Differential Accumulation of Zinc in Selected Plant Functional Types in a Tropical Urban Coastal Wetland: Histochemical Detection and Allocation in Tissues

Zinc (Zn) is an essential microelement of biological processes in plants, such as hormone and protein synthesis, enzyme activation, and carbohydrate metabolism. However, this heavy metal is toxic when soil concentrations exceed 100 mg kg-1. Zn toxicity causes leaf chlorosis, inhibition of root elongation, and reduced metabolic activity. Plants in high Zn-concentration environments have developed diverse mechanisms to sequester excess Zn in organ-specific tissues, such as cell wall immobilization and vacuolar compartmentalization. We chose the heavy metal Zn because preliminary studies on the soil substrates of Ciénaga Las Cucharillas natural reserve found high Zn concentrations. Las Cucharillas is an urban coastal palustrine/estuarine wetland located on the western side of the San Juan Bay in the northern metropolitan area of Puerto Rico. The present study aimed to determine how three dominant wetland species with different plant life-forms physiologically allocate Zn concentrations. We sampled fresh, fully expanded leaves and live, fine roots of