Diagnose of Indigenous Arbuscular Mycorrhizal Communities Associated to Cynara cardunculus L. var. altilis and var. sylvestris.

Cynara cardunculus L. is a perennial species with high potential for bioenergy production. Arbuscular mycorrhizal symbiosis (AMF) is probably the terrestrial symbiosis most extended on earth. It presence in roots and soils improves plant nutrition and soil quality. Indigenous AMF have developed a variety of modifications to survive in their habitat and thus could serve as potential inoculants for the implantation of plant species in the respective AMF soil habitat. This work aimed to diagnose the status of the AMF symbiosis associated to two cardoon cultivars after a year of growth in a saline soil and in a conventional farming soil. For that purpose we determined AMF parameters in 4 rhizospheric soils and in roots of the cardoon varieties. We found that: (1) the rhizosphere of C. cardunculus var. altilis positively influenced the extraradical mycelium development in the saline soil, (2) the inorganic fertilization history of the conventional farming soil could have had a negative effect on the AMF community and, (3) the intraradical mycelium (IRM) development was extremely low. Our diagnosis suggests that, in order to improve the positive effects of AMF on cardoon growth and soil quality, efforts should be focused on the development of the IRM. In a boarder sense, the implementation of a diagnosis of indigenous AMF communities as a general agronomic practice could become an useful tool to farmers that are willing to potentiate the benefits of AMF on plant growth and soil quality.

Short-term chromium (VI) exposure increases phosphorus uptake by the extraradical mycelium of the arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 41833.

Hexavalent chromium is a potent carcinogen, while phosphorus is an essential nutrient. The role of arbuscular mycorrhizal fungi (AMF) in the uptake of P is well known and was also reported, at low levels, for Cr. However, it is unclear whether the uptake of Cr can impact the short-term uptake dynamics of P since both elements have a similar chemical structure and may thus potentially compete with each other during the uptake process. This study investigated the impact of Cr(VI) on short-term P uptake by the AMF Rhizophagus irregularis MUCL 41833 in Medicago truncatula. Bi-compartmented Petri plates were used to spatially separate a root compartment (RC) from a hyphal compartment (HC) using a whole plant in vitro culture system. The HC was supplemented with Cr(VI). Chromium(VI) as well as total Cr and P were monitored during 16 h within the HC and their concentrations determined by the end of the experiment within roots and shoots. Our results indicated that the uptake and translocation of Cr from hyphae to roots was a fast process: roots in which the extraradical mycelium (ERM) was exposed to Cr(VI) accumulated more Cr than roots of which the ERM was not exposed to Cr(VI) or was dead. Our results further confirmed that dead ERM immobilized more Cr than alive ERM. Finally our results demonstrated that the short exposure to Cr(VI) was sufficient to stimulate P uptake by the ERM and that the stimulation process began within the first 4 h of exposure.