Abstract

Arbuscular mycorrhizal (AM) fungi are soil borne fungi forming symbiotic relationship with majority of higher plants providing a direct link between soil and plant roots. AM fungi undergo a multi-step colonization process before benefiting the host plant. The strong glue glomalin is a glyco protein produced by an AM fungi. The deposition of glomalin on soil particles leads to buildup and stabilization of aggregates, which leads to better soil structure which in turn leads to increased soil water availability under water stress condition. The mycorrhizal colonization is effective aggregators and therefore management of mycorrhizal fungi can be considered as a biological amendment for soil structure and other soil physical properties. Mycorrhizal plants could take up more metal nutrients via extraradical hyphae, which provide larger surface areas than the roots alone and reduce the distance for diffusion, thereby enhancing the absorption of immobile metal nutrients (especially Phosphorus and Zinc). Mycorrhizal inoculated plants produce larger biomass as a direct consequence of improved photosynthetic activities and translocate 20 to 30% of the assimilated C to the underground where mycorrhizal structures conserve soil carbon. AM symbiosis enhanced the plant growth by increasing plant access to immobile mineral ions mainly Phosphorus and Zinc, improving physical conditions and by binding heavy metals into roots that restricts their translocation into shoot tissues. The mycorrhizal symbiosis assists in biofortification of micronutrients such as Fe and Zn in maize grain irrespective of calcareous and non-calcareous soils. The mechanism involved in improved micro nutrition of maize includes acidification of rhizosphere; siderophore production enhanced physiologically active Fe and production of anti-oxidants besides synergistic interaction between P and micronutrients.

Key words: Mycorrhiza, soil aggregation, micronutrients, carbon sequestration, heavy metals, enzymatic activity, glomalin, biofortification.