Sir,

Yes of course. symbiosis mechanism in AM most important as far as soil fertility is concerned. AM posses an hartig net which plays the key role in the nutrient transfer between both partners. AM root associated plants take up the nutrient like low mobile nutrients such as P, Zn. 

* The exploration on of large soil volumes by the AM in which phosphate is scavenged widely

* Fungus to keep the internal Pi concentration relatively low, so it can be easily transfer it 

* Secretion of phosphatase enzymes as well as organic acid, induces P mobilization

Even some reports show that, AM actively participated in nitrogen uptake too. Sceretions ans exudates acts on the soil particles by coating fine particles with a layer of organic matter forms micro aggregates. Micro aggregates protects the stored carbon from oxidation and keep it as a source for the rest of the beneficial microbes. with this way AM supports encourage other microbe population.

Stability of aggregates is directly related length of hyphae and to the amount of organic matter as well. 

* Do you consider , glomalin as a part of soil organic matter (SOC)?. If yes, which fraction of SOC, it could be classified?

Glomalin is an abundant soil glycoprotein and it  could sequester substantial amounts of C and N. When AM hyphae die and decompose, they leave a residue

of glomalin in the soil and directly involved in C dynamics. 

Regards

Dear Anoop,

thank you for your message.

I had the opportunity to work in subjects related to AMs in the today dissapeared Bioenergetics lab of the University of Geneva, Switzerland. At that time I was developing Biolyzer software for analysing my fluorescence curves and then my colleague, Catherine Calantzis asked me for helping her to analyse her Chl a fluorescence fast induction curves measured in Medicago sativa and Pisum sativum plants. The project was managed by Mrs Calantzis, in the framework of her PhD research work.  The director of the phd project was Prof. Gianinazzi (Dijon, France). My role was to check about the possibility to observe patterns or changes in  the fast Chl a fluorescence emission (measured at the level of leaves) about a "mycorrhization" process developing in the roots of the fungus infected (by innoculation) plants. Catherine was also investigating the role of heavy metal stress and the role of AMs. She investigated mostly cadmium enriched soil on the above mentioned plant species. My role was to help Catherine to analyse the thousands of Chl a Fluorescence curves and to decide whatever the presence of AMs was detectable with fluorescence (at the level of the leaves, with a 1 second fluorescence rise measurement). We observed and learnt many interesting facts about mycorrhizae. Yes, we can detect the effect of AM on fluorescence emission at the leaf level. Yes, we can observe the positive effect of AM on the photosynthetic behaviour of plants growing in a heavy metal polluted soil. The irony of this story is that Mrs Calantzis never akcnowledged the important role of my software, my assistance and my ideas and the many hours I expend on her project, nor in her PhD thesis nor in any of her 3 publications. She finally finished her PhD, get married to a rich swiss guy and became a nice and well educated housewife...

Later on, while working as research assistant of the Bionergetics lab of the University of Geneva (at that time prof. Strasser was the head of the lab), I directed an interesting work about soil bacteria of the genus Rhizobium sp strain NGR234 innoculated in the roots of Cowpea plants (Vigna unguiculata (L.) Walp). We developed a method to "count" the nodules in the roots of Cowpea by simply measuring Chl a fluorescence at the level of the leaves. Yes, that it's possible also.

While working on those projects I had to read a lot about AM's and Rhizobia mainly related to leguminous plants.

From those experiences I can say: Yes, absolutely, AM's are important. They help to fix important nutrients for the plant. They can become a kind of buffer for absorbing heavy metal from polluted soil, rhizobia absorbs nitrates and fix nitrogen in soil...

I will try to answer your questions as soon as I have some free time.

Best regards

Ronald

Dr Anoop Sir,

Thanks for initiating the discussion. I am waiting to learn from the response from my colleagues. In this part, few works on AM started during 1990s but we had not learned more thereafter. Currently, microbiologists have started work on the aspect and the results are expected to be in public shortly. During presentation of their preliminary work the results appeared encouraging, especially on disease resistance.

Thanks and regards

Dear Dr Anoop Ji,

This is what we could gather from exising literature.

Mode of action

PRESYMBIOSIS

The development of AM fungi prior to root colonization, known as presymbiosis, consists of three stages: spore germination, hyphal growth, host recognition and appressorium formation.

Spores of the AM fungi are thick-walled multi-nucleate resting structures. The germination of the spore does not depend on the plant, as spores have been germinated under experimental conditions in the absence of plants both in vitro and in soil. However, the rate of germination can be increased by host root exudates. AM fungal spores germinate given suitable conditions of the soil matrix, temperature, carbon dioxide concentration, pH, and phosphorus concentration.

The growth of AM hyphae through the soil is controlled by host root exudates and the soil phosphorus concentration.

Low-phosphorus concentrations in the soil increase hyphal growth and branching as well as induce plant exudation of compounds that control hyphal branching intensity.

The branching of AM fungal hyphae grown in phosphorus media of 1 mM is significantly reduced, but the length of the germ tube and total hyphal growth were not affected. A concentration of 10 mM phosphorus inhibited both hyphal growth and branching. This phosphorus concentration occurs in natural soil conditions and could thus contribute to reduced mycorrhizal colonization.

Root exudates from AMF host plants grown in a liquid medium with and without phosphorus have been shown to effect hyphal growth. Pre-germinated surface-sterilized spores of Gigaspora magarita were grown in host plant exudates. The fungi grow in the exudates from roots starved of phosphorus had increased hyphal growth and produced tertiary branches compared to those grown in exudates from plants given adequate phosphorus. When the growth-promoting root exudates were added in low concentration, the AM fungi produced scattered long branches. As the concentration of exudates was increased, the fungi produced more tightly clustered branches. At the highest-concentration arbuscules, the AMF structures of phosphorus exchange were formed.

This chemotaxic fungal response to the host plants exudates is thought to increase the efficacy of host root colonization in low-phosphorus soils. It is an adaptation for fungi to efficiently explore the soil in search of a suitable plant host.

Further evidence that AM fungi exhibit host-specific chemotaxis: Spores of Glomus mosseae were separated from the roots of a host plant, nonhost plants, and dead host plant by a membrane permeable only to hyphae. In the treatment with the host plant, the fungi crossed the membrane and always emerged within 800 µm of the root. Whereas in the treatments with nonhost plants and dead plants, the hyphae did not cross the membrane to reach the roots.

This demonstrates that arbuscular mycorrhizal fungi have chemotaxic abilities that enable hyphal growth toward the roots of a potential host plant.

