| There are more than 70 species of mangrove plants in the world,of which more than 10 natural hybrids have been reported.For example,the natural mangrove hybrids are mainly Sonneratia x gulngai,Sonneratia x hainanensis and Bruguiera x sexangula.var rhynchopetala in Hainan mangrove forests.Due to negative impact of global climate change and human activities,the natural community area of mangroves has been drastically reduced,and a number of plants,such as the Lumnitzera littorea,Sonneratia X hainanensis and Sonneratia x gulngai,are in imminent danger.Among them,Lumnitzera littorea and natural hybrid Sonneratia x hainanensis have been listed as a national minority population.Though there have been some research work about the suitability of the mangrove plants on the environment,however,the mangrove natural hybrids and parents' adaptability to the environment still lacks research,which is not conducive to the restoration of mangrove natural hybrids.In order to better understand the mangrove natural hybrid adaptability to environment characteristics and propose better protection and restoration measures,it is necessary to carry out a comparative study of related research.As a result,this paper has attempted to select Sonneratia x hainanensis and its parents Sonneratia ovala,Sonneratia alba,Bruguiera x sexangula.var rhynchopetala and its parents Bruguiera gymnorrhiza and Bruguiera sexangula to conducted a comparative study,from the perspective of hybrid advantages and disadvantages,to compare hybrids with those of the parents in the community,population,physiology and molecular level of fitness differences,and to explore the species of mangrove natural hybrid update mechanism,to provide a theoretical basis for the recovery of mangrove forests and endangered plants.The research results were as follows:(1)The relationship of Bruguiera x sexangula.var rhynchopetala as the important values of their parents in the mangrove community in Huiwen Village in Wenchang has been Bruguiera gymnorrhiza(20.55)>Bruguiera sexangula(7.98)>Bruguiera x sexangula.var rhynchopetala(3.72),Bruguiera sexangula(3.84)>Bruguiera x sexangula.var rhynchopetala(2.86)>Bruguiera gymnorrhiza(0.09),Bruguiera gymnorrhiza(9.87)>Bruguiera sexangula(6.06)>Bruguiera × sexangula.var rhynchopetala(4.02),In the mangrove community of Wenchang Puqian,the relationship between their important values has been Bruguiera(21.54)>Bruguiera sexangula(8.11).The importance value and niche of Bruguiera ×sexangula.var rhynchopeiala was inferior to Bruguiera gymnorrhiza and Bruguiera sexangula.However,we have found that among the eight mangrove communities in Wenchang Bamen Bay,Bruguiera x sexangula.var rhynchopetala was biased towards Bruguiera sexangula,and it was also biased towards Bruguiera sexangula in the mangrove communities in Wenchang,indicating that Bruguiera x sexangula.var rhynchopetala 's adaptability to environment was similar to Bruguiera sexangula.Sonneratia x hainanensis appeared in just one location(Wenchang Bamen Bayt).The important value of Sonneratia x hainanensis and her parents in the community of niche was Sonneratia alba(8.08)>Sonneratia ×hainanensis(2.63)>Sonneratia ovata(0.70),Sonneratia alba(4.5)>Sonneratia ×hainanensis(3.01)>Sonneratia ovata(0.97).The hybrid Sonneratia x hainanensis was more inclined to Sonneratia ovata,indicating that the adaptation of Sonneratia x hainanensis to the environment was similar to that of Sonneratia ovata.It was further found in the population structure of Sonneratia alba,Bruguiera gymnorrhiza,Bruguiera sexangula,and Bruguiera x sexangula.var rhynchopetala are all growth type,and their regeneration succession was better,while Sonneratia x hainanensis and Sonneratia ovata are recession type,and the population would be reduced.