Study On Embryo Excision Of White Oak Acorns By Small Rodents

Vertebrates play a crucial role in seedling establishment, population regenerationand community succession of various plant species. Nowadays, ecologists in evolutionstudies have focused on the interactions between large-seeded plants and seed-eatinganimals. Non-dormant acorns of most white oaks germinate in autumn soon after seedfall and rapidly transfer the nutrition into the robust taproot; which has been regardedas an adaptive strategy to counter seed predation by animals. To counter rapidgermination and maximize rewards from caches, several species of squirrels have beenidentified to excise the embryo of white oak acorns before storing them, allowinglong-term storage. Although food hoarding animals are challenged by the earlygermination of white oak acorns, acorn embryo excision by other taxa has never beenreported in the interaction between animals and oaks. We also have limited knowledgeabout the response of food hoarding animals to white oak acorns with contrast seedtraits. In this study, we conducted a series of experiments in the semi-naturalenclosures as well as in the field to examine whether other food hoarding animalsinvolve in embryo excision behavior and how they response to acorns with differentseed traits. The results are following:Based on live-trapping and infrared camera capturing, we identified Apodemuspeninsulae, Niviventer confucianus, Cansumys canus and Sciurotamias davidianus asthe main seed predators and dispersers of local white oak acorns. By establishing seedstations on the ground, in cages and on platforms, we found great differences in thefood hoarding behaviour of nocturnal and diurnal animals. A. peninsulae, N.confucianus, and C. canus participated in embryo excision of white oak acorns, whilethe previously reported species S. davidianus did not excise the embryo prior tocaching the acorns.When provided with paired germinating and nongermination acorns of Quercusvariabilis, food hoarding animals tended to eat more germinating acorns, while caching more nongerminating acorns after excising the embryo or pruning the radicles.C. canus pruned less than10%of acorns; however, more than40%acorns in cacheswere radicle-pruned by the other three rodent species. A. peninsulae excised8%ofgerminating acorns but showed no response to nongerminating acorns. We also foundon germinating acorn was embryo excised by N. confucianus.We provided food hoarding animals with nongermination acorns of Q. variabilisand Q. acutissima, to see if they response differently to acorns with differentgermination schedules. Food hoarding animals tended to eat more nondormant acornsof Q. variabilis, while caching more dormant acorns of Q. acutissima. Food hoardinganimals were also found to cache nondormant acorns of Q. variabilis after pruning theradicles. We found3.8%and2.5%of Q. variabilis acorns were embryo excised by A.peninsulae and N. confucianus, respectively. No acorns of Q. acutissima were embryoexcised by food hoarding animals.We also presented acorns of Q. mongolica and Q. aliena var. acutiserrata to foodhoarding animals, to test if they response differently to acorns with different embryodepths. All food hoarding animals but C. canus tended to disperse more acorns of Q.mongolica over Q. aliena. More acorns of Q. mongolica were cached than Q. alienaby A. peninsulae and N. confucianus, while C. canus and S. davidianus showed nopreference for the two acorns. No acorns were embryo excised; however, they weremore likely to be pericarp-removed by A. peninsulae, C. canus and S. davidianus.We collected acorns that were embryo excised or radicle pruned by food hoardinganimals or artificially by observers and planted them in containers together with pairedsound intact acorns, to test the effects of embryo excision and radicle pruning on acornsurvival and then seedling establishment and performance. The embryo excised acornstook longer time to germinate and showed extremely low germination rate. However,there was no significant effect of radicle pruning on acorn survival rate. Artificialexperiments indicated that radicle pruning did not influence germination rates and drymassed of seedling parts (roots and epicotyls). To our expectation, radicle pruningincreased the number of radicles and the ratio of root to shoot, implying that radiclepruning by food hoarding animals may have positive influence on seedlingperformance.