Molecular techniques have been used to further understand the signaling pathways that occur between arbuscular mycorrhizae and the plant roots. In the presence of exudates from potential host plant roots, the AM undergoes physiological changes that allow it to colonize its host. AM fungal genes required for the respiration of spore carbon compounds are triggered and turned on by host plant root exudates. In experiments, there was an increase in the transcription rate of 10 genes half-hour after exposure and an even greater rate after 1 hour. A morphological growth response was observed 4 hours after exposure. The genes were isolated and found to be involved in mitochondrial activity and enzyme production. The fungal respiration rate was measured by O2 consumption rate and increased by 30% 3 hours after exposure to root exudates. This indicates that AMF spore mitochondrial activity is positively stimulated by host plant root exudates. This may be part of a fungal regulatory mechanism that conserves spore energy for efficient growth and the hyphal branching upon receiving signals from a potential host plant.

When arbuscular mycorrhizal fungal hyphae encounter the root of a host plant, an apressorium (an infection structure) is formed on the root epidermis. The apressorium is the structure from which the hyphae can penetrate into the host’s parenchyma cortex. The formation of apressoria does not require chemical signals from the plant. AM fungi could form apressoria on the cell walls of “ghost” cells in which the protoplast had been removed to eliminate signaling between the fungi and the plant host. However, the hyphae did not further penetrate the cells and grow in toward the root cortex, which indicates that signaling between symbionts is required for further growth once appresoria are formed.[

Symbiosis

Once inside the parenchyma, the fungi forms highly branched structures for nutrient exchange with the plant called "arbuscules". These are the distinguishing structures of arbuscular mycorrhizal fungus. Arbuscules are the sites of exchange for phosphorus, carbon, water, and other nutrients. There are two forms: Paris type is characterized by the growth of hyphae from one cell to the next; and Arum type is characterized by the growth of hyphae in the space between plant cells. The choice between Paris type and Arum type is primarily determined by the host plant family, although some families or species are capable of either type.

The host plant exerts a control over the intercellular hyphal proliferation and arbuscule formation. There is a decondensation of the plant's chromatin, which indicates increased transcription of the plant's DNA in arbuscule-containing cells. Major modifications are required in the plant host cell to accommodate the arbuscules. The vacuoles shrink and other cellular organelles proliferate. The plant cell cytoskeleton is reorganized around the arbuscules.

There are two other types of hyphae that originate from the colonized host plant root. Once colonization has occurred, short-lived runner hyphae grow from the plant root into the soil. These are the hyphae that take up phosphorus and micronutrients, which are conferred to the plant. AM fungal hyphae have a high surface-to-volume ratio, making their absorptive ability greater than that of plant roots. AMF hyphae are also finer than roots and can enter into pores of the soil that are inaccessible to roots. The third type of AMF hyphae grows from the roots and colonizes other host plant roots. The three types of hyphae are morphologically distinct.

Nutrient uptake and exchange

AMF are obligate symbionts. They have limited saprobic ability and are dependent on the plant for their carbon nutrition. AM fungi take up the products of the plant host’s photosynthesis as hexoses.

The transfer of carbon from the plant to the fungi may occur through the arbuscules or intraradical hyphae. Secondary synthesis from the hexoses by AM occurs in the intraradical mycelium. Inside the mycelium, hexose is converted to trehalose and glycogen. Trehalose and glycogen are carbon storage forms that can be rapidly synthesized and degraded and may buffer the intracellular sugar concentrations.[19] The intraradical hexose enters the oxidative pentose phosphate pathway, which produces pentose for nucleic acids.

Lipid biosynthesis also occurs in the intraradical mycelium. Lipids are then stored or exported to extraradical hyphae where they may be stored or metabolized. The breakdown of lipids into hexoses, known as gluconeogenesis, occurs in the extraradical mycelium. Approximately 25% of the carbon translocated from the plant to the fungi is stored in the extraradical hyphae. Up to 20% of the host plant's photosynthate carbon may be transferred to the AM fungi. This represents a considerable carbon investment in mycorrhizal network by the host plant and contribution to the below-ground organic carbon pool.

An increase in the carbon supplied by the plant to the AM fungi increases the uptake of phosphorus and the transfer of phosphorus from fungi to plant (Bücking & Shachar-Hill 2005). Phosphorus uptake and transfer is also lowered when the photosynthate supplied to the fungi is decreased. Species of AMF differ in their abilities to supply the plant with phosphorus. In some cases, arbuscular mycorrhizae are poor symbionts, providing little phosphorus while taking relatively high amounts of carbon.

The benefit of mycorrhizae to plants is mainly attributed to increased uptake of nutrients, especially phosphorus. This increase in uptake may be due to increase surface area of soil contact, increased movement of nutrients into mycorrhizae, a modification of the root environment, and increased storage. Mycorrhizae can be much more efficient than plant roots at taking up phosphorus. Phosphorus travels to the root or via diffusion and hyphae reduce the distance required for diffusion, thus increasing uptake. The rate of inflow of phosphorus into mycorrhizae can be up to six times that of the root hairs. In some cases, the role of phosphorus uptake can be completely taken over by the mycorrhizal network, and all of the plant’s phosphorus may be of hyphal origin.

The available phosphorus concentration in the root zone can be increased by mycorrhizal activity. Mycorrhizae lower the rhizosphere pH due to selective uptake of NH4+ (ammonium-ions) and release of H+ ions. Decreased soil pH increases the solubility of phosphorus precipitates. The hyphal uptake of NH4+ also increases the flow of nitrogen to the plant as NH4+ is adsorbed to the soil's inner surfaces and must be taken up by diffusion.

Scope of application

Mycorrhiza plays a very important role on enhancing the plant growth and yield due to an increase supply of phosphorus to the host plant. Mycorrhizal plants can absorb and accumulate several times more phosphate from the soil or solution than non–mycorrhizal plants. Plants inoculated with endomycorrhiza have been shown to be more resistant to some root diseases.

Endomycorrhizas

Diagrammatic representation of the main cellular features of the arbuscular endomycorrhiza. Hyphae from a germinating spore infect a root hair and can grow within the root between

root cortical cells and also penetrate individual cells, forming arbuscules.

These are finely branched clusters of hyphae, which are thought to be the major site of nutrient exchange between fungus and plant.

[Mark Brundrett’s website at http://mycorrhizas.info. Figure & caption from Moore et al., 2011 ]

The demarcation of endomycorrhizas from ectomycorrhizas is by no means as sharp and clear as may be assumed from the definition given at the beginning of this topic. Numerous fluid transitions exist and often changes an ectomycorrhiza into an endomycorrhiza. Such cases have been termed ecto-endomycorrhizas. V/A-mycorrhizas are by far the most common types as has been mentioned before. Before going into more detail, two other manifestations, the mycorrhizas of Ericales and that of orchids have to be introduced.

