Reacclimation

Reacclimation refers to the re-establishment of an acclimated state after an organism has experienced a change in conditions that caused the loss or reduction of its prior acclimation. It describes how plants, animals, and humans regain enhanced tolerance or performance when re-exposed to the same stressor after a period away from it. Reacclimation is distinguished from initial acclimation, though the underlying physiological processes are often similar and involve memory-like responses that streamline responses on subsequent exposures.

Common mechanisms include reactivation of protective pathways activated during the first acclimation, such as heat shock proteins, antioxidant systems, osmolyte accumulation, and metabolic adjustments. Epigenetic changes and alterations in sensor signaling may also facilitate faster or stronger responses upon reacclimation. The time required for reacclimation varies with species, stressor, and environmental history.

In plants, reacclimation to drought, cold, or heat can occur after seasonal changes, and prior exposure can influence the magnitude and speed of subsequent tolerance. In humans, prior exposure to heat, altitude, or exercise can enable faster re-acquisition of tolerance or performance upon re-exposure. In wildlife, repeated exposure to fluctuating temperatures or salinity can lead to more rapid physiological adjustments when conditions return.

Reacclimation has implications for agriculture, climate resilience, and human performance, informing crop management, training schedules, and models of organismal response to changing environments. It remains an active area of study to distinguish reacclimation from deacclimation and to quantify its limits and mechanisms across taxa.