The Evolutionary Model And Ecological Adaptation Mechanism Of Quercus Section Cyclobalanopsis Based On Seed Functional Traits

A seed is a special reproductive organ of seed plants and it is a plant body in another form.The functional characteristics of seeds mainly include size,dormancy types,and germination characteristics,which are closely related to the success of seed construction.Therefore,the functional characteristics of seeds are a key factor in determining the survival and extinction of species.Quercus section Cyclobalanopsis is one of the representative specie of evergreen broad-leaved forests in the tropical and subtropical monsoon regions of East and Southeast Asia,and has very important ecological and economic value.At present,the species formation and distribution pattern of section Cyclobalanopsis are not clear.This study aimed to reveal the evolutionary history of section Cyclobalanopsis and its influence on species diversity through its seed functional characteristics.Based on the existing stable phylogenetic tree,the data were first collected on the functional traits of 31 species of the section Cyclobalanopsis group;second,we supplemented the experiment of the seed functional traits of five species of section Cyclobalanopsis group with missing data;and finally,based on the phylogenetic tree,the evolutionary pattern of the seed functional traits and their impact on species distribution pattern were discussed by reconstructing ancestral traits and mapping stochastic traits,and combining these with species diversity.The results showed that:(1)the fruits of section Cyclobalanopsis are the carrier of seed transmission and dispersal,and are composed of woody exocarp,brown fibrous endocarp and seed;seeds have fully developed mature embryos.(2)In the process of seed germination,the radicles of Quercus chungii and Q.rex had no dormancy but their epicotyl had obvious physiological dormancy;therefore,the seed dormancy type of the two species was a medium depth physiological dormancy.However,the pericarp of Q.sessilifolia and Q.multinervis obstructed the water absorption of the seeds and significantly affected seed germination;therefore,the dormancy type of these two species is physical dormancy.Seed germination of Q.gilva is the most difficult.It not only has physical dormancy,but also has obvious physiological dormancy on its epicotyl.Therefore,Q.gilva has a typical type of comprehensive dormancy.Research on the evolution of the seed functional characters found that:(1)small fruit,2-year mature fruit,hypocotyl close to fruit apex,traditional cotyledon petiole,and physiological dormancy are the ancestral traits of section Cyclobalanopsis.(2)With the evolution of the characters,the small fruit evolved into medium fruit and large fruit,and the fruit matured from 2 years to 1 year;however,the ancestral characters of the fruit shape(ellipsoid/oblate)are unknown.(3)The embryo germinated from the near apex to the near hilum,and the cotyledon elongation evolved from the traditional cotyledon.(4)Physical dormancy,non-dormancy,epicotyl physiological dormancy and comprehensive dormancy are the results of the adaptive evolution of species to specific environments.The above results show that the diversity of seed function and shape is high in the section Cyclobalanopsis,which plays an important role in species distribution and diversification.First,the seed dormancy types of section Cyclobalanopsis plants are diverse.We speculate that this is the different adaptive evolutionary characteristics of different species to the local climate after they spread to their distribution areas.Second,the small fruit plants are conducive to carrying and dispersion by animals,thus promoting the speciation and diversification of evolutionary branches.Third,the possibility of species hybridization and the rate of generation replacement of plants with one-year mature fruits significantly accelerated the diversification of species and the formation of new species.In addition,fruit germination near the hilum,cotyledon petiole elongation,and non-dormancy of roots seem to be a group of adaptive evolutionary characteristics of section Cyclobalanopsis plants to specific environments,which can increase the probability of successful seedling establishment under drought or animal grazing conditions.In conclusion,changes in the seed functional traits,such as seed size,cotyledon petiole morphology and dormancy morphology,have important ecological significance in the establishment and maintenance of populations,especially in a changing and unstable environment,and may even play an important role in the success of species evolution and the improvement of species diversity.