Mycelium Of Arbuscular Mycorrhizal Fungi Research Articles

Influence of Intact Mycelium of Arbuscular Mycorrhizal Fungi on Soil Microbiome Functional Profile in Wheat under Mn Stress.

In the current agronomic context, the adoption of alternative forms of soil management is essential to increase crop yield. Agricultural sustainability requires practices that generate positive impacts and promote an increase in microbiome diversity as a tool to overcome adverse environmental conditions. An important ally is the indigenous arbuscular mycorrhizal fungi (AMF) that can improve plant growth and provide protection against abiotic stress such as metal toxicity. In a greenhouse experiment, this work studied the effect of wheat growth on several parameters of biological activity and functional microbiome in relation to wheat antecedent plant mycotrophy and soil disturbance under Mn stress. When the wheat was planted after highly mycotrophic plants and the soil was not previously disturbed, the results showed a 60% increase in wheat arbuscular colonization and a 2.5-fold increase in dry weight along with higher values of photosynthetic parameters and dehydrogenase activity. Conversely, soil disturbance before wheat planting increased the β-glucosidase activity and the count of manganese oxidizers, irrespectively of antecedent plant, and decreased drastically the wheat dry weight, the AMF colonization and the chlorophyll content compared to the undisturbed treatment. These findings suggest that not only the wheat growth but also the soil functional microbiome associated is affected by the antecedent type of plant and previous soil disturbance imposed. In addition, the improvement in wheat dry weight despite Mn toxicity may rely on shifts in biological activity associated to a well-established and intact ERM early developed in the soil.

Mycelium chemistry differs markedly between ectomycorrhizal and arbuscular mycorrhizal fungi

The chemical quality of soil carbon (C) inputs is a major factor controlling litter decomposition and soil C dynamics. Mycorrhizal fungi constitute one of the dominant pools of soil microbial C, while their litter quality (chemical proxies of litter decomposability) is understood poorly, leading to major uncertainties in estimating soil C dynamics. We examined litter decomposability of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal species using samples obtained from in vitro cultivation. We showed that the chemical composition of AM and EM fungal mycelium differs significantly: EM fungi have higher concentrations of labile (water-soluble, ethanol-soluble) and recalcitrant (non-extractable) chemical components, while AM fungi have higher concentrations of acid-hydrolysable components. Our results imply that differences in decomposability traits among mycorrhizal fungal guilds represent a critically important driver of the soil C cycle, which could be as vital as is recognized for differences among aboveground plant litter.

The arbuscular mycorrhizal fungus Rhizophagus irregularis harmonizes nuclear dynamics in the presence of distinct abiotic factors

Arbuscular mycorrhizal fungi (AMF) are widespread obligate root symbionts that assist plants in obtaining nutrients and protection against environmental stresses. In the model species Rhizophagus irregularis, heterokaryotic strains (AMF dikaryons) carry thousands of nuclei originating from two parental strains whose frequency varies depending on strains and host identity. Here, using digital droplet PCR, we demonstrate that surrounding abiotic factors (temperature, phosphorus, and pH) also change the nuclear dynamics of such strains in root organ cultures. Furthermore, when spatially separated portions of the AMF mycelium grow under different abiotic conditions, all the produced spores carry highly similar nuclear ratios. Overall, these findings demonstrate that abiotic stressors impact the nuclear organization of a widespread group of multinucleate plant symbionts, and reveal remarkable mechanisms of nuclear ratio harmonization across the mycelium in these prominent symbionts.

Impacts of arbuscular mycorrhizal fungi (AMF)on growth, N bio-fixation, and phosphorus uptake of legume crop.

