Understanding how plants respond to stress gradients remains a central challenge in plant ecology. While it is often expected that mean values of stress-related traits shift systematically along such gradients, patterns of trait variation within populations are less predictable. On one hand, increasing stress may reduce within-population variation. On the other, if plants cope through flexible responses, variation may increase – especially when stress coincides with environmental unpredictability. Clarifying these patterns is key to understanding the role of plasticity and how its expression varies along stress gradients.
I used Anastatica hierochuntica, an annual desert plant known for its tolerance to extreme conditions, to test whether (a) mean values of physiological and phenological traits vary along aridity and salinity gradients, and (b) phenotypic plasticity in these traits differs across the gradients. Seeds were collected from 10 populations along natural stress gradients and grown under a factorial design combining high/low watering and salinity treatments.
Results showed no consistent shifts in mean physical trait values across the gradients. However, phenological traits—leaf emergence, flowering, fruiting, and longevity—exhibited significant intrapopulation variation in response to treatments. In contrast, physiological traits such as osmotic potential and relative water content were more stable.
These findings suggest that A. hierochuntica maintains flexible, individual-level responses to stress, allowing rapid adjustment to fluctuating conditions. Phenological shifts appear to be the primary axis of this response, reflecting adaptation not only to stress intensity but also to environmental unpredictability.
