Study On The Stability Of Mangrove Seedlings Under The Effects Of Accretion/Erosion Disturbance And Salinity

Mangrove is one of the marine ecosystems with high productivity in the intersecting zone between land and sea in tropical and subtropical coastal zones.Mangrove plays an extremely important role in environmental purification,wind prevention and waves elimination,biodiversity maintenance,carbon sequestration and carbon storage.However,due to the disturbance of a large number of human activities,such as land reclamation and farming,as well as the impact of global climate change,the mangrove ecosystem has been seriously damaged,the area has shrunk,the ecosystem has degraded,and the ecological service function has declined.Therefore,the artificial construction of mangrove wetland and restoration of mangrove ecosystem has become one of the important issues in mangrove study.In the coastal sedimentary environment,the disturbance of accretion/erosion has a significant effect on the coastal plants in the seedling stage.At the same time,salinity is also one of the important factors affecting the growth and development of mangrove seedlings.This study selected typical species as the research object,through the control experiment explore mangrove seedling stability under the condition of tidal flat sediment disturbance and different salinity,for the mangrove restoration in the practice of the choice of tree species and around to provide the reference,also can provide the basis for evaluating the risk evaluation of mangrove species invasion.The experimental results are as follows:(1)The disturbance of accretion/erosion had a significant effect on the survival rate of seedlings.Especially under the condition of erosion disturbance,the survival rate of seedlings decreased greatly.Under different tidal flat disturbance treatments,the survival rate of Bruguiera sexangula was the highest,followed by Brugulera gymnorhiza,Laguncularia racemos,Avicennia marina.The survival rate of Rhizophora stylosa and Aegiceras corniculatum was lower.The disturbance of accretion/erosion had significant effects on the root development of the seedlings of Laguncularia recemos,Avicennia marina,Aegiceras corniculatum and Rhizophora stylosa.The erosion disturbance promoted the root growth of mangrove seedlings,which indicated that the above four seedlings accelerated the root growth and development in order to adapt to the external disturbance so that they could survive in the disturbed environment.As the pioneer species,Laguncularia recemos and Avicennia marina had rapid seedling root growth,so the critical erosion depth of the seedlings was large and the stability of the seedlings was high.There was a significant positive correlation between the critical erosion depth and the root length of seedlings.The longer the root length of seedlings,the deeper the corresponding critical erosion depth,that is,the higher the stability of seedlings.In the case of accretion treatment,the critical erosion depth of six species of mangrove seedlings was compared.The results showed that: Bruguiera sexangula > Avicennia marina >Brugulera gymnorhiza > Laguncularia racemos > Aegiceras corniculatum > Rhizophora stylosa.Under the condition of erosion treatment,the critical erosion depth of 6 species of mangrove seedlings was compared,and the results showed that: Laguncularia racemos >Bruguiera sexangula > Avicennia marina > Brugulera gymnorhiza > Aegiceras corniculatum >Rhizophora stylosa.It can be seen that the species selected for mangrove afforestation in different places should be adapted to local conditions(2)The effects of different salinity on the pioneer mangrove plants Laguncularia racemos and Avicennia marina.It showed that the seedlings of the two pioneer mangrove plants grew normally under the salinity conditions of 0PSU and 15 PSU.However,under the condition of high salinity of 30 PSU,the seedling survival rate decreased significantly,especially the native pioneer Avicennia marina,whose survival rate was only 30% after erosion treatment.The results showed that the tolerance of Avicennia marina to the coupling effect of tidal flat erosion and high salinity was lower than Laguncularia racemos.Under different salinity condition,the erosion and accretion disturbance had significant effects on the root development of both Laguncularia and Avicennia marina.The tidal flat erosion disturbance promoted the root growth of mangrove seedlings,which indicated that seedlings accelerated the root growth and development to adapt to the disturbance environment.With the continuous increase of salinity,the root of seedlings grew slowly,and its response to external disturbance became weak,and its stability decreased,which was not conducive to the early planting of seedlings.There was a significant positive correlation between the critical depth of erosion and the root biomass of the seedlings.The longer the root length of seedlings,the deeper the corresponding critical erosion depth and the higher the stability.The results show that it is reasonable to choose Laguncularia recemos as the species of mangrove area restoration.The root growth rate of the seedlings is fast,and it is more stable and the survival rate is high under both different salinity conditions and accretion/erosion disturbance.Therefore,without considering its ecological risk,it has a certain application prospect in mangrove restoration.