Differential copper toxicity in Amazon tree species explained by seed germination and initial seedling growth

Context

A combination of industrial activities, agricultural practices, and poor urban planning has led to soil and plant contamination throughout the world. Heavy metal stress responses in plants have been demonstrated in various studies, but it remains unclear how heavy metals affect tree germination and initial establishment.

Aims

With a focus on species selection for phytoremediation programs in areas with copper (Cu) soil contamination, we aimed to evaluate seed germination, initial growth, and carbohydrate and protein metabolism of seedlings of Hymenaea courbaril, Stryphnodendron pulcherrimum, and Hevea brasiliensis subjected to normal and high (500 mg kg⁻¹) concentrations of Cu. We hypothesised that there are differences in the Cu effects and plant responses on germination, initial growth, and the metabolism of seedlings from different Amazon tree species.

Methods

The germination experiment was conducted with seeds of the tree forest species in the absence or presence of Cu. After germination-parameter analyses, biometric variables, soluble sugars, starch, and proteins were measured.

Key results

In the presence of Cu, the germination traits, and morphological variables of H. brasiliensis were changed, whereas Cu did not strongly affect the other species. All species showed a high metabolic adjustment capacity, with little impact on the metabolism of carbon and nitrogen-related compounds in seeds. Overall, it was therefore possible to verify that S. pulcherrimum and H. courbaril were able to tolerate Cu because of their good performance in the germination stage and maintenance of essential metabolites, whereas H. brasiliensis was more sensitive to the presence of this heavy metal.

Conclusions

Our results provided insights into the ability of tree species to cope with Cu stress and the hypothesis has been confirmed to interspecific differential tolerance.

Implications

Amazonian tree species show valuable potential for improving phytoremediation programs with a focus on soil contamination by Cu.