Ericales, and especially species of the Ericaceae-family are in nature always associated with fungi. They are therefore regarded as obligatorily mycotrophic. This does not mean that Ericaceae cannot be cultivated without fungi. Calluna, Vaccinum, azaleas and others grow just as well when cultivated on a purely inorganic substrate as in nature together with fungi. If organic material (peptone or yeast extract, for example) is added to the nutrient medium, however, growth is strongly inhibited. It seems that the roots secrete substances that react with organic material and form toxins. These toxins are deactivated in the presence of fungi. In other words: growth on nutrient-rich soils is optimal in the presence of mycorrhizal fungi. Ericaceae, however, occur almost only on acidic soils extremely poor in nutrients (oligotrophic). The advantage of the obligatory association with fungi allows them to use even these soils efficiently. The fungus attack occurs in a number of species shortly above the vegetative point. Calluna’s primary vegetative point, however, is destroyed by the fungus, and as a consequence secondary vegetative zones are activated causing an increase in the root system’s number of branchings and thus a better penetration of the soil.

It is problematic to afforest Calluna expanses, since the mycorrhizal fungi that forest trees need are lacking. The lack exists due to inhibiting substances, that are secreted by the mycorrhizal fungi that socialize with Calluna. Experiments showed, that extracts from Calluna-humus inhibit the mycelium growth of many fungi. Only a few species like Boletus scaber and Amanita muscaria are resistant. Both species occur everywhere as mycorrhizal fungi where birches begin to penetrate Calluna expanses.

A phenomenon similar to the Ericaceae-mycorrhizas occurs in pinesap (Monotropa), a saprophytic plant devoid of chloroplasts as well as in different species of (green) Pyrolaceae. Monotropa is a root parasite growing on various deciduous trees and conifers. Its root is wrapped in a dense fungus mycelium that penetrates not only the surrounding soil, but also the roots of the host trees thus making an indirect contact between host and parasite. F. FRANCIS and D. J. READ (1984) verified experimentally with the example of a V/A-mycorrhiza that such bridges lead indeed assimilates.

They planted radioactively labelled seedlings of Plantago major together with non-labelled ones of Festuca ovina into a culture container. In a further experiment, Plantago was inoculated with a fungus. The root systems of both species are easily distinguished morphologically. The radioactivity spreads both in the fungus and in Festuca ovina after a short culture period in the container, while the roots of Festuca ovina remained unlabelled despite of the direct physical contact with the labelled Plantago-roots in the fungus-free culture.

Orchidaceae are obligatory mycotrophic just like Ericaceae. Their causes differ, though (H. BURGEFF, 1909, 1936). Orchid seeds are extremely small (0.3 – 14 µm). They have usually no cotyledons which means that a seed can germinate but not develop further than to a few-celled state. Further development is possible only in association with fungi that provide the nutrient substratum. Orchids are accordingly parasites if only in the first phase of their life. Many of them (those with green leaves) change to an autotrophic life during a later stage of development. The fungus becomes superfluous.

The mycorrhizal fungus penetrates the tissue of the young seedling (usually through the suspensor), from where it spreads into the developing root. Shoot and root tuber (if present) are generally not infected.

The endotrophic fungi do usually perish in the course of the plant’s development and their remains are absorbed by the orchids. If this host-specific action does not take place, then the fungus spreads and becomes parasitic. That is why only a small percentage of seedlings develops in many orchid species. The inhibition of the fungus growth is caused by the synthesis of an antagonist that was at first named orchinol, and was later characterized as dehydroxyphenanthrin by E. GÄUMANN and H. KERN (1959). This fungicide has an effect on numerous mycorrhizal and terrestrial fungi. Its synthesis is only induced in the presence of the fungus.

Mycorrhiza increase root surface area for water and nutrients uptake. The use of mycorrhizal biofertilizer helps to improve higher branching of plant roots, and the mycorrhizal hyphae grow from the root to soil enabling the plant roots to contact with wider area of soil surface, hence, increasing the absorbing area for water and nutrients absorption of the plant root system. Therefore, plants with mycorrhizal association will have higher efficiency for nutrients absorption, such as nitrogen, phosphorus, potassium, calcium, magnesium, zinc, and copper; and also increase plant resistance to drought.

Benefits of mycorrhizal biofertilizer can be summerised as follows:

1. Allow plants to take up nutrients in unavailable forms or nutrients that are fixed to the soil. Some plant nutrients, especially phosphorus, are elements that dissolve were in water in neutral soil. In the extreme acidic or basic soil, phosphorus is usually bound to iron, aluminum, calcium, or magnesium, leading to water insolubility, which is not useful for plants. Mycorrhiza plays an important role in phosphorus absorption for plant via cell wall of mycorrhiza to the cell wall of plant root. In addition, mycorrhiza helps to absorb other organic substances that are not fully soluble for plants to use, and also help to

absorb and dissolve other nutrients for plants by storage in the root it is associated with.

2. Enhance plant growth, improve crop yield, and increase income for the farmers. Arising from improved water and essential nutrients absorption for plant growth by mycorrhiza, it leads to improvement in plant photosynthesis, nutrients translocation, and plant metabolism processes. Therefore, the plant has better growth and yield, reduce the use of chemical fertilizer, sometimes up to half of the suggested amount, which in turn increases income for the farmers.

3. Improve plant resistance to root rot and collar rot diseases. Mycorrhizal association in plant roots will help plant to resist root rot and collar rot diseases caused by other fungi.

4. It can be used together with other agricultural chemicals. Mycorrhiza are endurable to several chemical substances; for example; pesticide such as endrin, chlordane, methyl parathion, methomyl carbofuran; herbicide such as glyphosate, fuazifopbutyl; chemical agents for plant disease elimination such as captan, benomyl, maneb triforine, mancozeb and zineb.

Best Regards

Vijay

Dear Anoop Kumar Srivastava,

The fertility of the soil - the soil's ability to meet the needs of plants in the power elements, moisture and air, as well as to provide conditions for their normal life. It is an emergent property of the soil. The interaction of the components of soil fertility appears. The soil comprises humus, water, air, sand, and clay. At its fertility significantly affects the content of nitrogen, phosphorus, potassium salts and other substances.

From ancient times, people evaluate the soil mainly in terms of its fertility. It depends on the fertility of crops.

Soil - a complex system that lives and develops by its own laws, so a fertility need to understand the entire range of soil properties and processes that determine the normal development of plants. All of the processes occurring in the soil, linked. An exception or attenuation of any constituent leads to a change in the entire structure of the soil and loss of its qualities. Soil degradation - a chain reaction, which is difficult to stop. Deterioration of land reduces the productivity of plants. The soil in this case, it becomes susceptible to erosion and leaching of nutrients, which in turn leads to a decrease in the number of plants. Events for the resumption of long-term fertility of soils is very costly and complex, so it is important to monitor the condition of the soil, preventing its severe depletion or pollution.

To determine the fertility of the soil is necessary to pay attention to its composition, the acidity, the ratio of water and oxygen. With observation and a basic knowledge of biology can determine the condition of the soil and to take the necessary measures to improve or maintain soil properties.

Regards, Shafagat

 Dr. Annor, very interesting questions. We are beginning a Research in potato with micorrizas and looking forward some information are surely will take attention in the answers of researchers. Thanks!

