Dear,

I feel that, you are not efficiently expressing, what the problem actually is. Therefore, I suggest you to kindly modify the writing after getting help from any local colleague.

Regards.

Thank you very much

Selim Nouara

I would rather say if it's possible that the  plant can stop his transfer carbon to the fungus, and if it's possible, what are the causes of that?

When Phosphorus levels are high the host citrus many not produce compounds which are secreted into the root zone and are attractant giving stimulation of mycorrhizal fungi to grow toward and then in the root.

With this in mind the plants used as hosts are often amended with nutrient solution low in Phosphorus. In the low Phosphorus state the flavonoids produced by the plant are the initiators of the mutual relationship.

Grasses, legumes composites and alliums are very good hosts of a variety of mycorrhizal fungi. Using natural soil from a permanent prairie or pasture would host a variety of mycorhizae. If you use a 40 40 20 mixture of vermiculite, perlite and prairie or pasture soil grow the grass, legume, composite and allium mix in grow pots of bags and test the soil mycorrhizae sporania in the soil after a growth cycle.

After the growth cycle and enumeration of spore number make a soil to mixture dilution to give 200 sporangia per pot. Your pots will be used to grow root stocks. This will insure that the root stocks will by mycorrhizal colonized.

Studies suggest some advantages to the use of diverse mycorrhizal mixes compared to single species inoculations. 

Dear,

Thanks for writing again. What I learn from your question is that, you want to ask whether, plant can stop C transfer to the fungus.

First of all we should keep in mind, that the mycorrhizal associations are symbiotic, which means bidirectional transfer. Second, being a fungi (heterotrophs), mycorrhizal partner can never synthesis C for their own, and plant can not absorb P from soil, because of unavailable form (compounds of Al, Ca, Fe, and other organic forms).

So, what is critical for  this association is the bidirectional need and hence transfer. Thus, plant can not stop transferring C to the fungus, because it will shift/break the symbiosis.

Regards.

Dear,

thank you for you response.

So the plant host will never stop the exchange, but it's possible that the fungi doesn't give many nutrient, and  commensalism  begin?

 Yes the fungus has no ability to synthesize Carbon energy as Carbohydrate sugar it is totally dependent on the Plant source for these. It is not capable of growing on its own as a saprophyte on dead material and needs a live plant host.

The plant can grow on its own without the fungus.  The deficiency of Phosphate from the soil will stimulate the plant to produce strigolactones which when exudated into the soil stimulate growth of the mycorrhizal fungus to the root system. This association will be maximized in deficient soil Phosphate environments.

The plant status can then serve as a turn on for mycorrhizal fungus since strigolactones are produced in response to P deficiency. The plant can get Phosphorus from mycorrhizal fungi but also from the soil solution.

The strigalactones are growth regulators for the mycorrhizal fungus and for the plant itself. Smith in Australia has a very good summary of the information of how strigalactones function. The nutrient flow is C to fungus and P to plant but mycorrhizal fungus provides a conduit for water, Zinc, Copper and other nutrients. 

Yes , well said  Paul...An excellent review chapter by Ibrahim Ortas..AMFs are now equally efficient towards other nutrients like Fe, Mn, Zn etc to  a variety of host plants including citrus...

In this review, effect of mycorrhizal inoculation on citrus growth, nutrient and water uptake, and mycorrhizal dependency was searched. Arbuscular mycorrhiza (AM) is symbiotic associations between 90% of higher plants and fungi. Since citrus plants have very few and short root hair, in order to get sufficient nutrient and water, they need mycorrhizal coloni­zation. It has been shown that the host plant was a factor affecting the interaction between mycorrhizal fungi. It has been shown that greater fungal activities in AM hyphae have a significant effect on citrus growth and nutrient uptake.

Mycorrhizal fungi differ in their ability to improve citrus cultivar growth. AM species have different responses to different citrus cultivar’s nutrient uptake, particularly less mobile phosphorus (P), zinc (Zn), and copper (Cu). Under arid and semiarid soil conditions, mycorrhizae enhanced acquisition nutrient to the host plants. AMF also improves water relations under drought-stressed conditions. Effect of different mycorrhizal species under different soil conditions on citrus rootstocks was also evaluated. AMF-colonized citrus seedlings quality is high. Mycorrhizal inoculation also increases plant resistance against stress conditions such as salt, drought, and temperature as well.

Also mycorrhizal hyphae contribute on soil aggregation; by this way, soil fertility can increase. AM fungus colonization had been shown that enhanced plant growth under drought stress indirectly through affecting the soil moisture retention via glomalin’s effect on soil water-stable aggregates development. Studies have shown that mycorrhizal fungal hyphae participate in uptake and transport of water to host plants. Also, the mechanism behind nutrient uptake and water uptake was evaluated in this review. Arbuscular mycorrhizal fungi also increase the activity of soil enzymes, including dehydrogenase, phosphatase, and urease. Soil phosphatase activity was increased with the increase of AM colonization. And these enzymes help plant to be stronger against stress conditions.

Well said Anoop as such the mycorrhizal symbionts are prime biological soil indicators of soil quality in a biological sense. Unfortunately there is a very small community of people with specialized training to apply this important area which has been greatly under studied and reported. The health of mycorrhizal component is also extremely important in Carbon sequestration because the Glomalin glycoprotein secreated by the symbiont is highly resistant to decay stimulating with soil aggregation the accumulation of organic matter in the soil. 

Rightly articulated  response Paul . Deposition of glomalin  into the mycorhizosphere is again a function of  harmony between symbiont and the host plant , which decides the extent of mycorrhizal colonization , and in turn , the addition of  glycoprotein  in form of glomalin ,  as a part of organic matter . This is where AMs have huge potential in offering resilience to the mycorhizosphere as a part of  adoption strategy and enrichment of carbon as an indicator of  reduced GHG emissions, besides agronomic efficiency evident from crop value-cost ratio , a perfect role of AMs in CSA framework....