To explore the effects of arbuscular mycorrhizal fungi (AMF) on the growth of legume crop, pot and field experiments with soybean were conducted. Treatments of inoculation (+AMF) and non-inoculation with AMF (-AMF) were set up for the pot experiment, and AMF mycelium non-limited and limited for the field experiment. Results of the pot experiment showed that inoculation with AMF significantly increased soybean aboveground biomass (16.5%) and root nodules number (131.4%), above-ground plant phosphorus and nitrogen concentrations and uptakes. In the field trial, the above-ground and root biomasses and root nodules number under AMF mycelium non-limited were significantly increased by 123.6%, 61.5%, and 212.5% compared with those under the limited condition, respectively. Plant phosphorus uptake, nitrogen concentration and uptake, and soil available nitrogen and phosphorus concentrations were significantly higher under AMF mycelium non-limited than the limited both in both shoot and root. Our findings provide theoretical reference for further understanding the relationship between legume crop and AMF, as well as the efficient utilization of phosphorus fertilizer.

Tolerance of arbuscular mycorrhizal fungi and microorganisms associated to their hyphosphere to aluminum in soil

Background: The elements that are toxic to arbuscular mycorrhizal fungi (AMF) and soil microorganisms, and the levels at which they affect them, are poorly known.
 Objective: To quantify the effects of: 1) aluminum added to the soil (0, 50 and 100 mg kg-1) and 2) inoculation with AMF (two isolates without prior exposure to aluminum, Acaulospora delicata and Gigaspora margarita, the native AMF community of a soil contaminated with Al, and a control without AMF) on the development of AMF mycelium and the hyphosphere-associated microbiota.
 Methods: A system with two compartments was used, a central compartment in which maize was sown and AMF were inoculated and a side compartment without root passage, where only the external mycelium was exposed to the different concentrations of Al. AMF external mycelium exposed to Al was quantified with the fatty-acid biomar-ker 16:1w5.
 Results and conclusions: Al concentrations up to 100 mg kg-1, controlling the pH of the soil, did not alter mycelium growth of any of the inoculated HMA either in the soil or in the roots. Aluminum added up to 100 mg kg-1 did not have a direct toxic effect on the growth of AMF mycelium and the hyphosphere-associated microbiota.

The Protective Biochemical Properties of Arbuscular Mycorrhiza Extraradical Mycelium in Acidic Soils Are Maintained throughout the Mediterranean Summer Conditions

In acidic soils with manganese (Mn) toxicity, arbuscular mycorrhizal fungi (AMF) can improve plant host growth by enhancing nutrition and protecting against environmental stress. The intact extraradical mycelium (ERM) of AMF is able to survive Mediterranean summer conditions and provide an earlier colonization of winter crops. This study evaluated if summer season conditions hindered the beneficial effects of wheat colonization by the intact ERM associated with a native plant, in acidic soil. Wheat was grown in soil with intact or disrupted ERM associated with Ornithopus compressus (ORN), developed for 7 or 24 weeks, to simulate ERM summer survival. The activity of antioxidant enzymes was determined, and the quantitative analysis of Mn and macronutrients was performed by inductively coupled plasma mass spectrometry (ICP-MS), in wheat shoots and respective subcellular fractions. Wheat colonization by intact ERM decreased shoot Mn concentration but increased the proportion of Mn in the apoplast. Overall, antioxidant enzymatic activity decreased but the proportion of Mn-superoxide dismutase activity over the remaining isoforms increased, suggesting its important role in the AMF-mediated mitigation of Mn toxicity. Summer conditions did not substantially reduce the benefits provided by ORN ERM. A no-till strategy allied to the development of native microbiota can contribute to the sustainable optimization of acidic soil use.

Plant carbon investment in fine roots and arbuscular mycorrhizal fungi: A cross-biome study on nutrient acquisition strategies