Sergio 

 A relevant question, I delivered a credit seminar when I was Ph.D. student on this topic.  We know that Arbuscular Mycorrhizal Fungi (AMF) constitute a group of root obligate biotrophs that exchange mutual benefits with about 80% of plants. They are considered natural biofertilizers, since they provide the host with water, nutrients, and pathogen protection, in exchange for photosynthetic products. Thus, AMF are primary biotic soil components which, when missing or impoverished, can lead to a less efficient ecosystem functioning. The process of re-establishing the natural level of AMF richness can represent a valid alternative to conventional fertilization practices, with a view to sustainable agriculture. The main strategy that can be adopted to achieve this goal is the direct re-introduction of AMF propagules (inoculum) into a target soil.

Let us have look on following points:

I totally agree with Dr Suresh K Malhotra that the usefulness of the symbiosis of VAM will be host species specific.

Thank you for initiating this discussion. Its very helpful and informative. I am really learning and getting ideas.

Thanks for initiating some wonderful discussion ..

Shafagat , good point to look at better input-use-efficiency , AMs hold a good promise in that direction...

Gobinath, some exciting thoughts , aggregate stability , this is one of the most pronounced glueing  effects of AMs through ecto-mycorrhizal mycelial networking ..another good point to see beyond phosphorous nutrition, nutrients like Fe, Mn, Zn also are mobilised so effectively through AMs networking..

Ronald , so happy to see complete profile of AMs functioning like  salt removal issue, compatibility of rhizobium with AMs , a rather new field..worth debating further...

Sergio, thanks fro giving some clue..potato could one crop , highly depenedent upon Ams.

Dr Malhotra, i agree with you , in order to exploit the efficiency of AMs , which is purely  AM species and type of host dependent , since mycorrhizal colonization would be severely affected if we do not take into account such issues....appreciating further participation of  Vijayaraghavan about the host specificity...

Saidu, many thanks for appreciating ..i always say , its a joint effort...

Let start the some theme questions. How do AMs communicate with host plant ..? Have been able to decode the signaling communication between variety of  AMs and host plant ..?

VA-mycorrhiza (VAM fungi) when used as Biofertilizers enhance uptake of P, Zn, S and water, leading to uniform crop growth and increased yield and also enhance resistance to root diseases and improve hardiness of transplant stock.They liberate growth promoting substances and vitamins and help to maintain soil fertility. Are there reports about the quantification of growth promoting substances and how it is mobilized in the plant system. Can we regulate it. 

I consider AMF much different than rest of the soil microbial communities due to their ability to perform and contribute to multiple soil fertility functions.

The nature of the mycorhizal fungal symbiont is different that the roles of rhizosphere bacteria. The ability of fungi to search and multiply the surface are of the plant is not captured by any bacteria in my opinion. The soil contacted by the mycosymbiont far exceeds thant contacted by botanical roots lacking the fungal partner. The amazing glistening exudation of glycoprotein like substances which are able to give a protective water repellency and have a high content of iron in its structure is something also not paralleled in other microbial groups. The resistance of glomalin the mycorrhizal glycoprotein makes it a good for stabilizing soil Carbon and Nitrogen and allows accrediting of these greenhouse gas contributors to be retained rather than lost to the atmosphere. In the tripartite idea of synergetic symbiosis the combinations of host plants mycorrhizae and rhizosphere bacteria all play primary roles in creating the health soil root environment.

Yes Anoop Ji, VAM is different from other biofertilizers for soil fertility role. Many of our RG colleagues have described this aspect in detail. But VAM is different from other biofertilizers from application point of view as well as from storage of culture point view. I am enumerating few differences for knowledge sake, hope you all will like it. Mycorrhiza is a fungal biofertilizer All others are bacterial biofertilizers. Mycorrhiza is applicable to a wide range of plants from floricultural, horticultural, silivicultural, to agricultural species including legumes, tree and plant species, except a few like mustard (Brassica sp.) and  Sugar beet (Beta vulgaris). Other biofertilizers, products are not specific to crops or plant type. Mycorrhiza has easy storage at ambient temperature. Other biofertilizers require low temperature for storage hence are cost ineffective. Mycorrhiza has prolonged shelf life at room temperature. Other biofertilizers shelf life is limited under strict condition of maximum storage

At IRRI we tried with mycorrhiza-rice association; unfortutanely faield to have benefit. This could be due to nature of rice plant and crop culture.

Nearly all phytohormones are employed by plants to regulate the symbiosis with AM fungi, but the regulatory role of cytokinin (CK) is not well understood.

Important for the signaling of symbiosis is the ability of plants under deficient Phosphorus availability to secrete Strigolactones. These Strigolactones are derived from plant carotenoid terpenoids. When secreted into the soil these Strigolactones stimulate the growth and development of arbuscular mycorrhizal fungi. This is type of chemical communication plant to fungus to plant.  Plants with high Phosphorus availability do not signal the mycorrhizal symbiosis and are less likely to develop extensive symbiosis.

The extensive growth of mycorrhizal fungi usher a change in the metabolism of the plant improving many stress reactions including defense reactions.

Besides better stress reactions, the longer term benefit of the association is the increased ability to stimulate Carbon sequestration and the capacity of mycorrhizae to favor critical soil aggregation.

In addition, the information would suggest in legumes the Rhizobium biological nitrogen fixation and the mycorrhizae can interact synergistically and greatly reduce the "need" from synthetic fertilizer inputs which have energetic, economic and environmental issues associated with them. 

In maize and many other crops about one half of the energy and Carbon footprint comes from Nitrogen fertilization. Symbiosis can greatly reduce the requirement for both Nitrogen and Phosphorus and can result in better crop yield stability and cropping system sustainability. 

The plants in our agricultural production system are the primary producers. They as plants are in turn are recycled by microbes mostly the bacteria and fungi.. Without decomposers the nutrient cycles will not be complete its circle or cycle but rather result in losses to the environment the broken circle a sign of environmental degradation.

The symbiosis of plant with AM fungus is described as mutual feeding plants giving fungus C or carbohydrate and the fungus giving the plant Phoshate other minerals critical water and in this mixture the soil is fed. Health symbiosis favor the overall biological activity of the soil community. This is a sign of healthy and productive soils. 

The work on legumes show that when plants harbor vibrant mycorrhizal roots the root can be better colonized with Rhizobium bacteria. In this three part or tripartitate symbiosis the decomposer group and the consumer group such as the microbes and animals they all flourish.

In an agricultural system cereals combined with pulses increases the productivity quality and health of the humans, animals, and decomposers. Synergist symbionts are keys for this system to flourish. We come to the conclusion that this health is result of the synergistic and symbiotic interactions found in nature and need to be preserved in agricultural systems that foster high productivity and the building rather that the destruction of the soil our agricultural system ultimately depends upon. 

