Arbuscular mycorrhizal fungi prevent mercury toxicity in Lactuca sativa (L.) seed germination

Mercury pollution is an issue of global concern. In Colombia, the use of contaminated water for food crop irrigation and artisanal mining contribute to mercury pollution in soil, affecting food production and restoration of perturbed areas. Mycorrhizal fungi are plant symbionts that provide benefits to plants, including resistance to heavy metals, but fungal effects on germination remain to be fully described. In this study, it was tested the effect of mercury and mycorrhizal fungi onLactuca sativaseed germination. A 2x5 completely randomized factorial experiment was performed to assess the effect of five HgCl2polluted treatments, two mycorrhizal treatments (i.e., with inoculum, without inoculum), and the interaction of both factors on seed germination, seedling root colonization, pH, and final water content. Without mercury, mycorrhizal fungi had an inhibitory effect on seed germination. Testing the effect of mercury on seed germination showed a significantly inhibitory effect of mercury on germination. However, in pots inoculated with arbuscular mycorrhizal fungi showed constant germination probabilities, independently of mercury concentration. According to the best model determined for the data, a key step in the mitigation of mercury toxicity in seed germination is to prevent substrate pH changes. The environmental conditions of the experiment contributed to activating a densely populated biomass of inoculum, promoting root invasion from various points. Overall, the presence of mycorrhizal fungi in seedbeds could lead to a reduced number of plant individuals. However, the use of a fungal inoculum in polluted environments highly contributes to plant stablishment.