Copper Toxicity on Photosynthetic Responses and Root Morphology of Hymenaea courbaril L. (Caesalpinioideae)

Abstract

Copper (Cu) is a micronutrient essential for plant development. However, in excess, it is toxic to plants and may cause various physiological and morphological changes. The study of the growth of plants exposed to excess Cu is important for the development of phytoremediation programs and for understanding the mechanisms involved in the tolerance of this metal. In this context, the objective of this research was to evaluate the effect of excess copper on photosynthetic responses and root morphology of Hymenaea courbaril L. Biometric measurements, gas exchange, root morphology, and Cu content in tissues and indices (TI and TF) were assessed, involving metal content and biomass. Up to a concentration of 200 mg kg⁻¹, Cu favored growth, gas exchange, and root morphology of the plants under study. At a higher concentration (800 mg kg⁻¹) in the soil, it affected plant growth and caused a decrease in photosynthetic rate. Biochemical limitations in photosynthesis were observed, as well as lower maximum net photosynthetic rate (A_max), respiration rate in the dark (R_d), light compensation point (LCP), light saturation point (LSP), and apparent quantum yield (α), when exposed to excess Cu. Root length, surface area, mean diameter, root volume, dry biomass, and specific root length decreased with high Cu concentrations in the soil. Cu was accumulated in the roots as a mechanism of tolerance to the excess of this metal in order to preserve the most metabolically active tissues present in the leaves. At a concentration of 800 mg kg⁻¹, copper also caused inhibition of the root system. Plants of H. courbaril showed tolerance to excess Cu in the soil and can be indicated for the recovery of areas contaminated with this metal.

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