Comparing the belowground allocation of assimilated carbon (C) to roots and mycorrhizal fungi across biomes can reveal specific plant nutrient acquisition strategies in ecosystems and allows to predict consequences of environmental changes. Three natural ecosystems (arid shrubland, coastal matorral, humid-temperate forest) distinct in annual precipitation and vegetation cover and compositions were selected to conduct a 13CO2 pulse labeling of natural woody vegetation to chase the allocation of assimilated C to arbuscular mycorrhizal (AM) fungi and fine roots. Further, nitrogen (N) and phosphorus (P) availability, root traits, root colonization, and the extraradical AM fungal mycelium (PLFA and NLFA 16:1ω5c) were analyzed to evaluate the efficiency of nutrient acquisition strategies. AM fungal colonization decreased with increasing aridity by up to 55% intraradical and by up to 90% extraradical. High root tissue densities – indicating longevity of roots – and low specific root lengths – indicating a low nutrient uptake capacity – pointed to a slow and resource conservative acquisition strategy of plants in the arid shrubland. Plants in the matorral, on the contrary, had lower root tissue densities but higher specific root lengths and higher root N contents, pointing to a fast nutrient acquisition strategy. The expression of abundant acquisitive fine roots of plants in the matorral, however, comes at the cost of larger C investment, shown by high 13C incorporation into root tissue. High root tissue densities and greater root diameter indicated that plants in the humid-temperate forest followed a resource-conservative strategy and outsource their nutrient acquisition to AM fungi. This outsourcing provides an efficient pathway to compensate a low uptake capacity of thick and dense roots. These ecosystem-specific acquisition strategies and distinct mutualism with AM fungi across the biomes will likely affect the sensitivity of plants to abiotic and biotic stressors and, thus, ecosystem responses to future climatic and environmental changes.

Biochar and Arbuscular Mycorrhizal Fungi Play Different Roles in Enabling Maize to Uptake Phosphorus

The addition of biochar alters soil habitats and has an active effect on the symbiotic relationship between plants and mycorrhizal fungi. However, it is still unclear whether this effect alters the strategy of phosphorus uptake by plants. Therefore, pot experiments were conducted in order to investigate the effects of mycorrhizal colonization and biochar addition on plant growth, phosphorus absorption, and rhizosphere Olsen-P supply in maize under two moisture conditions—60% field water capacity (FWC) and 40% FWC. It was found that the addition of biochar increased the colonization rate of arbuscular mycorrhizal fungi (AMF), and all the addition treatments significantly improved maize biomass, peroxidase (POD) activity, chlorophyll content, photosynthetic rate (Pn), plant height, leaf area, shoot phosphorus content, and phosphorus uptake by maize under the two moisture conditions. In addition, biochar had significant effects on root morphology under both water conditions, whereas AMF only showed significant effects under water stress. In contrast, phosphatase activity and microbial activity were higher in the AMF inoculation treatment than in the biochar addition treatment, and the trend was more significant under water stress. Principal component analysis (PCA) showed that root morphology, rhizosphere microbial activity, phosphatase activity, available phosphorus content, and shoot phosphorus content had significant positive correlations. It was concluded that biochar aids plant uptake of phosphorus mainly by regulating root morphology and plant phosphorus content, whereas the large mycelium of AMF enhances microbial activity and phosphatase activity, thereby enabling more efficient phosphorus uptake by maize, especially under conditions of water stress.

Effect of arbuscular mycorrhizal fungi and mycoremediated dry olive residue in lead uptake in wheat plants

This study aims to evaluate the role of the extraradical mycelium of arbuscular mycorrhizal fungi in Pb transport. We also investigate how these fungi, alone or combined with the mycoremediated dry olive residue (MDOR), provide protection against Pb. We established a container system consisting of a central compartment and two lateral compartments separated by a hydrophobic membrane. The central compartment was filled with sterilized soil in which wheat plants, inoculated and non-inoculated with Funneliformis mosseae, were grown. The lateral compartments were filled with sterile, Pb-contaminated or MDOR-amended soil or combinations of both. In contrast to shoots and grains, wheat roots accumulated larger amounts of Pb with or without applications of MDOR. The extraradical mycelium (ERM) and the glomalin related protein content were significantly boosted by adding MDOR to Pb-contaminated soil samples. Wheat root biomass was decreased as the result of Pb contamination with no increases in plant phosphorous (P) uptake. However, MDOR, when added to Pb-contaminated soil samples, only boosted the accumulation of P in roots, with P content and biomass remaining unchanged in wheat shoots and grains. Our study highlights the role of the ERM in Pb transport its accumulation in wheat roots and how the protection effect exerted by AMF seemed to rely on MDOR application by increasing the P uptake rather than Pb.