Rejuvenation of soil by mycorrhizal fungi are shown is several cases. In areas of mine spoils the use of mycorrhizae are a prerequisite for this come back. The natural soil productivity is found in the top soil the subsoil is more absent for critical biology. As agricultural systems focused on grass and legumes the perennial deep rooted species drive the mycorrhizal and biological in both the top and subsoil areas. When soil is sterilized the productivity for soils can crash. This result is only apparent when sterilized soil is re-inoculated with mycorrhizae. Because the mycorrhizae are both pervasive the effects of their action is only available under specialized investigation. Michael Melendez has demonstrated that desert environments can support luxury growth of trees when humic materials are combined with mycorrhizae. Another case study is the over 34 year Farming Systems Trial of the Rodale Institute show that biologically based management lift the yield potential of the farming system as the soil organic matter increases and at the same time the mycorrhizae components increases throughout the soil profile. Since the glomalin like substances are notably resistant to decay this helps give the mechanism for the rejuvenation noted in the soil. 

Do you feel, AMs could improve the plant preparedness to fight against salinity and drought?

Yes I definitely believe that Arbuscular Mycorrhizae can improve the preparedness for plants to combat drought and salinity. Since the area of a highly mycorrhizal plant has hundreds to thousands of times more compact with the soil reserve of water it can tap into a much greater proportion of availability water reserved in soil.  In relation to salinity the symbiotic plant has more ability to resist salinity may well be related to stimulation of plant symbiotic because of an enhancement of antioxidant activity which can increase greatly under saline exposure.

* Do you consider , glomalin as a part of soil organic matter (SOC)?.Again I do believe this. The fraction of SOC, it could be classified? Here again I would say glomalin is an important component of Soil Organic Carbon. In this area the materials are qualified as an extraction procedures. As such none of the components are single natural substances but rather a hetereogeneous complex mixture. In soil organic matter analysis the components such as 1) fulvic acid, 2) humic acids and 3) humins are definitely not a single substances has made the investigation of the materials somewhat more difficult to interpret and decipher.  While the fulvic acids which are more able to mobilize nutrients as chelates than Humins the recycling times of Humins and glomalin substance the more refractory materials are critical in the sense of water relationship as they stick in the environment and accumulate and lead to greater ability to improve soil porosity, percolation but also water capture retention and use. 

Do you consider AMs, different than rest of the soil microbial communities for multiple soil fertility functions ?  : Yes.I believe of the two greatest microbial groups the fungi are so importantly different based on networking natural of the mycelium body and growth. This is fundamentally different that bacterial masses which lack that structure and cohesiveness. In reality it is somewhat difficult to separate any of these for by their nature their interact in a linked community. 

Paul some excellent responses. How can we separate the functionality of OC deposited by hyphal network of AMs. How do AMs contribute to maintenance of non labile pool of OC?

Dear Sikha Deka, I believe there is a lot of positive correlation or association between the fulvic, humic, humin and glomalin related substances. What is not necessarily correlated is primary plant productivity and equilibrium amounts of Soil Organic Carbon or Nitrogen gained in the soil. Fertilizer interest previously suggested that just increasing the primary plant productivity would automatically sustain and increase soil reserves but this has not been the case in much research for example the analysis of Morrow Plots at University of Illinois showing high productivity and decreasing soil Nitrogen and Carbon values. For this reason we need to have longer term thinking and look for accrual, stability and degenerative practices. My strong guess is that AM contributes both to labile and non labile forms of soil organic matter. In the long term Rodale Farming Systems Trial the increase in mycorrhizae fungi measured by spore amounts and diversity preceded the the increasing of Soil Carbon and Nitrogen amounts.. These measures showed significant difference before increases in Soil Carbon and Nitrogen were detectable. In this vein the mycorrhizal analysis can be pre-indication of coming conclusive positive changes in the soil resource capacity. Mycorrhizae need to analyzed for their bioindication potential. 

Yes Paul, you are not wrong. VAM contributes very effectively and labile carbon makes up a fraction of the total carbon pool. It breaks down relatively quickly, and is an active source of nutrition. It is an indicator of change in the soil. Labile carbon is the major food source for soil microbes. The size and quality of the labile carbon pool influences the decomposition rate.

Paul, how does resilience time carbon deposited by AMs differ from organic manures?

Dear Sikha Deka, If we look at organic manures we need to separate compost from manure. Manures can be readily available for nutrient but they do not show much ability to increase long term soil Carbon. They can prevent losses of soil organic matter but do not conclusively add to the reserves over the long term. In terms of compost the readily availability of nutrients is less but the ability to conclusively build the soil organic matter is more. The abilty of cover crops to increase soil organic matter is more than raw manure and less than composts. The ability of soil organic matter to increase from the cover cropping or by forage cropping is related to a better ability to increase and maintain mycorrhizal activity and its effect to increase soil Carbon values. One of the best practices for both mycorrhizae and soil carbon is the rotation of the forage and hay perennial species based on mixed grass, legume and even composites with stimulate abundant diverse mycorrhizae. Hope this gives some useful information. 

Why most the crops belonging to family Chenopodiaceae and Brassicaceae are least AM dependent. What are the factors that decide the crop responses to mycorrhization.

 AM fungi are particularly important in improving uptake of Phosphorous because of the very short transmission distance of phosphate ions in the soil. They also enhance the uptake of secondary and micro-nutrients including calcium, sulphur, zinc and copper. Most agricultural crops can perform better and are more productive when they are well colonized by AM Fungi inoculation of plant roots with AM. Fungi has also been reported to enhance phytoaccumulation of heavy metals such as zinc, cadmium, arsenic and selenium

1. AM communicate via plants through certain exudates released by plants. Moreover, there are certain hormones they play a role in it and as widely known the phosphorous and carbon levels also work as signals.

2. I am sot sure if they encourage the density of other microorganisms but yes their performance is never compromised in presence of other organisms.

3. Yes, they are more effective in improving the carrying capacity of soil as they improve the soil quality and water holding capacity of soil.

4. It works as a very effective biological amendment.

5. It can very well improve plant preparedness; the term here is known as priming mechanism.

6. Glomalin forms a part of soil organic matter.http://mycorrhizae.com/wp-content/uploads/2013/03/Building-Organic-Matter-Biologically-PDF.pdf. This is a good article regarding that.

Hope this helps.

Thank you

An excellent responses,  Dr Malhotra and Miss Ami , appreciate both of you . what do you feel, glomaline over time is diverted to non-labile pool of soil organic matter..? 

Paul , hats off to you for steering such an educative discussion ... 

Dear Anoop! You're right. Concise answers to the essence of the problem should dominate in the scientific community. Dr Malhotra and Miss Ami beautifully demonstrated this postulate of science. Viva science!

