A review of copper speciation and transformation in plant and soil/wetland systems

Copper (Cu), as a micronutrient and heavy metal contaminant, plays a vital role in the plant and soil/wetland systems. The bioavailability and toxicity of Cu in plant and soil/wetland systems depends critically on its chemical speciation. Several key plant physiological processes are accomplished on the participation and transformation of Cu which is recognized as a cofactor for many plant metalloproteins. Plants tolerate Cu toxicity by immobilizing excess amounts in harvestable parts including leaves, cell walls and vacuolar membrane of root cortex. Concerning environmental Cu bioavailability, plants have evolved different strategies to modulate Cu homeostasis. The immobilized Cu in plants can be remobilized in times of Cu deprivation. Plant Cu acquisition, transportation, and remobilization for growth are managed by several Cu-uptake proteins via Cu transporter COPT/Ctr-like protein family, specific Cu chaperones and metal chelators. The transfer of Cu from soil/wetland systems to plants is determined by the chemical speciation and bioavailability of Cu, which is critically affected by various factors involving plant species, soil microbial community, and dissolved organic carbon, redox potential as well as other soil/sediment physicochemical factors, particular for S cycling and transformation under flooding conditions. Given the increased consumption of Cu products and enhanced concentration of Cu in environment in the past several decades, this review recommends continuous and uninterrupted exploring of the biogeochemical behavior and transformation mechanisms of Cu in plants and soil/wetland systems, particular at the molecular levels.