Climatic conditions and herbivory effects on morphological plasticity of Argania spinosa.

The main objective of this paper was to look into the morphological differentiation patterns and phenotypic plasticity in four populations of Argania spinosa with environmentally contrasted conditions. Mean response, magnitude and pattern of morphological intra- and inter-population plasticity indexes were measured and analyzed in order to identify which characters contribute the most to the acclimation of this species. Populations growing in the ecological optimum of the species presented the lowest plasticity, while those growing in the most stressed habitats showed an increased morphological variability. The study of four populations showed that human pressure seems to play an important function in the regulation of morphological characters. However, climatic conditions seem to play a significant role in the increase of morphological plasticity.

Some secrets of Argania spinosa water economy in a semiarid climate.

Argania spinosa is an example of an avoider tree growing under semi-arid conditions in Morocco. To assess what are the physiological strategies of this species, different variables were measured through an annual cycle in two populations located in the species' main distribution area. Results show the expected decrease of leaf water potential (psi) with an increase of water-use efficiency (A/gs) with the onset of the dry season. In summer, leaf conductance (g(s)) was sensitive to vapour pressure deficit (VPD), and stomatal closure occurred over 30 mbar of VPD. Surprisingly, carbon isotope discrimination (delta13C) maintained very low values over the year, with almost no relationship with any physiological or morphological variable. Hence Argania spinosa presents a complex set of mechanisms to avoid water deficit, but delta13C cannot be used as an ecological tracer of long term WUE.

Germination success and seedling development of Argania spinosa under different climatic conditions and browsing intensity.

The present study assesses whether the germination and establishment success of Argania spinosa seeds are affected by the environmental conditions under which the mother plant has grown. Seeds from three populations with different climatic conditions and herbivory intensity were collected and sown in the laboratory after different treatments. Our study suggests that the seed germination process and initial stages of seedling growth are adaptive. Seeds from the population of Agadir with the highest herbivory pressure and high air relative humidity in summer (due to the proximity to the sea) were stimulated by acid treatment, and showed a lower root/stem ratio, which allows them to take advantage of the atmospheric water resources. Seeds from the Mountain population, where the most arid environmental conditions were found, produced early-germinating seeds with the highest root/stem ratio that would facilitate seedling establishment when the harshest environmental conditions appear in summer.