| Mangrove forest is a woody plant community in the intertidal zone of the estuary of tropical and subtropical gulf.It is a common woody plant community in coastal areas of low latitude and is also an important type of wetland ecosystem on earth.Due to the negative impact of the sea level rise and human activities,natural community of mangrove forest has been rapidly reduced,which has become a focus of global ecologist,as well as the research main object of wetland conservation and biodiversity conservation.There are 27 species of mangrove plants naturally distributed in China,among which there are 25 species in Hainan.It is a relatively complete ecological sequence of spatial distribution of mangrove forest from the low tide zone to the high tide zone.Therefore the dynamic change of mangrove community will be the different influenced by plant seedlings growth,due to the simultaneous effects of light,salinity,flooding and other factors in the mangrove forest of Hainan.In this paper,Kandelia obovata,Avicenmia marina,Aegiceras corniculatum,Rhizophora stylosa,Ceriops tagal and Bruguiera sexangula of mangrove forests with different tidal zones in Hainan were selected for experimenting the growth and physiological indicators of seedlings,by artificial simulation control of light intensity,salinity and flooding time.The contents of this study including:(1)the growth and physiological responses of 6 plant species to the single factor action of light intensity,salinity and flooding time;(2)the growth and physiological responses of 6 plant species to the two-factor synergy of light intensity,salinity of sea water and flooding time;(3)the growth and physiological responses of 6 plant species to the synergistic effects of light intensity,salinity and flooding time;(4)the study on these species of ecological niche breadth,overlap and ecological fitness of light intensity,the salinity of sea water and flood time;(5)the main factors affeecting the growth and physiological adaptation of 6 plant species and their adaptation ranges were to studied by principal component analysis,and try to explore the physiological response of different plant species to sea level rise.(6)Under the influence of salinity and flooding time,the transcriptomes in different seedling leaves were analyzed to try to understand the adaptability differences of different seedlings at the molecular level.The result show as follow:(1)The height increment,base diameter increment and biomass increment of all the seedings were incerase with change of light intensity,salinity and flooding time.There is a suitable range and optimum value for light intensity,salinity or flooding time.The higher or lower the value of change of light intensity,salinity and flooding time will cause seedlings grow slowly,stop grow,or death.The seedlings of Kandelia obovata,Avicennia marina and Rhizophora stylosa grow better in natural light environment,the seedlings of Aegiceras corniculatum,Ceriops tagal and Bruguiera sexangula grow better in shade of 20%.It is generally considered that the seedling of mangrove plants grow better needing some fresh watter,our results also show that sea water of 10‰ salinity is advantageous to Kandelia obovata,Ceriops tagal and Bruguiera sexangula,the seedlings of Ceriops tagal and Bruguiera sexangula could grow in the 20-30‰ salinity,but the seedlings grow failure and a small number of death in the 40 ‰ salinity,the seedlings of Kandelia obovata could grow in the 20‰ salinity,but the seedlings grow failure and a small number of death,in the 30 ‰ salinity,and the seedling were all death in 40 ‰ salinity.Therefore,the dilution of sea water is conducive to the seedling growth of Kandelia obovata,Ceriops tagal and Bruguiera sexangula.The seedlings of Aegiceras corniculatum,Avicennia marina and Rhizophora stlosa prefer a salinity environment of 20 ‰.which is beneficial for their growth when the seawater is slightly diluted.However,the seedlings of these plants are also more tolerant of salinity.The different seddlings of mangrove plant species also have different responses to the flooding time.The 12h/d submerged environment is conducive to seedling height,base diameter growth and biomass accumulation of Aegiceras corniculalum,Avicennia marina and Rhizophora stylosa.However,Ceriops tagal and Bruguiera sexangula tend to grow in an environment that is flooded for 8h/d,and in an environment of submerged for 16 h/d,growth failure and a small number of death occur.Therefore,sea level rise or high tide lasts for a long time,which is unfavorable to the growth of Ceriops tagal and Bruguiera sexangula.(2)The influence factors of mangrove seedlings were more complicated than those of terrestrial forest plants,which were not only affected by the light intensity,but also affected by the flooding time and salinity were further confirmed by the results of photosynthetic physiological ecological experiments.We found that the seedlings of Kandelia obovata,Avicennia marina and Rhizophora stylosa were normal in the natural light environment,while the chlorophyll content and photosynthetic rate were normal among our experimental materials.The chlorophyll content and photosynthetic rate of Aegiceras corniculatum,Ceriops tagal and Bruguiera sexangula were normal in 20%shading environment.It can be concluded that Avicennia marina>Aegiceras corniculalum>Rhizophora stylosa>Kandelia obovata>Ceriops tagal>Bruguiera sexangula base on the change of chlorophyll content and photosynthetic rates of these plants for the adaptability of these plants to flooding time.The tolerance of Avicennia marina was the highest,while that of Kandelia obovata was the lowest.lt can be concluded that Avicennia marina>Aegiceras corniculatum>Rhizophora stylosa>Ceriops tagal>Bruguiera sexangula>Kandelia obovata also base on the change of chlorophyll content and photosynthetic rates of these plants for the adaptability of these plants to salinity.