AMFs and Plant Growth

Agrotica > Crop Management  > AMFs and Plant Growth

The use of beneficial soil microorganisms is a promising strategy for optimizing plant growth and agricultural sustainability. The composition and activity of soil microbial communities largely determine biogeochemical cycles, organic matter renewal processes, and soil fertility and quality. Although microorganisms play a key role in the success of cropping systems through plant nutrition and health, their community composition continues to change with plant developmental stages, especially with soil type and cropping practices. Currently, the evaluation of biological indicators of soil quality is necessary to link the abiotic properties of the soil to changes in its functions in terms of biochemical and biophysical transformations.

One of the most important groups of microorganisms, due to the relevant ecological services they provide in ecosystems, is the arbuscular mycorrhizal fungi (AMF), The word mycorrhiza is derived from the classical Greek word for “mushroom” and “root.” This ancient symbiosis has existed for more than 400 million years. In AM symbiosis, plants allocate a portion of photosynthates to AM fungi to support fungal growth. AM fungi facilitate plant nutrient and water uptake from soil. AM fungi play a critical role in promoting plant growth and enhancing the plant resistance to abiotic and biotic stresses. AM fungi live in symbiosis with most plant species and provide many benefits to host plants, such as improved nutrient uptake—especially of poorly mobile nutrients, such as phosphorus (P)— and increased plant tolerance to biotic and abiotic stressors. Therefore, the productivity and sustainability of agroecosystems can be improved by boosting native AMF while reducing reliance on fertilizers.

Numerous reports describe improved resistance to a variety of stresses including drought, salinity, herbivory, temperature, metals, and diseases due to fungal symbiosis. Nearly 90% of plant species including flowering plants, bryophytes, and ferns can develop interdependent connections with AMF. Formation of hyphal network by the AMF with plant roots significantly enhances the access of roots to a large soil surface area, causing improvement in plant growth. AMF improve plant nutrition by increasing the availability as well as translocation of various nutrients. AMF improve the quality of soil by influencing its structure and texture, and hence plant health.

A majority of the species of AMF belong to the sub-phylum Glomeromycotina, of the phylum Mucoromycota. Approximately 90% of all plants form symbiotic mycorrhizae fungi relationships by forming hyphae networks. Through mycorrhizae the plant obtains mainly phosphate and other minerals, such as zinc and copper, from the soil. The fungus obtains nutrients, such as sugars, from the plant root. In addition, fungi supply inorganic nutrients to plants, such as ammonium, nitrate, and phosphate and they are used as biofertilizers. Rhizosphere microorganisms can overcome competition with other soil factors and survive under variable environmental conditions

AMFs as Bio-Fertilizers

Bio-fertilizers are a mixture of naturally occurring substances that are used to improve soil fertility. These fertilizers are very useful for soil health as well as for plant growth and development.  It is widely believed that AMF could be considered as a replacement of inorganic fertilizers in the near future, because mycorrhizal application can effectively reduce the quantitative use of chemical fertilizer input especially of phosphorus. Continuous use of inorganic fertilizers, herbicides, and fungicides has caused various problems to soil, plants, and human health, through their damaging impact on the quality of food products, soil health, and air and water systems. It is believed that AMF can possibly lower down the use of chemical fertilizers up to 50% for best agricultural production, but this estimate depends on the type of plant species and the prevalent stressful regimes.

AMFs and Mineral Nutrition

AMFs have the capability to boost the uptake of inorganic nutrients in almost all plants, specifically of phosphate. AMF improve the surface absorbing capability of host roots. AMF develop symbiosis with roots to obtain essential nutrients from the host plant and consequently provide mineral nutrients in return, for example, N, P, K, Ca, Zn, and S.

AMFs and Abiotic Stresses

Drought
Drought stress affects plant life in many ways; for example, shortage of water to roots reduces rate of transpiration as well as induces oxidative stress Symbiotic relationship of various plants with AMF may ultimately improve root size and efficiency, leaf area index, and biomass under the instant conditions of drought.

 

Salinity
It is widely known that the soil salinization is an increasing environmental problem posing a severe threat to global food security. Salinity stress is known to suppress growth of plants by affecting the vegetative development and net assimilation rate resulting in reduced yield productivity. Several research studies have reported the efficiency of AMF to impart growth and yield enhancement in plants under salinity stress. AMF significantly alleviated the deleterious effects on photosynthesis under salinity stress.

 

Heavy Metals
AMFs are widely believed to support plant establishment in soils contaminated with heavy metals, because of their potential to strengthen defense system of the AMF mediated plants to promote growth and development. Heavy metals may accumulate in food crops, fruits, vegetables, and soils, causing various health hazards.

AMFs and Diseases

AMF symbioses can enhance plant resistance against various pathogens, including nematodes, fungi, bacteria and viruses, especially soilborne pathogens. Mycorrhizal colonization in root cortex can elicit specific plant reactions and further activate the plant defense system.

Eng. Adnan Mafakheri

Maryse Bou Zeid

mbouzeid@debbaneagri.com

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