Very good question. Surely the answer is in between.AMs have a huge role in improving plants ability both physiologically and biochemically through a series of enzymes to not only plant nutrition but add another dimension of antioxidants profile to offer much better resistance to plants under water stress or any other kind of stress including salt stress...

Very good question. Surely the answer is in between.AMs have a huge role in improving plants ability both physiologically and biochemically through a series of enzymes to not only plant nutrition but add another dimension of antioxidants profile to offer much better resistance to plants under water stress or any other kind of stress including salt stress...

A nutrient depletion zone can develop when there is rapid soil solution uptake, low nutrient concentration, low diffusion rate, or low soil moisture. These conditions are very common; therefore, most plants rely on fungi to facilitate the uptake of minerals from the soil. Mycorrhizae, known as root fungi, form symbiotic associations with plant roots. In these associations, the fungi are actually integrated into the physical structure of the root. The fungi colonize the living root tissue during active plant growth.

Through mycorrhization, the plant obtains phosphate and other minerals, such as zinc and copper, from the soil. The fungus obtains nutrients, such as sugars, from the plant root. Mycorrhizae help increase the surface area of the plant root system because hyphae, which are narrow, can spread beyond the nutrient depletion zone. Hyphae are long extensions of the fungus, which can grow into small soil pores that allow access to phosphorus otherwise unavailable to the plant. The beneficial effect on the plant is best observed in poor soils. The benefit to fungi is that they can obtain up to 20 percent of the total carbon accessed by plants. Mycorrhizae function as a physical barrier to pathogens. They also provides an induction of generalized host defense mechanisms, which sometimes involves the production of antibiotic compounds by the fungi. Fungi have also been found to have a protective role for plants rooted in soils with high metal concentrations, such as acidic and contaminated soils.These papers shall give you insite.

you asked three questions i would try to answer one by one. First of all everything created by nature is useful and have its own role, which is may not be exploited yet. Yes symbiosis have a role in improvement of plant production e.g. 80% of plants exchange mutual benefits with AMs.

Symbionts are natural biofertilizers, provide plants water, nutrients, and protection, in exchange for photosynthetic products. Thus, when missing or impoverished, can lead to a less efficient ecosystem functioning.

overall, it is a positive relation but for stable use of symbiosis in agriculture is to carry out multi-location field trials and conduct cost-benefit analyses, to increase awareness among farmers.

indigenous symbionts performed better than commercial or culture collection isolates, farmers should be encouraged to produce their inocula, from native soils. This makes things more affordable for farmers,especially for developing countries, where sustainability in crop production is essential now, more than ever.

The fungi are not only important in the promotion of nutrient uptake but often also reduce the susceptibility of the plant to phytopathogenic fungi and nematodes. Below paper will give you detailed answer to your question:

Miller RM, Miller SP, Jastrow JD, Rivetta CB (2002) Mycorrhizal medicated feedbacks influence net carbon gain and nutrient uptake in Andropogon gerardii. New Phytol 155:149–162

See example of Sesbania rostrata.

symbiosis plays an important role in plant growth especially in legumes the symbiotic partner forms nodules with the native rhizobia as well as with the inoculated ones. in the soils in which rhizobia had been inoculted earlier, response is not so significant as inoculated ones have to compete with the native rhizobia. Some endophytes like Acetobacter diazotrophicus fixes nitrogen upto 150 kg in sugarcane.

AM fungi secretes auxins, make available phosphorus to the plants and provide moisture to the plant under drought conditions. When AM fungi are coinoculated with rhizobia, this effect is enhanced.

PLANT NUTRITION.

The symbiotic process between legumes and compatible soil rhizobia is key to their survival in low nitrogen (N) environments. Some symbiotic grain legumes growing in the field could obatain in excess of 80% N requirements from symbiosis leading to enhance plant growth and grain yield. It is in this regard that legumes are sometimes iniculated with superior rhzobial strains for increased productivity. However, inoculation failures are sometimes encountered in the field due the high competitive ability of resident/indigenous rhizibial strains. Nevertheless, a notable example of inoculation success is that of Soybean in Brazil, which is estimated to save the country about US$10 billion in a cropping season; thanks to symbiotic nitrogen fixation.

While geared towards gardeners, a good general overview can be had from

Teaming with Microbes: A Gardener's Guide to the Soil Food Web by Jeff Lowenfels and Wayne Lewis. Lowenfels has also written Teaming with Fungi along the same lines.

Paul Stamets is also an authority on fungi, and has a fascinating book Mycelium Running: how mushrooms can help save the world. Another broader treatment of the topic is Radical Mycology by Peter McCoy.

There are likely an abundance of technical applications once we appreciate the diversity and complexity of what is occurring largely out of our field of view, but critically vital to ecological systems.