Thanks for compliments to Vladimir. We know that mycorrhizal spores, pieces of colonized crop roots & viable mycorrhizal hyphae function as active propagules of VAM fungi that can be used as inoculum to infect other plants with AM fungi. But developing a low-cost procedure and identifying features to maximize propagule production needs thrust.

On-farm production of inoculum of indigenous arbuscular mycorrhizal fungi and assessment of diluents of compost for inoculum production.

Douds DD Jr1, Nagahashi G, Hepperly PR.

Author information

Dear Suresh, Enclosed is a low cost method we utilized in joint USDA and Rodale Institute to produce AM Fungal increase. This type of approach is adaptable through the World.

Abstract

On-farm production of arbuscular mycorrhizal [AM] fungus inoculum can be employed to make the benefits of the symbiosis more available to vegetable farmers. Experiments were conducted to modify an existing method for the production of inoculum in temperate climates to make it more readily adoptable by farmers. Perlite, vermiculite, and peat based potting media were tested as diluents of yard clippings compost for the media in which the inoculum was produced using bahiagrass (Paspalum notatum Flugge) as host plant. All produced satisfactory concentrations of AM fungus propagules, though vermiculite proved to be better than potting media (89 vs. 25 propagules cm(-3), respectively). Two methods were tested for the growth of AM fungi indigenous to the farm: (1) adding field soil into the vermiculite and compost mixture and (2) pre-colonizing the bahiagrass seedlings in media inoculated with field soil prior to transplant into that mixture. Adding 100 cm(3) of field soil to the compost and vermiculite produced 465 compared to 137 propagules cm(-3) for the pre-colonization method. The greater flexibility these modifications give will make it easier for farmers to produce inoculum of AM fungi on-the-farm.

Hope you find the information helpful for your efforts. 

Thank you Dr. Paul for very useful information. Production of VAM propagules at satisfactory level, protocols are available.

Dear Suresh This is an indication that although in a theoretical sense the major constraints are addressable the big problem is that for the most part we have a problem with programmatic application of our knowledge to address the constraints on applied levels of the farmer fields. Many times farmers are way ahead with their ability to apply things but do not have the knowledge and tools to implement them. For this reason the combination of Extension, Teaching and Applied and Basic research is such a fundamental issue in our global educational efforts. Some thoughts and thanks for your appreciation your participation in discussing the issues and concerns put forward. Sincerely, Paul 

Good points Dr. Paul. Yes it is true, technology is available but needs to be transferred to beneficiary.

Thanks friends for some excellent stuff, i was out of touch for few days , hope , i will catch up as you keep on providing your on par intellect on the issue concerning  AMFs. Let me initiate some discussion with role of AMFs in combating abiotic stress. Here is one good work, the abstract of which is given below: 

Citrus is one of the most widely cultivated fruit crops, whose rhizosphere inhabits a class of beneficial fungi, popularly known as arbuscular mycorrhizal fungi (AMF). Different species of AMF viz., Acaulospora, Entrophospora, Gigaspora, Glomus, Pacispora, Sclerocystis, and Scutellospora have been observed to colonize citrus roots for the formation of arbuscular mycorrhizal (AM) symbiosis, where both the symbiotic partners are mutually benefited (up to 20% of photosynthetic carbohydrates from the host plant is diverted toward the growth of AM, in the exchange of water and nutrient uptake from the fungal partner to the host plant). AM symbiosis can usually confer better plant growth, higher nutrient uptake, greater tolerance to abiotic and biotic stresses, and soil structure improvement in the host plant. Meanwhile, AM-inoculated citrus plants have shown greater tolerance to drought stress (DS). Drought stress strongly restricted both the development of non-AM-citrus and the mycorrhizal development of AM-citrus, but AM colonization produced a positive effect on plant growth and photosynthesis, even under DS. This review provides an overview of possible mechanisms involved in DS tolerance through improved water and nutrient uptake (especially P nutrition) using extraradical hyphal growth; effective spatial configuration of root system; elevated concentration of tetramine spermine; osmotic adjustment through non-structural carbohydrates, K+, Ca2+, and Mg2+, but not proline; scavenging reactive oxygen species through antioxidant enzymes and antioxidants; and glomalin-bound soil structural improvements, besides, some new exciting perspectives including water transport by mycorrhizal hyphae and molecular analysis are suggested. PDF enclosed fro further  reading 

Arbuscular Mycorrhizal Fungi (AMF) constitute a group of root obligate biotrophs that exchange mutual benefits with about 80% of plants. It is well proved VAM are natural biofertilizers, provide host with water, nutrients, and pathogen protection, in exchange for photosynthetic products. I am reiterating few of same points which I am replied her also. Originally, AMF were described to generally lack host- and niche-specificity, and therefore suggested as agriculturally suitable for a wide range of plants and environmental conditions.Unfortunately, the assumptions that have been made and the results that have been obtained so far are often worlds apart. The problem is that success is unpredictable since different plant species vary their response to the same AMF species mix. Many factors can affect the success of inoculation and AMF persistence in soil, including species compatibility with the target environment, the degree of spatial competition with other soil organisms in the target niche and the timing of inoculation. Hence these factors are required to be taken into account when “tuning” an inoculum to a target environment. 

How do AMs serve towards ecosystem service beyond soil fertility?

Nice question Dr Deka , and ably responded by Abhishek , as usual...

AMF are also responsible for other services that favour the plants they colonize: (a) they positively affect plant tolerance towards both biotic (e.g., pathogens) and abiotic stresses (i.e., drought and soil salinity) by acting on several physiological processes, such as the productionof antioxidants, the increment of osmolyte production or the improvement of abscisic acid regulation , and the enhancement of plant tolerance to heavy metals ; (b) they help plants become established in harsh/degraded ecosystems, such as desert areas and mine spoils ; (c) they increase the power of phytoremediation (the removal of pollutants from the soil by plants) by allowing their host to explore and depollute a larger volume of soil . Another crucial ecological role played by AMF is their capacity to directly influence the diversity and composition of the aboveground plant community.

 Other studies confirmed that plant species richness can be altered not only by climatic and edaphic factors, but also by soil microbial assemblages. The underlying mechanism is not completely understood, but could be related to the promotion of seedling establishment of secondary plant species . Nevertheless, on some occasions, AMF can also negatively affect the diversity and growth of plants, which is particularly significant for the management of weeds. Last but not least, AMF play a critical role in soil aggregation, thanks to their thick extraradical hyphal network, which envelops and keeps the soil particles compact. It has been  suggested that glycoproteins (glomalin and glomalin related proteins) secreted by AMF into the soil could exert a key role in this process . These proteins are exuded in great quantities into the soil, and could have implications on carbon  sequestration. This potential capability of AMF is likely to contribute to a great extent to the soil ecosystem carbon dioxide (CO2) sequestrationprocess. This aspect has led to the recognition of the importance of this group of organisms in processes related to climate change mitigation.

Nice response Abhishek...

