Seed Germination Of Fraxinus Chinensis Subsp.rhynchophylla Under Indoor Stratification And Natural Burial

Fraxinus chinensis subsp.rhynchophylla,hereafter,F.rhynchophylla is an important economic timber in northeast China.Seeds are the main reproductive material,however,there have not been studied systematically and comprehensively,which leads series problems in seeding,and results poor germination rate or germination every other year.Mature F.rhynchophylla seeds were used as materials to systematically study germination of seeds under cold stratification,autumn burial and spring-summer seeding,which aimed to determine seeds dormancy class,methods for releasing dormancy and appropriate germination temperature.Analyzed physiological and ecological of seeds dormancy and germination,to provide reference for dormancy and germination of Fraxinus and theoretical guidance for seed seedling of F.rhynchophylla seeds.The main research results are as follows:（1）F.rhynchophylla seeds have type 2 non-deep physiological dormancy and condition dormancy,but do not have thermo-dormancy.Mature seeds were water-permeable,and the embryo was fully developed and filled the embryonic cavity.Cold stratification at 5℃ for 8weeks was effective in breaking dormancy,which expanded suitable germination temperature of seeds from 25℃～30℃ to 10℃～30℃.Incubation at a high temperature of 40℃ for 7 days could cause seeds itense decay,which was the critical germination temperature.（2）F.rhynchophylla seeds have transient soil seed bank.Mature seeds fell off in autumn,then entered the litter layer,which lived in next spring germinated better,while seeds then entered the soil layer germinated worse.After temperature rise in June,there was a few seeds still remained in soil seed bank.Most seeds were decomposed and died.With the increase of ambient temperature,seeds sown in early spring continuously germinated and formed seedlings in field,and seeds sown in early summer rapidly germinated and formed seedlings in field.Seeds basically showed germination,seedling or rot in field before high temperature of summer,and proportion of germination and seedling seeds reaches about 80%.（3）Germination of F.rhynchophylla seeds changed with the extension of stratification and burial time.After 8 weeks 5℃ cold stratification,initiation germination time of in vitro embryo was advanced from 5 days to 3 days and final germination rate was increased from 67.67%to96.67%.In vitro embryo sensitivity to ABA was stronger,while GA₃ was weaker.After stratification,the endogenous germination inhibitive activity of de-winged seeds was still high,while that of seed wings was always low.In vitro embryo from soil seed bank had stronger sensitivity to ABA while weaker to GA₃,and high endogenous germination inhibitive activity.With the extension of retention time of seeds in soil,in vitro embryos were slightly more sensitive to GA₃ and less to ABA,and endogenous germination inhibitive activity of seeds increased.In conclusion,F.rhynchophylla seeds have type 2 non-deep physiological dormancy with conditional dormancy,but did not have thermal dormancy.5℃ cold stratification could enhance germination ability of in vitro embryo,and spring sowing could better promote rapid seed emergence.In production,to ensure seeds could germinate smoothly with the rise of temperature in early spring,8 weeks 5℃ cold stratification should be completed in the winter before sowing,which could ensure an even emergence of seedlings and strong seedlings,and improve the success rate of seedling cultivation.