(2)Through germination of natural hybrid and parent seeds(hypocotyls),we have found:Through the experiment of controlling illumination time,temperature and salinity,the germination indexes of Sonneratia x hainanensis and its parents have showed that there were different suitable ranges and optimal values with the changes of illumination time,temperature and salinity.Three kinds of plant seed germination need to extend the illumination time,high temperature and salinity,light 12 h,the temperature 35?,the best of 2.5‰ salinity.When the temperature was too high or too low,it would have obvious influence on germination of seeds,the appropriate temperature of Sonneratia alba seed germination is 25 to 40?,the optimum temperature 35?,appropriate Temperature of Sonneratia x hainanensis and Sonneratia ovata seed was30 to 40?.Adaptiveness of the seed germination to temperature was Sonneratia alba>Sonneratia ovata>Sonneratia x hainanensis.The suitable salinity range for Sonneratia alba was 0-15‰;the suitable Salinity range for Sonneratia x hainanensis and Sonneratia ovata was 0-7.5‰.It has been concluded that the adaptability of their seed germination to salinity in order was Sonneratia alba>Sonneratia x hainanensis(Sonneratia ovata).This was consistent with the results of Sonneratia x hainanensis and Sonneratia ovata in the low salinity of Bamen Bay areas.The results have showed that the environmental adaptability of the natural hybrids Sonneratia x hainanensis seed was lower than that of the parents Sonneratia alba and Sonneratia ovata,which showed some hybrid vigor.The growth index has showed that there were different suitable ranges and optimum values with the changes of shading intensity,salinity and waterlogging time,and the change of environmental conditions too high or too low would affect the initial germination date,germination cycle,germination rate and mortality of the hypocotyl.The suitable range of shade intensity of Bruguiera gymnorrhiza was 0-60%,the best shade intensity was 20%.But certain shading intensity was more beneficial to germination,the suitable range of shade intensity of Bruguiera x sexangula.var rhynchopetala and Bruguiera sexangula was 0-40%.The adaptability of hypocotyl germination to shading in order was found to be Bruguiera gymnorrhiza>Bruguiera × sexangula.var rhynchopetala>Bruguiera sexangula.The salinity of Bruguiera gymnorrhiza was 0-30‰,the most suitable was 10‰,the salinity of Bruguiera sexangula was 0-25‰,the salinity of Bruguiera sexangula was 0-20‰,and the most suitable was 5‰.The hypocotyls germination of the three species were all subject to certain waterlogging,while 0 to 12 hours of waterlogging per day was suitable for Bruguiera gymnorrhiza hypocotyl germination,and 8h/d was the best.The waterlogging time range of Bruguiera x sexangula,var rhynchopetala and Bruguiera sexangula was slightly shorter,0 to 8h/d,and 4h/d was the best waterlogging time.After comprehensive analysis,the adaptation size of hypocotyl germination to submergence was found to be Bruguiera gymnorrhiza>Bruguiera× sexangula.var rhynchopetala>Bruguiera sexangula.The results of the adaptability study of the above three environmental conditions have indicated that the cotyledon of the natural hybrid Bruguiera × sexangula.var rhynchopetala had an environmental adaptability between Bruguiera gymnorrhiza and Bruguiera sexangula,and preferred Bruguiera sexangula.(3)The growth experiment of natural hybrid and parent seedlings has found that:Through three-factor experiment of illumination,salinity and waterlogging,Sonneratia x hainanensis and its parent seedlings' physiological growth index showed different suitable range and optimum value with the change of shading intensity,salinity and waterlogging time.The adaptive range of Sonneratia alba and Sonneratia ovata to shading was 0-40%.But the Sonneratia alba was more shade tolerant,with an optimal shading intensity of 20%,while the Sonneratia ovata has had an optimal shading intensity of 0%.The adaptive range of Sonneratia x hainanensis to shading was 0-20%.Their shading adaptation in order is Sonneratia alba>Sonneratia ovata>Sonneratia ×hainanensis.The Salinity range for Sonneratia ovata was 0-10‰,while the optimum Salinity was 5‰.The salt-tolerant of the three species in order was identified as Sonneratia alba>Sonneratia ovata>Sonneratia x hainanensis.The seedlings of the three plants' adaptation of waterlogging time range was 