The abundance of arbuscular mycorrhiza in soils is linked to the total length of roots colonized at ecosystem level.

Arbuscular mycorrhizal fungi (AMF) strongly affect ecosystem functioning. To understand and quantify the mechanisms of this control, knowledge about the relationship between the actual abundance and community composition of AMF in the soil and in plant roots is needed. We collected soil and root samples in a natural dune grassland to test whether, across a plant community, the abundance of AMF in host roots (measured as the total length of roots colonized) is related to soil AMF abundance (using the neutral lipid fatty acids (NLFA) 16:1ω5 as proxy). Next-generation sequencing was used to explore the role of community composition in abundance patterns. We found a strong positive relationship between the total length of roots colonized by AMF and the amount of NLFA 16:1ω5 in the soil. We provide the first field-based evidence of proportional biomass allocation between intra-and extraradical AMF mycelium, at ecosystem level. We suggest that this phenomenon is made possible by compensatory colonization strategies of individual fungal species. Finally, our findings open the possibility of using AMF total root colonization as a proxy for soil AMF abundances, aiding further exploration of the AMF impacts on ecosystems functioning.

The arbuscular mycorrhizal mycelium from barley differentially influences various defense parameters in the non-host sugar beet under co-cultivation.

The interactions between arbuscular mycorrhizal fungi (AMF) and non-host species are poorly studied. Particularly scarce is information on members of the Amaranthaceae/Chenopodiaceae family. Sugar beet (Beta vulgaris) plants were co-cultivated with a host species (Hordeum vulgare) in the presence (+AMF) or absence of Rhizophagus intraradices to explore the hypothesis that the presence of an active, pre-established AMF mycelium induces defense responses in the non-host species. Biomass of sugar beet did not respond to the +AMF treatment, while its root exudation of organic acids and phenolic acids was drastically decreased upon co-cultivation with +AMF barley. The most conspicuous effect was observed on a wide range of potential defense parameters being differentially influenced by the +AMF treatment in this non-host species. Antioxidant defense enzymes were activated and the level of endogenous jasmonic acid was elevated accompanied by nitric oxide accumulation and lignin deposition in the roots after long-term +AMF treatment. In contrast, significant reductions in the levels of endogenous salicylic acid and tissue concentration and exudation of phenolic acids indicated that AM fungus hyphae in the substrate did not induce a hypersensitive-type response in the sugar beet roots and downregulated certain chemical defenses. Our results imply that the fitness of this non-host species is not reduced when grown in the presence of an AMF mycelium because of balanced defense costs. Further studies should address the question of whether or not such modulation of defense pattern influences the pest resistance of sugar beet plants under field conditions.

Arbuscular mycorrhizal associations and the major regulators

Plants growing in natural soils encounter diverse biotic and abiotic stresses and have adapted with sophisticated strategies to deal with complex environments such as changing root system structure, evoking biochemical responses and recruiting microbial partners. Under selection pressure, plants and their associated microorganisms assemble into a functional entity known as a holobiont. The commonest cooperative interaction is between plant roots and arbuscular mycorrhizal (AM) fungi. About 80% of terrestrial plants can form AM symbiosis with the ancient phylum Glomeromycota. A very large network of extraradical and intraradical mycelium of AM fungi connects the underground biota and the nearby carbon and nutrient fluxes. Here, we discuss recent progress on the regulators of AM associations with plants, AM fungi and their surrounding environments, and explore further mechanistic insights.

Isotope Labeling to Study Phosphorus Uptake in the Arbuscular Mycorrhizal Symbiosis.

Isotope labeling enables the detection and quantification of nutrient fluxes between soil and plants through arbuscular mycorrhizal (AM) fungi. Here we describe the use of radioactive isotopes, 33P and 32P, to study the uptake of P from soil by AM fungal mycelium and its transfer to the host plant through the mycorrhizal pathway.

