Root morphometry and tolerance of Canna indica in floating treatment wetlands for Cr(III) and Cr(VI) removal

MUFARREGE, M.M.; DI LUCA, G.A.; HADAD, H.R.; MAINE, M.A.; NOCETTI, E.; CAMPAGNOLI, M.A.

Bruges

Simposio; 10th International Symposium on Wetland Pollutant Dynamics and Control, WETPOL; 2023

Ghent University

Floating treatment wetlands (FTWs) consist of a buoyant artificial medium, which facilitates rootdevelopment of plants in the water column. Macrophytes are an essential component of FTWs. Plantspossesses mechanisms to modulate their element acquisition in response to their environmentavailability and demand during their life cycle It is of vital importance to know in depth about theirtolerance and adaptability to survive in an environment different from their natural habitat. The aims ofthis work were to evaluate the changes in root morphometry and tolerance of Canna indica plants andthe implication in the removal efficiency of Cr(III) and Cr(VI) in a FTW. Plants were collected from an unpolluted pond near Santa Fe city, Argentina. The plants were pruned fortheir transport to the greenhouse. Plastic reactors (70 L) containing 4 Kg of sediment and 38 L of tap waterwere installed outdoors under a semi-transparent plastic roof. FTWs consist of a plastic net and had asurface area of 0.10 m2. Buoyancy was provided by a PVC frame. Each raft had a total of 4 plants. The rafts were designed to allow roots hanging in the water column) and rhizomes to remain in the water while aerial parts emerge. After plant acclimatization (about 30 days), fifteen reactors were treated with Cr(III) or Cr(VI) solutions and three were used as biological controls (CB: with FTW, without the additionof experimental solution). Treatments were 5 and 10 mg L-1 of Cr(III), and 5 and 10 mg L-1 of Cr(VI). Also, a biological control (BC) with FTW without Cr addition was used. Water was sampled periodically. Theexperiment lasted 35 days. Cr concentrations in leaves, roots, rhizomes, and sediment were determinedat the end of the experiment. Chlorophyll a concentration was determined at the beginning and the endof the experiment. For the study of the internal morphology of roots; segments close to the base of theroots were extracted. The cross-sectional areas of roots, steel, and metaxylematic vessels were measured,and the number of vessels was counted.Both Cr species were efficiently removed from water in all treatments. The roots were the mainaccumulator organ of this metal and there was translocation to the aerial parts of the plants, beingsignificantly higher in the case of Cr(VI) 10 ppm. A decrease in biomass and chlorophyll concentration wasdetermined in Cr(VI) 10 ppm due to the translocation of this metal. In the Cr(VI) 5 and 10 ppm treatments,the plants showed symptoms of chlorosis. In the histological sections analyzed in the different treatments,significant changes were observed in the morphology of the roots with respect to the BC. The crosssectionalareas of roots were significantly higher in 5 and 10 mg L-1 Cr(III) treatments. Cr(VI) treatments presented the largest vessel area and the lowest vessel number. Plasticity morphology is an importantmechanism for the plant to tolerate harmful conditions. Root modifications allowed C. indica to toleratethe conditions to which it was exposed, without affecting the removal efficiency of the two added Crspecies. The obtained results demonstrated that the use of FTWs populated with C. indica is a promisingtool to remediate water bodies contaminated with Cr.