At present, drought and soil salinity are among the most severe environmental stresses that affect the growth of plants through marked reduction of water uptake which lowers water potential, leading to osmotic stress. In general, osmotic stress causes a series of morphological, physiological, biochemical, and molecular changes that affect plant performance. Several studies have found that diverse types of soil microorganisms improve plant growth, especially when plants are under stressful conditions. Most important are the arbuscular mycorrhizal fungi (AMF) which form arbuscular mycorrhizas (AM) with approximately 80% of plant species and are present in almost all terrestrial ecosystems. Beyond the well-known role of AM in improving plant nutrient uptake, the contributions of AM to plants coping with osmotic stress merit analysis. With this review, we describe the principal direct and indirect mechanisms by which AM modify plant responses to osmotic stress, highlighting the role of AM in photosynthetic activity, water use efficiency, osmoprotectant production, antioxidant activities, and gene expression. We also discuss the potential for using AMF to improve plant performance under osmotic stress conditions and the lines of research needed to optimize AM use in plant production.

Soil salinity is the biggest problem which hinders the productivity of agricultural crops, causing adverse effects on plant growth and development. In this regard, it has been shown that the arbuscular mycorrhizal fungi (AMF) can establish a symbiosis with most agricultural plants improving water and nutrient absorption under salinity stress conditions. The functional contribution of AMF strains (Claroideoglomus claroideum (Cc) and a native consortium of AMF (HM) isolated from saline soils) on the growth and nutrition of lettuce plants (Lactuca sativa var. longifolia) was evaluated under increasing salt stress conditions (0, 40, and 80 mM NaCl). At 60 days of growth, biomass production, nutrient content (N, P), ions (Ca 2+ , Mg 2+ , Na + , K +), chlorophyll, proline content, and AMF propagules were evaluated. The highest growth was observed in plants inoculated with Cc, which produced a higher percentage of root colonization and hyphal length at all levels of salinity, compared to plants inoculated with HM or non-inoculated plants. These results were directly related to higher biomass production, increased synthesis of proline, increased N uptake, and noticeable changes in ionic relations, based in a diminishing Na + , compared to non-mycorrhizal plants. Our results suggest that this improved ionic balance is due to a filtering effect of AMF structures both in the soil and in the root that prevents the entry of toxic Na + ions, which is important due to the level of lettuce production on saline soils improving the crop by means of directed inoculation with efficient AMF strains.

A constructed wetland (CW) in arid areas requires special knowledge given the particular climatic conditions. Among other aspects, the Hydraulic Retention Time (HRT) and plant species may be two important design parameters in hyper- and super-arid areas. Therefore, the study aimed to evaluate the influence of both variables in the application of CW in super-arid areas. Two HRT, 3.5 d and 7 d, and plant species classified by their origin: (a) native, Festuca Orthopylla, Cortaderia atacamensis and Schoenoplectus americanus, and (b) foreign, Cyperus papyrus, were evaluated in four Mesocosm Constructed Wetlands (MCW) operated in a super-arid area. The results showed that the HRT significantly increased (α < 0.05) in more than 10% the removal efficiency of nitrogen and phosphorus forms (TN, NH-N, TP, PO-P). These results were the same for the two groups of plants assessed. Moreover, Cyperus papyrus significantly increased (α < 0.05) above 30% the removal efficiency, but only for nitrogen and phosphorus forms. MCW with this plant species showed a water loss above 25% and significantly increased (α < 0.05) the Electrical Conductivity (EC) of effluents. MCW planted with Schoenoplectus americanus showed water losses of around 25% for the both HRT evaluated, and its influence was not significant (α > 0.05) on the EC of the effluents. These results suggest that Schoenoplectus americanus would be an ideal candidate species for use in CW with subsurface flow in super-arid areas, with HRT varying between 3.5 d and 7 d.

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