(3)According to the measure results of antioxidant enzymes of the seedling leavs,we found that the seedlings of Bruguiera sexangula,Ceriops tagal and Kandelia obovata grow best in 10‰ salnity and 8h/d submerged environment.(There is a slightly different that the optimal environment of seedlings of Kandelia obovata is the 12h/d submerged environment by growth index.Perhaps because the respones of antioxidant enzymes of the seedlings for flooding time is more sensitive.).In the optimal environment,the SOD and CAT activity and MDA content of seedling in leaves were the lowest level.In the normal environment of the other two factors,SOD and CAT activity of seedling leaves of Bruguiera sexangula,Ceriops targal and Kandelia obovata increased first and then decreased with the increase of flooding time.SOD and CAT activity of Ceriops tagal and Kandelia obovata reduce in the 12 h/d flooding environment,while the enzyme activity of Bruguiera sexangula still increase and began to decline by the 16h/d time flooding environment.SOD and CAT activity of the seedlings of Avicennia marina,Aegiceras corniculatum and Rhizophora stylosa were found continus increasing in the flooding range of experimental settings.These results also shows that the seedlings of Avicennia marina,Aegiceras corniculatum and Rhizophora stylosa are quite adaptable to flooding time,and the same results were obtained from the results of growth and photosynthesis(4)The results of the niche width,overlap and niche deviation of the these mangrove plant seedlings were measured by photosynthetic indexes further showed that the adaptability of these mangrove plant seedlings to the flooding time changes was Avicennia marina>Aegiceras corniculatum>Rhizophora stylosa>Kandelia obovata>Ceriops tagal>Bruguiera sexangula;the tolerance of these seedlings to seawater salinity was as follows:Avicennia marina>Aegiceras corniculatum>Rhizophora stylosa>Ceriops tagal>Bruguiera sexangula>Kandelia obovata;the tolerance of these seedlings to light intensity was:Ceriops tagal>Aegiceras corniculatum>Bruguiera sexangula>Rhizophora stylosa>Kandelia obovata>Avicennia marina(5)Combining 10 indexes of seedling growth and physiological ecology,the results of principal component analysis also further showed that the flooded time range of Kandelia obovata,Avicennia marina,Aegiceras corniculatum,Rhizophora stylosa,Ceriops tagal is 2-6 h/d,the critical flooding time is 8h/d,the flooded time range of Bruguiera sexangula is 2-4 h/d,and the upper bound critical time of flooding is 6h/d;the salinity adaptability range of Kandelia obovata,Rhizophora stylosa,Ceriops tagal Bruguiera sexangula is 10?20‰,the upper bound critical value of salinity of seawater is 30 ‰,the suitable range of salinity of Avicennia marina,Aegiceras corniculatum is 10?30 ‰,and the upper bound critical value of salinity of seawater is 40 ‰.The adaptability range of light intensity of Kandelia obovata,Avicennia marina,Rhizophora stylosa,and Bruguiera sexangulais in full light-20%shading environment,and the lower bound critical value of light intensity is 40%shading environment.The adaptive range oflight intensity of corniculatum,Ceriops tagal is full light-40%shadingenvironment,and the lower bound critical value of light intensity is 80%shading environment.In terms of adaptability to sun light,flooding time and slightly,among these 6 plant species seedlings of our experiments,the Ceriops tagal has relatively strong shading resistance,but it is week resistant to long-flooding time and high salinity tolerance;Aegiceras corniculatum has some shading resistance,but it is also relatively resistant to long-flooding time and high salinity tolerance;Avicennia marina has week shading resistance,but it is relatively resistant to long-flooding time and high salinity tolerance;Bruguiera sexangula has some strong shading resistance,but it is week resistant to flooding time and high salinity tolerance;Rhizophora stylosa has some long-flooding time and high salinity resistance,but it is also resistant to some shading tolerance;Kandelia obovata has some shading and long-flooding time resistance,but it isweek resistant to salt tolerance.Our results may be further to showed the mechanism of mangrove forest succession and adapt to sea level rise.Rising sea levels will lead to mangrove ecosystem "retreat to land",But if the land were artificially hardened,it was no space for retreating of mangrove forests.So Bruguiera sexangula,Ceriops tagal will be hurted by Rising sea levels.We suggest that multiple effects such as light factor and water(flooding time or salinity)factor should also be considered in the process of mangrove succession or restoration.(6)Bioinformatics analysis of the leaf transcriptomes of six seedlings treated with different salinity and flooding time by transcriptome analysis showed that under the influence of salinity and flooding time,the transcriptomes of six seedling leaves gene expression differences,the GO functional annotation and enrichment analysis found that gene expression differences are mainly concentrated in the function and cell repair and development related to cell wall organization,external encapsulating structure,extracellular region and the cell wall organization;and energy metabolism first off photosynthesis,light harvesting,chlorophyll binding photosystem I and other types of functions,related species transport secondary active transmembrane transporter activity,plastid membrane active transmembrane transporter activity and other types of functions.At the same time,the KEGG database annotation and enrichment analysis showed that the differentially expressed genes of the six seedlings were mainly enriched with the anabolic pathway of bioactive substances,Flavonoid biosynthesis,Phenylpropanoid biosynthesis,Photosynthesis and Starch and sucrose metabolism related to energy metabolism;Plant hormone signal transduction related to the regulation of physiological processes in plants. |
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