Provision of contrasting ecosystem services by soil communities from different agricultural field ( Plant Soil DOI 10.1007/s11104-011-0828-5)

Several studies have shown that soil biotic communities from organically managed fields are more diverse and exhibit higher activity levels compared to conventionally managed fields. The impact of these different soil communities on plant productivity and the provision of soil ecosystem services are, however, still unclear. Here, we test the effects of soil inoculation from each of three organic and three conventional maize fields on maize productivity and nutrient loss during leaching eventsinduced by simulated rain. In particular, we examine whether differences in productivity and nutrient loss are related to the abundance and species composition of arbuscular mycorrhizal (AM) fungi. We hypothesized that soil biota from organically managed fields would improve maize growth and reduce nutrient leaching significantly more than those from conventionally managed fields. In contrast to our hypothesis, we found that plant productivity was negatively affected by soil inoculation, and this effect was stronger with inoculum from organic fields.

Plant productivity was inversely correlated with AMF abundance, suggesting that enhanced carbon allocation to AMF is at least in part responsible for plant growth reduction under our experimental conditions. However, soil inoculation did alter the ecological functioning of the system by reducing phosphorus leaching losses after simulated rain. Moreover, these leaching losses were lower with increased hyphal density and were related with abundance of particular AMF types, suggesting that abundance of AMF and their community composition may be useful indicators of phosphorus leaching losses. The results demonstrate that soil communities from different agricultural fields vary in their impact on plant productivity and nutrient leaching losses. The results further indicate that there is a potential tradeoff between positive effects of soil communities on sustainability and negative effects on crop productivity. PDF enclosed for further reading...

Whether any attempt has been made to decode the communication signals between host plant and AMs?

interesting question Dr Deka , appreciate you . 

Understanding the behavior of mycorrhiza-originated glomalin, either of plant or soil origin, is anticipated to facilitate better opportunities of modulating antioxidants and carbon distribution in plants. In this study, trifoliate orange seedlings with half of roots were colonized by Acaulospora scrobiculata and Funneliformis mosseae in a split-root rootbox. Mycorrhizal inoculation showed a significantly higher plant biomass of trifoliate orange, regardless of mycorrhizal species. Glomalin-related root protein showed a systematic increase in non-mycorrhiza-inoculated chamber under inoculation with A. scrobiculata and F. mosseae than under non-mycorrhizal inoculation. Similar increase was also observed in easily extractable glomalin-related soil protein and total glomalin-related soil protein as a result of F. mosseae colonization only. Mean weight diameter and soil organic carbon were significantly higher under mycorrhization than non-mycorrhization, irrespective of mycorrhized or non-mycorrhized chamber. Mycorrhizal inoculation stimulated an increase in soil protease activity in the mycorrhized chamber, without any distinctive change in the non-mycorrhized chamber. These results, hence, suggested that mycorrhization conferred a systematic increase in glomalin synthesis in roots and soils, collectively, aiding in better aggregate stability and soil carbon sequestration. PDF enclosed for further reading ..

So exciting to seee such works of real class. thanks Abhishek for taking so much of pain to unearth the relevant literature for all of us. 

I am enclosing very good piece of work , how AMs communicate with host palnt  through typical sod culture . Here is the abstract :  

Sod culture with white clover is a common practice as part of soil management in citrus orchards. However, it is not clear whether such sod culture affects plant growth, soil properties, and the mycorrhizosphere of citrus. In this study, white clover was planted around trifoliate orange (a popular citrus rootstock) under mycorrhization with or without Rhizoglomus intraradices. After four months, the

sod culture substantially stimulated root mycorrhizal colonization and soil hyphal growth. Plant growth performance of trifoliate orange was significantly increased by either mycorrhization under non-sod culture or sod culture under non-mycorrhization, whereas sod culture under mycorrhization significantly decreased the growth performance. Both mycorrhization and sod culture significantly increased the concentrations of easily extractable glomalin-related soil proteins (EE-GRSP), total GRSP (T- GRSP), and soil organic carbon (SOC), the distribution of water-stable aggregates in the size of 2–4, 1–2, and 0.5–1 mm, and the activity of soil peroxidase and phosphatase. The mean weight diameter was notably increased by mycorrhization, irrespective of sod or non-sod culture, but was higher with sod culture under mycorrhization than under non-mycorrhization. Root colonization, soil hyphal length, SOC, EE-GRSP, and T-GRSP were significantly and positively correlated with aggregate stability. These results suggested that sod culture stimulated mycorrhizal development and potentially improved soil properties in an AMF-inoculated citrus orchard.

PDFenclosed for further reading....

Hats off to you , Abhshek for your  precise  ability to address such issues with so much of accuracy , and so informative indeed .

The recent discovery that AM fungi secrete symbiotic signals that resemble rhizobial lipochito-oligosaccharides (Maillet et al. 2011) brings the similarities between these two symbioses even further.

I invite further discussion on this very important issue....

Some soil microorganisms like arbuscular mycorhizal fungi (AMF) inhabit the rhizosphere and develop a symbiotic relationship with the roots of most plant species. AMF can significantly improve resistance of host plants to varied biotic and abiotic

stresses.

Article Arbuscular Mycorrhizal Symbiosis and Abiotic Stress in Plant...

Very true, AMF can significantly improve resistance of host plants to varied biotic and abiotic stresses, but how best we can adopt in commercial system successfully.

Thanks Dr Malhotra and Abhishek , this  is one glaring gray area about AM-research. we absolutely do not bother about the mass multiplication protocols for different species of AMs.  And , such protocols need to be further domesticated at farm level to popularise the large scale use of AMs to harness better  crop response and engineer different crops to fight out a variety of biotic as well as abiotic stresses..?

I feel time is not so long that we can sell out AMFs formulations in market.

Dear Sikha Deka,

Check out the Mycorrhiza Applications Dr. Mike Amaranthus is the CEO and he does a wonderful job explaining his commercial mycorrhizal inoculum. 

This will be a good information for your interest in commercial market.

Best Regards, PRH

Paul , and other colleagues , do you feel AMs have some synergistic effects on the proliferation of other soil microbial communities..?

Yes Anoop the AM activity is definitely associated with soil microbial proliferation and here is the mechanism. The role of photosynthesis for our plant community is to produce biomass from primary production. We need to understand most our nutrition under our feet depends on the air and our soil condition.The plant Carbon based products are the material which leads to the ability of mycorrhizal fungi to be supported or fed.. The amount of Carbohydrate going to the mycorrhizal component and the associated microbial communities is estimated at being one fifth to a quarter of all the primary productivity. As Doctor Amaranthus explained that one third of soil Carbon might be related to the glomalin fraction which is an accumulating and refractory material. As soils increase in soil organic matter the levels of soil microbial activity numbers and diversity are supported. Because we as heterotrophs we are limited by our nutrition. The optimization of the plant and associated communities are all a part of the mutual feeding arrangement. The ability of symbiotic arrangements to increase this is fundamental to a virtuous cycle of the plant productivity being able to increase symbiosis which will lead to improved soil condition giving productivity and soil regeneration. An example of this advance of improved soil conditions is found in the employing of legumes which can in turn increase the earthworm activity and improve the soil organic matter level and physical structure. In the case of termites the gut of the animal has capacity to have high rates of biological Nitrogen fixation and recent studies in Australia show that when the termites are removed the soil Nitrogen levels crashed. The symbiotic relationships are the keys to improving the soil environment without the necessity to be hooked on synthetic chemical inputs which can undermine the natural fertility cycle. Our soil organic matter serves as bank account and the monitoring of its level is essential to improving our results over the long term. 

