals the development of the relationship between soil organic compounds Cu. A glycoprotein, glomalin related soil protein (GRSP), produced in copious amounts on hyphae of arbuscular mycorrhizal fungi (AMF) sequesters toxic elements. GRSP was extracted from laboratory cultures of AMF and soils as well. It was observed that glomalin from hyphae of an isolate of Acaulospora spinosa sequestered up to 35 mg Cu/g in vitro. Thus it can be concluded that Glomalin should be considered for biostabilization leading to remediation of polluted soils.

The direct response of the external mycelium of arbuscular mycorrhizal fungi to temperature and the implications for nutrient transfer

In this study we investigated the direct effects of temperature on the extra-radical mycelium (ERM) of arbuscular mycorrhizal fungi (AMF) and the resulting impact on the host plant nutrition and biomass production. Plantago lanceolata L. plants colonized by Glomus hoi (experiment 1) and either G. hoi or Glomus intraradices (experiment 2) were grown in compartmented microcosm units. AMF hyphae, but not roots, were permitted access to a second compartment containing a 15N:13C dual-labelled organic patch maintained at different temperature treatments. All plants were maintained at ambient temperature. AMF hyphal growth in the patch compartments was relatively insensitive to temperate but results were variable. G. hoi hyphal length density was 5 times higher at ambient (c. 24 °C) than cooled (c. 11 °C) temperatures but only at the end of the first experiment (105 d after patch addition). In contrast, in the second experiment (86 d after patch addition) AMF hyphal growth was unaffected by temperature in the patch compartment. These differences between experiments are likely due to large variation among replicates in the ERM produced and differences in how the organic patch was applied. In experiment 2, plant biomass and phosphate content differed according to the temperature at which the hyphae of both AMF species grew. Plant biomass was greater when the AMF were grown at c. 18 °C than c. 11 °C but was no different at c. 21 °C. These data show that direct temperature responses by the external hyphae of AMF can independently influence associated host plant growth. However, there were also important differences between the two AMF studied both in the amount of nutrients transferred and the distribution of the nutrients.