Under arid and semi-arid bioclimates, steppes are increasingly threatened by anthropogenic disturbance and climatic variability, which strongly affects ecosystem functioning and subsequently leads to desertification. We investigated the morphological and physiological responses of Stipa tenacissima L. across three disturbance levels (undisturbed, slightly disturbed, and highly disturbed) in three Tunisian steppe areas (Kasserine, Sidi Bouzid, and Sfax). Morphological and physiological traits were monitored over one year, together with microclimatic variables. Result showed that disturbance was a strong driver of plant functional dynamics, with significant effects on all traits and strong interactions with site and season. Disturbance reduced photosynthetic activity and water use efficiency, particularly in Sfax, where plants adopted conservative strategies (i.e., higher leaf dry matter content and reduced leaf area). In contrast, undisturbed populations maintained a stronger coordination between physiological and morphological traits. Seasonal analyses revealed that disturbance amplified physiological stress with limited recovery. Heatmap analyses further showed that disturbance weakened trait coordination and reshaped trade-offs between acquisitive and conservative traits. Partial least squares-path modeling showed that morphology strongly drove physiological performance (path coefficient=0.48). Disturbance (path coefficient=0.41) and tussock cover (path coefficient=0.47) influenced morphology both directly and indirectly through their effects on physiology. In conclusion, S. tenacissima adjusts physiological and morphological traits under disturbance, favoring stress tolerance, while undisturbed sites maintain high physiological efficiency and coordinated trait integration, reflecting a trade-off between survival and performance while overriding local site differences. Disturbance strongly restructures trait networks, drives site-specific adjustments, and modulates the seasonal balance between morphological stability and physiological flexibility.
Krichen et al. (Wed,) studied this question.