Associative effects of lignin-derived biochar and arbuscular mycorrhizal fungi applied to soil polluted from Pb-acid batteries effluents on barley grain safety

While disobeying environmental regulations of Pakistan, several Pb-acid batteries recycling and repairing units discharge their effluents into water canals that irrigate arable fields. Resultantly, serious ecological risks, as well as human health hazards through consumption of edible crops grown on such Pb-polluted soils have been reported. In this experiment, we observed associative effects of amending a soil polluted from Pb-acid batteries effluents (SPB) with arbuscular mycorrhizal fungi (AMF) and lignin-derived biochar (LBC) on barley grain safety to human health. The SPB was treated with AMF inoculum (a consortium of four AMF species), lignin (LN), and LBC, as sole treatments and AMF inoculum with LN and LBC. Barley parameters involving Pb distribution in grain and other parts, grain biochemistry, and nutrition were assessed. Likewise, Pb bioavailability in SPB, AMF root colonization, soil enzymes, microbial biomass carbon (MBC), and AMF produced total glomalin related soil protein (TGSP) were also scoped. Additionally, human renal cells (HEK 293) cytotoxicity test was performed by opting barley grain-related Pb concentrations. Results show that LBC + AMF significantly reduced grain Pb concentrations below the critical limit [4.67 mg kg−1 (WHO/FAO standard)], AMF colonization, MBC, soil enzymology, and TGSP, compared to control. Likewise, rest barley parameters were also improved in this treatment. Contrary to other treatments, grain produced on LBC + AMF did not result in (a) cell apoptosis, (b) cell distortion and (c) cohesion loss. Immobilization of Pb in SPB was due to the dilution effect of Pb adsorption on LBC, AMF mycelium and TGSP which resulted in a significant drop of grain Pb concentrations below the critical limit and ultimately no harm to HEK 293 cells. Our findings endorse that grain produced at LBC + AMF treatment are safer for human consumption and will not pose health risks. The LBC + AMF application can remediate SPB for safer cereal production.

Arbuscular Mycorrhizal Fungi – Their Life and Function in Ecosystem

Abstract Arbuscular mycorrhizal fungi living in the soil closely collaborate with plants in their root zone and play very important role in their evolution. Their symbiosis stimulates plant growth and resistance to different environmental stresses. Plant root system, extended by mycelium of arbuscular mycorrhizal fungi, has better capability to reach the water and dissolved nutrients from a much larger volume of soil. This could solve the problem of imminent depletion of phosphate stock, affect plant fertilisation, and contribute to sustainable production of foods, feeds, biofuel, and raw materials. Expanded plant root systems reduce erosion of soil, improve soil quality, and extend the diversity of soil microflora. On the other hand, symbiosis with plants affects species diversity of arbuscular mycorrhizal fungi and increased plant diversity supports diversity of fungi. This review summarizes the importance of arbuscular mycorrhizal fungi in relation to beneficial potential of their symbiosis with plants, and their function in the ecosystem.

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.

Effects of extreme weather events and legume presence on mycorrhization of Plantago lanceolata and Holcus lanatus in the field.

Little is known about direct and indirect effects of extreme weather events on arbuscular mycorrhizal fungi (AMF) under field conditions. In a field experiment, we investigated the response of mycorrhization to drought and heavy rain in grassland communities. We quantified AMF biomass in soil, mycorrhization of roots of the grass Holcus lanatus and the forb Plantago lanceolata, as well as plant performance. Plants were grown in four-species communities with or without a legume. We hypothesised that drought increases and heavy rain decreases mycorrhization, and that higher mycorrhization will be linked to improved stress resistance and higher biomass production. Soil AMF biomass increased under both weather extremes. Heavy rain generally benefitted plants and increased arbuscules in P.lanceolata. Drought neither reduced plant performance nor root mycorrhization. Arbuscules increased in H.lanatus several weeks after drought, and in P.lanceolata several weeks after heavy rain spells. These long-lasting effects of weather events on mycorrhization highlight the indirect influence of climate on AMF via their host plant. Legume presence increased plant community biomass, but had only minor effects on mycorrhization. Arbuscule colonisation was negatively correlated with senescence during the dry summer. Mycorrhization and biomass production in P.lanceolata were positively related. However, increased mycorrhization was related to less biomass in the grass. AMF mycelium in soil might generally increase under extreme events, root colonisation, however, is host species specific. This might amplify community shifts in grassland under climate change by further increasing stress resistance of species that already benefit from changed precipitation.

