Abstract
Mycorrhizas are known to improve host plant nutritional status as a consequence of water transport from the soil to the host plant through the external mycelium as a direct effect or improved host plant nutrition primarily, phosphorus as an indirect effect. The direct hyphal water transport is quantified to be meager and a major part of the benefits of mycorrhizal symbiosis is indirect and nutritionally related. In arid and semi-arid regions where drought occurrence is very frequent and soil moisture content is highly restricted, mycorrhizas can assist in exploiting the soil beyond the rhizosphere that helps the host plant to withstand drought stress conditions. The drought tolerance in mycorrhiza-inoculated plants is quite complex and such response is due to a series of processes such as improved nitrogen (N) availability in soils, extensive root surface area and cationic exchange capacity, collective N assimilatory pathways in plant-mycorrhizal system, luxuriant uptake of nutrients besides remobilization of nutrients to support grain growth. These physiological, biochemical, nutritional and morphological changes in the mycorrhizas associated host plants have contributed to the ability of the host plants to survive under limited water environments. Despite mycorrhiza-assisted and N nutritionally enabled host plant drought tolerance is evident, more research is required to gain insights into the mechanisms involved. This review highlights the role of mycorrhizas on N dynamics in the rhizosphere and enhanced host plant N nutrition that collectively contributes to the sustained crop productivity under drought stress conditions.
Highlights
Drought stress in arid and semi-arid regions is quite common where the abiotic stress limits plant growth and reduces crop production across the globe
Despite the fact that the literature review clearly demonstrates that the role of mycorrhizal symbiosis in increasing the availability of N in soils is very trivial, the contribution may be significant in the context of drought conditions where nitrogen availability is very crucial for crop growth and sustaining farm productivity
2012 elucidated the mechanisms involved in biogeocycling of nutrients by differentially altering the C supply to the host and subsequent changes in uptake and transfer of N in arbuscular mycorrhizal fungal (AMF) They found that the C supply from the host plant invokes biochemical changes that mediate uptake and transport of N in the symbiosis a phenomenon that is governed by respective changes in fungal gene expression especially in adequate C availability
Summary
Drought stress in arid and semi-arid regions is quite common where the abiotic stress limits plant growth and reduces crop production across the globe. Nitrogen-fixing bacteria and arbuscular mycorrhizal fungi (AMF) are of global significance in inducing drought tolerance in host plants(Subramanian and Charest, 1995; 1997; Augé, 2001; Barea et al, 2005; Hidri et al, 2016).
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