The Study On Seed Propagation Obstacles And Regulation Of Natural Regeneration For Metasequoia Glyptostroboides

Metasequoia glyptostroboides is a famous cypress relic plant in China（according to Flora of China）,and it is a national first-class protected tree species.It was first discovered in Lichuan City,Hubei Province in the 1940s.and was recognized as a major event in the plant kingdom in China and the world in the 20th century.It is known as the“living fossil”in the plant world.The existing Metasequoia glyptostroboides native trees are only distributed in a narrow triangular area between Lichuan City,Hubei Province,Longshan County,Hunan Province,and Shizhu County,Chongqing,with geographical coordinates of 29°44’-30°39’N,108°21’-109°18’E.Through three systematic resource surveys（1997-1998,2006-2007,2017-2018）jointly conducted by Hubei University for Nationalities and Lichuan Metasequoia glyptostroboides Tree Management Station,it was found that there are only 5696 existing Metasequoia glyptostroboides primary mother trees（Lichuan 5663,Hubei,Five plants in Longshan,Hunan,and 28 in Shizhu,Chongqing）,and naturally regenerating Metasequoia glyptostroboides seedlings and saplings are rarely found around the native mother tree and under the forest.This phenomenon has caused academia to explore natural regeneration obstacles and mechanisms of metasequoia Strong interest,but what are the obstacles and mechanisms of Metasequoia natural regeneration are not yet understood and resolved.Based on the general survey of Metasequoia glyptostroboides mother tree resources,this study investigated the seed production of Metasequoia glyptostroboides mother trees,seed germination and temperature and drought stress control tests,appropriate light and density tests for seedling growth,and seed production control experiments of Metasequoia glyptostroboides mother plants.Approaching to explore the reasons for the natural regeneration of the Metasequoia glyptostroboides native tree from the perspective of seed/provenance obstacles,find a way to achieve the natural regeneration of the native Metasequoia glyptostroboides population,and provide technical support for the protection and restoration of the native Metasequoia glyptostroboides population.Research indicates:1.The low seed production of Metasequoia glyptostroboides native populations is one of the factors that makes its natural regeneration bad.Among the 40 primary mother trees core germplasm resources selected in this study,only 7 produced seeds,the yield was only 17.50%,and the average yield was 418.07 g/per.The average yield of 125 33-and 43-year-old Metasequoia mother tree seed orchards（average DBH 38.13 cm）was only 481.09 g/per.2.The aging of the native mother tree of Metasequoia glyptostroboides,low seed vigor and germination rate,are one of the main obstacles to natural regeneration difficulties.The 7 primary mother trees core germplasm resources tested had an average seed germination rate of 19.73%and an average seedling survival rate of 73.42%.And there were significant differences between different mother trees（P<0.05）.The average germination rate of No.1091 mother tree in the indoor temperature and humidity germination test was 41.67%,and the average germination rate of No.2392mother tree in the field experiment was 6.77%.3.The germination temperature and drought stress test of Metasequoia glyptostroboides seeds showed that the average germination rate and germination potential of Metasequoia glyptostroboides seeds under temperature changes were the highest,46.75%and 21.25%,respectively,indicating that the low temperature in native spring is not a factor that makes natural regeneration of Metasequoia glyptostroboides native populations difficult.At the same time,at a temperature of 15°C or 25°C,a low concentration of PEG-6000 solution（0⁰.10 g/mL）can promote the germination potential and germination index of Metasequoia glyptostroboides seeds,and a high concentration（>0.10 g/mL）The PEG-6000 solution inhibited the germination of Metasequoia glyptostroboides seeds,and the inhibition increased with increasing concentration,until the concentration increased to 0.20 g/mL,the seeds of Metasequoia glyptostroboides no longer germinated.4.Metasequoia glyptostroboides seedlings have a relatively high height（ratio of seedling height to ground diameter）under shading conditions.The seedlings are thin and slender,and their growth potential is weak.This indicates that in natural communities,Metasequoia glyptostroboides seedlings grow poorly,and the undergrowth in native populations is weak.May be an obstacle to its natural regeneration.At the same time,in the seeding density gradient set in the experiment,the seed germination rate of Metasequoia glyptostroboides generally increased with the increase of the seeding density,indicating that an appropriate increase in seed seeding volume is beneficial to reserve more effective germinating individuals.5.Through artificial control measures,the yield of Metasequoia glyptostroboides can be increased.The artificial control experiments on 125 and 43-year-old seed plants of Metasequoia glyptostroboides from the 33-year-old and 43-year-old plants showed that the highest seed yield was obtained by ring cutting+trunk injection of 10 mL GA₄₊₇,it is 1992.49 g/per,which was significantly higher than the untreated control group（27.15 g/per）.This indicated that the circumcision and injection of gibberellin on the mother tree could significantly increase the seed yield of the mother tree.At the same time,the seed production of Metasequoia glyptostroboides is closely related to the tree measurement factor.Among the 25 treatments tested,88%of the treated seeds increased with the increase of DBH,and 76%increased with the increase of crown width.To sum up,the main obstacles to the analysis of natural regeneration of Metasequoia glyptostroboides from the perspective of seeds/provenance are:low seed production rate and low seed production rate,poor seed vigor quality,low germination rate,and weak seedling growth potential.At the same time,it was also proved that the low temperature in the native place of Metasequoia glyptostroboides in spring was not the cause of the low seed germination rate.To solve the problem of seed/provenance limitation affecting the natural regeneration of Metasequoia glyptostroboides,artificial control measures can be adopted to increase mother tree seed production,remove undergrowth vegetation,and regulate light intensity to enhance seedling growth.