Plants need to discriminate against toxic levels of salt ions, and simultaneously build up a strong water potential in their roots to overcome the physiological drought associated with salinity. Ion selection can take place at different membranes when entering root cells or at xylem loading. Arbuscular mycorrhizal fungi (AMF), which are symbiotically associated with most plants on earth, can be found under severe salinity and are known to improve plant growth even under salt stress conditions. To consider AMF as an ion filter for plants is a new thought. To elucidate this, we analyze the elemental composition of AMF grown in different salinity conditions.
Furthermore, we investigate the influence of salinity in situ on AMF and treatments to improve AMF growth in the pre-saharan semi desert in Tunisia. Different organic and inorganic amendments are tested, and an attempt of Acacia afforestation with the help of inoculation of both AMF and Rhizobium is evaluated.
Results/Conclusions Our, many of them very preliminary, results: The proton induced x-ray emission (PIXE) studies on AMF field material showed discrimination against Na ions, but a strong accumulation of Cl, suggesting a possible pre-selection of ions before delivery to the plant. When G. intraradices in axenic cultures was exposed to salinity gradients on the other hand, it also showed Na discrimination, but it did show no strong Cl enrichment but K accumulation, the same when only osmotically stressed with Glycerol.
In a natural salt gradient, the amount of extraradical mycelium decrease with rising salinity, but spore number in the soil seems to increase. The amendment experiment showed that treatments improving general soil properties as different kinds of organic matter, especially if high in P, increased AMF biomass, while inorganic treatments as P addition did not. Inoculation with a commercial AMF and rhizobium strain did not affect plant growth and survival significantly after 5 years.
