One acorn produces two seedlings in Chinese cork oak Quercus variabilis

Abstract

Although the early germination of white oaks has long been considered an adaptation to counter animal predation, the role of the robust radicles of white oak acorns has been largely neglected in the interaction between acorns and seed-eating animals. Here, the regeneration capabilities of the pruned radicles of intermediate oak Quercus variabilis left by the acorn-eating animals were compared to test the 'one acorn produce two seedlings' hypothesis stating that the remnant radicles exhibit the capability to produce normal seedlings owning to their atypical nutritional and anatomical characteristics. Our results first showed that both pruned radicle and cotyledons from single acorn successfully established seedlings, providing strong evidence on an old puzzle that the robust radicles of early-germinating oak acorns act as reserved propagules, allowing them to escape animals' predation. Our study also suggests that much of the investment in the food reserves of an acorn may be important as a food reward for the animals that disperse the acorns, rather than simply serving as energy for the young seedling.

Nondormant Acorns Show Higher Seed Dispersal Effectiveness Than Dormant Ones

“…Consequently, 40-50% of the cotyledon dry mass was lost 10 weeks after germination. These results coincide with the previous studies on a variety of white oak species [22][23][24]36,37]. Compared to Q. variabilisand Q. serrataproducing nondormant acorns, acorns of Q. accutissima and C. glauca remained dormant and failed to protrude the robust taproots throughout the autumn and winter.…”

“…Our results may have underestimated the possibility of seedling establishment from the nondormant acorns of Q. variabilis and Q. serrata in the field. Our recent studies provide solid evidence that the robust taproots of nondormant oak acorns show the potential to regenerate into normal seedlings even if the cotyledons are detached by seed predators [21,22,24]. However, the taproots of dormant oak species failed to regenerate into normal seedlings [21].…”

“…While seed germination schedules (e.g., delayed seed germination and/or seed dormancy) usually cause seed dispersal differed in time, i.e., temporal dispersal [19,20]. Acorns of most white oak species and some intermediate oaks exhibit no dormancy and germinate rapidly in autumn [21][22][23][24]. In contrast, acorns of red oak species exhibit a delayed germination requiring a period of cold stratification before germination is possible [25].…”

Tracking Animal-Dispersed Seedlings Using 15N Xylem Injection Method

“…However, acorns of Q. variabilis exhibit no dormancy and germinate rapidly after seed fall, generating robust taproots penetrating deep in the soil. Moreover, the robust taproots alone, even without support of cotyledon reserves, show amazing capability to regenerate into normal seedlings (Xiang et al, 2019). Therefore, we predict that the germination schedule and rapid colonization of taproots are highly responsible for the thin-tailed and right-skewed shape of the Q. variabilis seedling distribution than in those species exhibiting fat-tailed distributions.…”

Kinship Analysis and Pedigree Reconstruction of a Natural Regenerated Cork Oak (Quercus suber) Population

“…Identical genotype oaks were located very close to each other, either originating from early sprouts (several decades ago) or multi-seeded acorns resulting from mitotic reproduction of the initial zygote [30][31][32]. Animals such as squirrels could excise the acorns from the soil (or a seed from it) and move them from their original locations to a close spot, explaining the existing distance between each identical genotype oak [33][34][35]. However, when comparing the identical genotypes, which have long been thought to be genetically "identical", small differences were found; they were not 100% identical.…”