Seed Dormancy Mechanism And Breaking Methods In Agriophyllum Squarrosum (L.) Moq

The species in dry desert usually has complicated adaptation mechanisms to the environment at the different stage of life history.Seed dormancy with different types and levels is one of the mechanisms that helps the plant to survive and reproduce at the harsh environment.Agriophyllum squarrosum(Amaranthaceae)is widely distributed in the north China and plays an important role in the mobile sand dune fixation.However,the seed dormancy characteristic of A.squarrosum is still not clear and there is limited research on the seedling establishment.Also,the lack of seed production method limits the use of this species during desertification restoration.By conducting experiment both in the laboratory and in the field,the purpose of this research was to study the dormancy mechanism of A.squarrosum and dormancy breaking methods.The seed dormancy release pattern and seed production methods were also investigated.The main results were as follows:(1)The germination percentages of fresh matured seeds in 2 seedlots were <12% at the optimum germination conditions,which means the seeds had severe seed dormancy.Seed coat was proved water-permeable and the embryo was fully developed.Both GA and 4-8 weeks of cold stratification could break seed dormancy.We concluded that seeds of A.squarrosum have nondeep physiological dormancy.(2)With the treatment of fluridone,which is an inhibitor of ABA biosynthesis,seed dormancy broke rapidly and all viable seeds germinated in 3 days.Seed dormancy released gradually with the increase of cold stratification time.By determining the ABA concentration in seeds,seed dormancy release was proved to be consistent with the decrease of ABA in seeds.Thus,ABA is proved to be the key role in the maintain of seed dormancy.(3)With the seed anatomy and tracer element analysis,semi-permeable layer was found in the seed coat which prevented the lanthanum tracer going inside,and also inhibited the ABA leakage to the outside.Seed coat scarification decreased the ABA concentration in the seed and promoted seed germination to >93%.Semi-permeable layer and ABA working together caused the seed dormancy in A.squarrosum.(4)Several plant hormones and chemicals can break dormancy in seeds of A.squarrosum.Treatment with GA4+7 was more effective for seed dormancy breaking than GA3 and ethylene has the highest germination(>90%)percentage and rate.Ethylene treatment was recommended to be an effective method during the seed vigor test.(5)Seed dormancy release in the field showed a seasonal pattern and was influenced by the soil temperature and water content.Seed germination increased from 9%,20%,19% at burial depth of 0,2,5 cm to 20%,28% and 35%,respectively.Seeds were induced into secondary dormancy when the summer season coming with the high temperature and humidity.(6)Seed production was significantly influenced by the times of irrigation and plant density.Seed yield reached the highest,which was 50.5 kg/hm2,with the treatment of 5 times irrigation and 15 kg/hm2 seeding rate,Seed yield was significantly influenced by the yield component of fertile tiller/m2 and spikelet/fertile tiller.During the seedling establishment,seedling emergence percentage was only 8%,and it increased to 31% after 24 h soaking in the 300 ?mol/L ethylene.