Daniela Tsikou

Arbuscular mycorrhizal fungi (AMF) are plant symbionts that have a pivotal role in maintaining soil fertility and nutrient cycling. However, these microsymbionts may be exposed to organic pollutants like pesticides or veterinary drugs known to occur in agricultural soils. Anthelminthics are veterinary drugs that reach soils through the application of contaminated manures in agricultural settings. Their presence might threaten the function of AMF, considered as sensitive indicators of the toxicity of agrochemicals to the soil microbiota. We determined the impact of the anthelminthic compounds albendazole and ivermectin on the establishment and functionality of the symbiosis between the model-legume Lotus japonicus and the AMF Rhizophagus irregularis. Our analyses revealed negative effects of albendazole on the development and functionality of arbuscules, the symbiotic organelle of AMF, at a concentration of 0.75 μg g−1. The impairment of the symbiotic function was verified by the reduced expression of genes SbtM1, PT4 and AMT2;2 involved in arbuscules formation, P and N uptake, and the lower phosphorus shoot content detected in the albendazole-treated plants. Our results provide first evidence for the toxicity of albendazole on the colonization capacity and function of R. irregularis at concentrations that may occur in agricultural soils systematically amended with drug-containing manures.

Aims This study aims to identify main factors that influence the tripartite association of legumes with arbuscular mycorrhiza fungi (AMF) and nitrogen-fixing rhizobia. Methods and Results Concurrent inoculations with Mesorhizobium loti and four AMF strains were performed on the model legume Lotus japonicus. Nodulation was significantly enhanced by all AMF strains, under normal conditions, and by specific AMF strains under heat-stress conditions. The impact of rhizobia on mycorrhizal colonization was AMF strain dependent. Co-inoculation trials, where either AMF or rhizobia were restricted outside the root, showed that the symbiotic phenotypes are not influenced by microbial interactions at the pre-symbiotic stage. External application of nutrients showed that P enhances nodulation, while N application does not enhance mycorrhizal colonization. Conclusions Nodulation and mycorhization affect one another during advanced stages of the symbiosis. AMF strains may enhance nodulation under both normal and high environmental temperatures. Rhizobium-AMF compatibility is critical, as rhizobium may positively affect specific AMF strains, an effect that does not derive from increased N uptake.