Could the fluoride-tolerant species Panicum maximum replace sensitive plants in fluoride biomonitoring?

Fluoride (F) is the most phytotoxic atmospheric pollutant. The use of plants for passive or active biomonitoring has been a common strategy to detect abnormal atmospheric F concentrations. Tree species are mostly used, although the high sensitivities of some, associated with costly processes of plant replacement, will increase cost outlays associated with F-biomonitoring processes. After a few days of exposure, F-sensitive species often die, and must be replaced in active biomonitoring stations. We therefore investigated the potential use of the grass Panicum maximum for atmospheric F biomonitoring. Although that grass shows fast accumulations of F in their leaves, no visual symptoms of intoxication were observed. Despite of their F-tolerance, plants showed reliable microscopic responses to F (epicuticular wax erosion, plasmolysis of bulliform cells, and damage associated with trichomes). Since microscopic evaluations are mandatory in F-biomonitoring projects, the use of grass species such as P. maximum that show F-tolerance, fast F-uptake and reliable microscopic responses, could represent an option for F biomonitoring that would decrease costs related to plant production and replacement in monitoring stations.