I think glomalin deposited ERM of AMs help in supplying synergistic effects on other microbial communities.

Abhisek, there  is every possibility AMs will respond favorably with higher co2 due to fertilizing ability of roots. I agree with response of Dr Paul.

 Interesting to know that elevated CO2 stimulates mycorrhizal colonization. New evidence suggests that the observed CO2 effects on arbuscular mycorrhizal fungi are indirect and are a result of faster plant growth at higher CO2 concentrations. The reasons are First, elevated [CO2] leads to greater carbohydrate availability in the root system, which should be of benefit to the fungus and hence to the host plant, because the mycorrhiza will have an increased capacity for nutrient uptake (especially phosphorus). Second, mycorrhizal colonization could increase the capacity of the plant’s response to elevated [CO2] by acting as a sink for excess fixed carbon, which might otherwise cause down regulation  of photosynthesis.

Infact , now the impact of AMs is seen through solubilisation , chelation and complexation  of relatively immobile nutrients like Fe, Mn, Zn , besides phosphorous .  you will find plenty of literature on this issue.. And , therefore , AM-inoculation is considered is more comprehensive in impact than any other microbial community in terms of plant overall metabolic changes..

AM inoculation  changes the biological environment of the soil and most of the nutrients are mobilised due to acidifying effect of ERM produced by AM's. 

Dr Shirgure , you are very much right . Can you believe AMs ERM  hyphae can be 60m long in 1g soil , depending upon the species of AM and its dependence on crop . I , therefore , strongly feel, AMs are the strongest soil microbial community  to influence the proliferation of other soil microbial community to bring overall far superior changes in biological activity of rhizosphere of a plant 

Thats a good response Abhishek , how do you feel, can we define carrying capacity of a crop rhizosphere based on AMs diversity..? How much difference does it make in defining the carrying capacity of soil , abundant or poor in AMs diversity..?

I think AM have much greater impact on soil fertility than any other soil microbial community because of ERM frolifarations. 

AMs are supposed to have extended soil ecosystem service dimensions despite bacterial population outweigh AMs population.

I agree with you Dr. Anoop, VAMs are important microbial community  in soil which influence the proliferation of other microflora in rhizospher which significantly contribute for superior changes in biological activity of rhizosphere of a plant .

Biological properties  of the soil are more governed by bacterial population, many reports have established this fact. 

Dr Deka , here is an excellent article entitled Rhizobacteria elevate principal basmati aroma compound accumulation in rice variety by Deshmukh et al published in rhizosphere . The abstract is reproduced here : 

The rhizobacteria from soils cultivated with basmati(BM) and non- basmati(NBM) rice for  long duration were isolated and screened for t he production of principal basmati aroma compound2-acetyl-1-pyr- roline (2AP). Isolates of BMoriginhad significantly higher frequency of 2AP production as compared to non-basmati control.These isolates also differed in the irvolatile profiling. Strainsof Acinetobacter sp. from Morigin had greater potential of 2AP production as compared to other rhizobacterial isolates.Five bacterial   strains(strainsof Acinetobacter sp and Enterobacter ludwugi),  with different 2AP production capacity wereselectedforrootsysteminoculationofBasmati- 70plant. 2AP levels of basmati grains werequantified  by gas  chromatography.The inoculated plants exhibited 1.14-1.41foldincreasein2AP levels. The inoculation effect was more pronounced with the high2AP producing isolates.The overall results suggest that further dose and optimization of inoculation methodology will be needed to extend this academic experiment to commercial levels.PDF enclosed for further reading...

friends , is it possible to rehabilitate the  soils polluted  with heavy metals  using different strains of AMF....If so, how does it affect the population load of other soil microbial communities..?

obviously ....!, not only because they behave always beneficial for plants, they advance nutrient absorbance (without them nutrient absorbance is seriously questioned), but they also influence the resistance of plants under multiple stress conditions

It is really very challenging, once we think for multiple stress tolerance. This can be achieved through an integrated approach utilizing resistant/tolerant genes, better crop management and utilizing power of soil-plant-microbial trio for improving crop resistance. 

Let me raise a common issue.  Where do accumulated phosphorous by AMs divert in which part of AMs. Is it only vesicles and arbuscules?

Very interesting Dr Deka. Probably , this kind of responses from we are getting through some other question as well , where total phosphorous of the soil is observing an increase after AMF inoculation , question is , where such increase in phosphorous  is coming from..?

The uptake and accumulation of phosphorus by mycorrhizal and nonmycorrhizal onion plants were compared. The results of the experiments indicate:1.Mycorrhizal onion plants accumulated significantly more phosphorus in the roots and tops than nonmycorrhizal plants. 2.Vesicular-arbuscular mycorrhizae are sites of increased phosphorus accumulation compared to nonmycorrhizal roots. 3.A fungitoxicant (parachloronitrobenzene) reduced phosphate accumulation by mycorrhizae but did not significantly affect phosphate accumulation by nonmycorrhizal roots.

http://link.springer.com/article/10.1007/BF01881967

An excellent work on endophyte consortium...

Thanks Dr Malhotra fro providing nice link and putting the discussion further on a interesting note : 

With increasing effects of global climate change,there is a strong  interest in developing biofuels from trees such as poplar (Populus sp.)that have high C sequestration rates and relatively low chemical inputs. Using plant-microbe symbiosis to maximize plant growth and increase host stress tolerance may play an important role in improving the economic viability and environmental sustainability of poplar as a feedstock. Based on our previous research, a total of ten endophyte strains were selected as a consortium to investigate the effects of inoculation on commercial hardwood cuttings of Populus deltoides × P. nigra clone OP-367. After one and a half months of growth under non-stress conditions followed by one month under water stress, there was substantial growth promotion with improved leaf physiology of poplar plants in response to the endophyte inoculation. Furthermore, inoculated plants demonstrated reduced damage by reactive oxygen species (ROS) indicating a possible mechanism for symbiosis-mediated drought tolerance. Production of important phytohormones by these endophytes and identification of microbial genes involved in conferring droughttolerance suggests their potential roles in the modulation of the plant host  stress response. Source ; Current Plant Biology 6 (2016) 38–47