Trade-offs of different types of dose-responses following temporal gradients of Pb stress in Tillandsia usneoides.

This article investigates the dose-response relationships of lead (Pb) stress over time in the indicator plant *Tillandsia usneoides*, focusing on five damage biomarkers and eight resistance biomarkers. Using fixed 1 mM Pb concentration with either five or ten temporal gradients, the study found that nonlinear responses—including monophasic, biphasic, and multiphasic patterns—occurred, with multiphasic responses becoming more detectable as the number of time gradients increased. The research also applied trade-off theory, distinguishing two types: trade-off 1 (toxicants worsen some markers while stimulating others) and trade-off 2 (toxicants do not affect some markers but stimulate others), revealing that trade-off 2 was more frequent, especially among resistance biomarkers. These findings suggest that *T. usneoides* coordinates resistance mechanisms over prolonged Pb exposure to maintain internal balance, and that trade-off theory provides a useful framework for understanding complex toxicant-organism interactions. The study emphasizes the importance of considering multiple dose gradients and nonlinear responses in toxicological risk assessment.