Variation in seed traits among Mediterranean oaks in Tunisia and their ecological significance

Abstract

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.

Climate drives patterns of seed traits in Quercus species across China

“…In Mediterranean areas, temperate oak seeds disperse in warmer and wetter winter conditions ( c . 9°C, 355 mm) (Amimi et al ., 2020). These species had similar desiccation tolerance to Chinese temperate oaks, but many species germinated faster (Ganatsas & Tsakaldimi, 2013; Joët et al ., 2013; Xia et al ., 2015; Amimi et al ., 2020).…”

“…9°C, 355 mm) (Amimi et al ., 2020). These species had similar desiccation tolerance to Chinese temperate oaks, but many species germinated faster (Ganatsas & Tsakaldimi, 2013; Joët et al ., 2013; Xia et al ., 2015; Amimi et al ., 2020). Typically, Q .…”

“…Furthermore, oak seeds of arid region species tend to dry more slowly (Xia et al ., 2012a,b). Whilst temperate oaks from Mediterranean areas showed high potential for germination at low temperatures (5°C) (Amimi et al ., 2020), some subtropical evergreen oaks germinate poorly at temperatures as high as 15°C (Xia et al ., 2015). These studies imply that there may be relationships between seed traits and species habitats, but their results are inconclusive.…”

Interspecific Variation between the American Quercus virginiana and Mediterranean Quercus Species in Terms of Seed Nutritional Composition, Phytochemical Content, and Antioxidant Activity

“…Forest trees have enormous economic and ecological importance worldwide, but they will be seriously affected by climate change [ 1 ]. Principally, those species producing recalcitrant seeds will be particularly susceptible to the increasing intensity and frequency of drought episodes predicted by global climate changes [ 2 ]. In this context, one group of forest plants that could be affected is the Quercus genus, whose seeds are recalcitrant, and it grows in areas where models have predicted climate changes.…”

Characterization of physiological traits during development of the recalcitrant seeds of Quercus serrata

“…Q. serrata has a wide distribution throughout northern and southern China, spanning an area of 18°4' to 36°6' latitude and 102°23' to 120°28' longitude (Huang et al 1999;NPSRC 2020). Seeds of many Quercus species are reported to be recalcitrant, since they are sensitive to desiccation (Finch-Savage et al 1992;Xia et al 2012;Amimi et al 2020). While there is no record for the seed desiccation tolerance of Q. serrata, the wide distribution and variable habitats may influence seed development of this species and therefore lead to variations in seed traits, including the level of desiccation tolerance in different habitats.…”