Sapindus saponaria bioindicator potential concerning potassium fluoride exposure by simulated rainfall: Anatomical and physiological traits

Fluoride is one of the main phytotoxic pollutants released into the atmosphere. It can be released in the form of potassium fluoride by brick, ceramic, phosphate mineral and aluminum industries, causing damage to different plant species. Sapindus saponaria L. (Sapindaceae) is widely distributed throughout Brazil, and has been used both in the recovery of degraded areas and in urban afforestation. In this context, the aim of the present study was to determine S. saponaria bioindicator potential through morpho-anatomical and physiological responses after simulated rainfall with potassium fluoride. Young S. saponaria individuals, approximately 50 days old, were treated daily with KF through simulated rain at 0, 10, 20, 30 and 40 mg L-1, for 19 consecutive days. Necrosis and chlorosis in S. saponaria were evidenced at the 4th day of KF application, for all treatments, followed by alterations of parenchyma tissues, cell collapse, accumulation of phenolic compounds and damage to the photochemical and biochemical stages of photosynthesis with increasing KF doses. Visible symptoms associated with non-invasive variables, such as F-v/F-m, Delta F/F-m, ETR, A and A/Ci, were shown to be important biomarkers of fluoride action. In addition, the evaluated characteristics indicate that S. saponaria is highly sensitive to KF, with high bioindicator potential regarding this pollutant.