Study On Reproductive Biology Of Hopea Chinensis

Hopea chinensis is a Grade I priority protection wild tree in China.It belongs to Dipterocarpaceae and the genus Hopea.The populations of H.chinensis are distantly scattered,small in number and narrow in distribution.The species is only distributed in southwestern Guangxi,China and northern Vietnam.It has important scientific and economic values.It provides timber of high quality and is one of China's important resource reserve tree species.According to the field investigation of H.chinensis field,it is found that this tree grows along river banks,and the soil is barren and susceptible to intrusion of river water.The survey found that flowers in each H.chinensis individualare abundant,but the fruit set and seedlings were very limited.Previously research focused on population resources,seed distribution,seed germination,extraction and analysis of genetic material,and physiology and biochemistry of plants.In order to better understand the mechanism of being endangered and carry out protection work,based on previous studies,this studytakes the cultiviatedand wild H.chinensis individuals asmaterials,focusing on flower morphology,breeding system,pollinators,floral odor composition,seed dehydration and germination,seedling growth,and root growth indepth research,by studying the growth and reproduction of H.chinensis,We aim at understanding the pollinationsystem,seed characteristics,seedling and root growth characteristics to find out the causes of being endengered in natural environments,the rarity of seedlings,and provide scientific data for further research on the conservation,introduction and reintroduction of H.chinensis.The following are the main findings of this study:1.Hopea chinensis breeding system,flower visiting insects and flower volatilecompounds.Observation of the flowering phenology of H.chinensis and the visiting insects showed that the anthesis of H.chinensis was about 3 day,and the flowering time of the single inflorescence was about 12 day.Flowering time was 17:00-18:45,duration was about 2 h.In Guangxi Institute of Botany,visitors were only fungus gnat?Mycetophilidae,Bradysia sp.?.The visitation frequency in August and September 2018was 0⁰.73±0.02(visit^-1·flower^-1·h^-1,the average number of visits per flower per hour,the same below),and the frequency of flower visits in August 2019 was 0⁰.05±0.02,the flower visiting insects in Conghuanggou were only fungus gnat,and there were flower visits during the day.There were three species of flower-visiting insects on H.chinensis of Shiwandashan National Forest Park,namely fungus gnat,flies,and bees.The visitation frequency was 0⁰.11±0.01,0⁰.08±0.03,0⁰.24±0.04.The fungus gnat,fly and bee stayed in the flowers for 1 to 2 min,1 min,and 15 s,respectively.In addition,the fungus gnat carried pollen by the abdomen,chest,head,legs,and wings.This study is the first discovery of pollination of fungus gnat in tall trees.H.chinensis are exposed to branches with more light to have flower buds and fruits.The results of testing and analysis of pollen viability,stigma receptivity,pollen ovule ratio,hybridization index,and artificial pollination experiments on H.chinensis showed that the high pollen viability and strong stigma receiptivity stages.H.chinensis natural and hand cross-pollination could lead to fruit production and this species is self-incompatible.The detection of floral odor components showed that the content of olefins accounted for more than 80%of the total.Among them,?E?-7,11-dimethyl-3-methylene-1,6,10-dodecanetriene,?-elemene,and1-caryophyllene account for 25.64±1.60 of the total content,respectively 25.64±1.60%,23.76±3.57%,15.30±1.80%.2.Antenna characteristics of insect visitors to H.chinensis.Fungus gnat are effective pollinators.Because researchers have carried out detailed observations by scanning electron microscopes on bees,this experiment foucused on the antennae and compound eyes of fungus gnats and flies.The results show that there are nine kinds of sensors in the antennae and compound eyes of the fungus gnat,including hair sensor,thorn sensor,cone sensor,cylindrical sensor,ear sensor,tongue sensor and edge sensor.There are two types of sensors in the cavity cone sensor,B?hm mane,fly antennae and compound eyes,which are hair sensor and thorn sensor.3.Fruit diffusion and seed characteristics of H.chinensis.The distance of simulated diffusion of fruits ranges from 0 to 6.5 m.The seeds of H.chinensis are stubborn seeds.The seeds have high water content,and mature seeds can be sown quickly with a germination rate of about 90%.In addition,the water loss rate of seeds is fast,and excessive water loss will cause the seed germination rate to decrease rapidly,even to death.Under natural conditions,the seed germination rate is reduced by half in 5 days,and the germination rate is 0 in about 10 days.H.chinensis has a harsh field habitat,and the ground around adult trees is covered with rocks carried by river flooding.In addition,due to the high quality of H.chinensis wood,the trees have been cut in large numbers,and near this species has been deforestrated for planting cash crops nearby.In recent years,the tourism industry has been vigorously developed,and facilities such as planks and observation decks have been built.These human activities have greatly reduced H.chinensis habitats and are detrimental to its growth,expansion and regeneration.4.Growth of seedlings and young roots on H.chinensis.Among different culture substrate groups,peat soil has the best growth index of seedlings.The above-ground seedling height and dry weight are the largest.The length,surface area,and volume of the underground root system are the best.Among different water content groups,the seedlings and root system indexes are at the optimal value when the water content is 60%,and the seedling height and root index are relatively poor when the water content is 20%and 40%.The seedlings in the compound fertilizer group have the best growth,and the root system indexes are also at the highest quality indicating that sufficient nutrients are needed for seedling growth.According to the growth characteristics of seedlings under different cultivation conditions,they are ranked comprehensively in the order of peat soil,sand?with compound fertilizer added?,sand?water content 60%?,sand?water content 80%?,sand?control?,sand?Water content 40%?,perlite,sand?water content 20%?,yellow mud.