Background and Aims
Oaks are the foundation and dominant tree species of most Mediterranean forests. As climate models predict dramatic changes in the Mediterranean basin, a better understanding of the ecophysiology of seed persistence and germination in oaks could help define their regeneration niches. Tunisian oaks occupy distinct geographical areas, which differ in their rainfall and temperature regimes, and are thus a valuable model to investigate relationships between seed traits and species ecological requirements.
Methods
Seed morphological traits, desiccation sensitivity level, lethal freezing temperature, embryonic axis and cotyledon sugar and lipid composition, and seed and acorn germination rates at various constant temperatures were measured in Quercus canariensis, Q. coccifera, Q. ilex and Q. suber, using seeds sampled in 22 Tunisian woodlands.
Key Results
Only faint differences were observed for desiccation sensitivity in the oak species studied. By contrast, the species differed significantly in sensitivity to freezing, germination rates at low temperature and base temperature. Quercus ilex and Q. canariensis, which occur at high elevations where frost events are frequent, showed the lowest freezing sensitivity. A significant correlation was found between hexose contents in the embryonic axis and freezing tolerance. Significant interspecific differences in the time for seeds to germinate and the time for the radicle to pierce the pericarp were observed. The ratio of pericarp mass to acorn mass differed significantly among the species and was negatively correlated with the acorn germination rate. Quercus coccifera, which is frequent in warm and arid environments, showed the highest acorn germination rate and synchrony.
Conclusions
Seed lethal temperature, seed germination time at low temperatures, the ratio of pericarp mass to acorn mass and the embryonic axis hexose content appeared to be key functional traits that may influence the geographical ranges and ecological requirements of Mediterranean oaks in Tunisia.
For the first time, the current study was designed to evaluate growing location on the chemical composition as well as the DPPH capacity of Crataegus azarolus L. (var. aronia (Willd.) Batt.) methanolic aqueous extracts. It was found that Crataegus azarolus L. collected from Neber (Governorate of Kef) had the highest total phenolic, flavonoids, condensed and hydrolysable tannin contents while the same genus growing in Jdidi (Governorate of Zaghouan) were characterized by the highest content of sugar (15.27 mg Gluc g −1 DW). Moreover, the plants contents' in P, K, and Na was investigated. Accordingly, the genus origins have shown to highly affect their content in the former minerals. In vitro, antioxidant activity was also determined using DPPH radical and expressed as concentration of each extract in order to inhibit 50% of DPPH radicals. The obtained values ranged from 55.22 to 138.66 μg mL −1 . From a nutritional and antioxidant point of view, Crataegus azarolus L. (var. aronia (Willd.) Batt.) can be considered as a valuable variety.
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