Up-regulation of genes involved in N-acetylglucosamine uptake and metabolism suggests a recycling mode of chitin in intraradical mycelium of arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal (AM) fungi colonize roots and form two kinds of mycelium, intraradical mycelium (IRM) and extraradical mycelium (ERM). Arbuscules are characteristic IRM structures that highly branch within host cells in order to mediate resource exchange between the symbionts. They are ephemeral structures and at the end of their life span, arbuscular branches collapse from the tip, fungal cytoplasm withdraws, and the whole arbuscule shrinks into fungal clumps. The exoskeleton of an arbuscule contains structured chitin, which is a polymer of N-acetylglucosamine (GlcNAc), whereas a collapsed arbuscule does not. The molecular mechanisms underlying the turnover of chitin in AM fungi remain unknown. Here, a GlcNAc transporter, RiNGT, was identified from the AM fungus Rhizophagus irregularis. Yeast mutants defective in endogenous GlcNAc uptake and expressing RiNGT took up (14)C-GlcNAc, and the optimum uptake was at acidic pH values (pH 4.0-4.5). The transcript levels of RiNGT in IRM in mycorrhizal Lotus japonicus roots were over 1000 times higher than those in ERM. GlcNAc-6-phosphate deacetylase (DAC1) and glucosamine-6-phosphate isomerase (NAG1) genes, which are related to the GlcNAc catabolism pathway, were also induced in IRM. Altogether, data suggest the existence of an enhanced recycling mode of GlcNAc in IRM of AM fungi.

Foraging capability of extraradical mycelium of arbuscular mycorrhizal fungi to soil phosphorus patches and evidence of carry-over effect on new host plant

The foraging capability of extraradical mycelium (ERM) of arbuscular mycorrhizal (AM) fungi to high soil phosphorus (P) supply and carry-over effect of ERM on new host plants remain to be explored. This study investigated whether the inhibition of ERM at high P supply varies between fungal species and whether ERM have carry-over effects when they encounter new hosts. A two-compartment device was designed to spatially separate hyphae from host roots and the carry-over effect was investigated using two-stage growth experiments. P fertilizers were applied only to hyphal compartments at a gradient of 0, 35, 150, 300, or 1,000 mg P∙kg−1. Maize plants were inoculated with Glomus mosseae, Rhizophagus irregularis or remained uninoculated. The biomass of G. mosseae in the hyphal compartment was on average higher than that of R. irregularis and the difference was greater at the second harvest. The biomass of G. mosseae increased slightly at P35 and thereafter decreased significantly with increasing P level. The biomass of R. irregularis increased slightly at P35 and did not differ significantly at higher P levels from that at P0. In general, inoculation significantly increased the biomass and P uptake of donor and receiver plants. The mycorrhizal growth responsiveness (MGR) and mycorrhizal phosphorus responsiveness (MPR) of both donor and receiver plants decreased at higher P supply level. The ratios of MGR and MPR between donor and receiver plants were close to 1 for both fungal species and were independent of P level. Inoculation with R. irregularis significantly enhanced root P uptake efficiency and alkaline phosphatase activity (ALP) in both donor and receiver plants across all P levels. Our results demonstrate that fungal species differ in their responses to soil P availability. R. irregularis was less sensitive to soil P gradients, and compensated for growth promotion and P uptake of the host by increasing ALP and root P uptake efficiency. The carry-over effects of ERM imply that the maintenance of mycorrhizal networks is of particular importance in intensive agricultural ecosystems.

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.