0-8h/d,the best waterlogging time range was 0-8h/d,The waterlogging adaptability of the three species in order was Sonneratia alba>Sonneratia ovata>Sonneratia x hainanensis.The results showed that the environmental adaptability of the natural hybrids Sonneratia × Phainanensis seedlings was lower than that of the parents Sonneratia alba and Sonneratia ovata.The shading range of Bruguiera gymnorrhiza and Bruguiera x sexangula.var rhynchopetala was 0-40%,with the optimal shading intensity of 20%.Principal component analysis has showed that the salinity range of the three species was 0-20‰,Bruguiera gymnorrhiza was better tolerant to salinity,the best salinity of Bruguiera gymnorrhiza was 15‰,and the best salinity of Bruguiera sexangular.var and Bruguiera sexangula was 10‰.The salt-tolerant of the three species in order was Bruguiera gymnorrhiza>Bruguiera x sexangula.var rhynchopetala.The best waterlogging time of Bruguiera gymnorrhiza and Bruguiera x sexangula.var thynchopetala is both 8h/d,while the waterlogging time range of gymnorrhiza is more flood-resistant,and the adaptive waterlogging time range is 0-12h/d.The waterlogging time range of Bruguiera x sexangula.var rhynchopetala and Bruguiera sexangula were the same,0-8h/d,but the best waterlogging time of Bruguiera sexangula was 4h/d.The size of the waterlogging tolerance of the three species in order was Bruguiera gymnorrhiza>Bruguiera x sexangula.var rhynchopetala>Bruguiera sexangula.The results of the adaptability study of the above three environmental conditions all indicated that the seedling of the natural hybrid Bruguiera x sexangula.var rhynchopetala had an environmental adaptability between the parents Bruguiera gymnorrhiza and Bruguiera sexangula,and preferred Bruguiera sexangula.(4)Leaf transcriptome analysis of natural hybrids and parent seedlings under salinity and waterlogging stress:It has carried out bioinformatics analysis of the leaf transcripts of different salinity and waterlogging time hybrids Sonneratia x hainanensis,Bruguiera × sexangula.var rhynchopetala and six plant seedlings of parent.Results showed that under salinity and waterlogging stress,GO functional annotations have showed that differently expressed genes was found mainly in protein binding,Catalytic activity,Cellular process,Metabolic process,Cell,Cell part,Membrane,Membrane part,Organelle,and Single-organism process,etc.Found by the KEEP annotation,6 kinds of seedlings of differentially expressed genes was mainly enriched in the pathways of Metabolism,Genetic Information Processing,Environmental Information Processing,Cellular Processes,Organismal Systems,and Human disease.Based on the analysis of community and population characteristics,the status of natural hybrid Sonneratia x hainanensis and its parents,natural hybrid Bruguiera ×sexangula.var rhynchopetala and its parents in the community were preliminarily determined in this study.Through the experiment of seed germination and seedling growth environment control,it was verified that the adaptability of natural hybrid Sonneratia x hainanensis to the environment was lower than that of its parents,Sonneratia alba and Sonneratia ovata,which showed some hybrid weakness.Salinity might be one of the key factors in the distribution of the natural hybrids Sonneratia x hainanensis and its parent Sonneratia ovata,which are distributed only in Bamen Bay areas.The adaptability to environment of Bruguiera sexangula was lower than that of Bruguiera gymnorrhiza,and higher than that of Bruguiera sexangula,and more inclined to Bruguiera sexangula.Results of environment control experiment and the analysis of characteristics of community and species were not completely consistent,probably because there were many influenced factors in community structure and population growth.So,environmental conditions was one of the important factors affecting mangrove natural hybrids and their parent population development.The adaptability to the environment has affected the status of mangrove natural hybrids and their parents in the community. |
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