Plant Population Dynamics And Ecological Stoichiometry Of Mangrove In Beilun Estuary In Guangxi

Plants population structure and dynamics are important in the study of population ecology.Researching on plant population structure and dynamics in different regions can not only reflect the survival status of the population,but also can show the plant and environment interaction.It is important in significance for protection and utilization of plant resources.Studying on plant and soil ecological stoichiometry can reveal regulation mechanism of ecological system of plant soil nutrient proportion and their interaction.Understanding the role and nutrient proportion in the process and function of the ecological system.It is very important in climate and geographical variation and adaptation and feedback ability,also can provide guidance to develop a recovery strategy for the vegetation.Mangrove forests,which naturally distribute in tropical and sub-tropical coastal wetland,are woody plant communities and plays a very important role in mangrove wetland ecosystem.Guangxi Beilun Estuary National Nature Reserve has the largest contiguous mangrove ecosystem in China,which provides valuable samples for studying the structure and function of mangrove ecosystem.Twelve permanent plots(each 20m×20m)were set up in the National Natural Reserve of Beilun Estuary in Guangxi.Each plot was divided into 4 contiguous 10m×10m quadrats.All free-standing woody plants,including lianas and vines,base diameter,breast diameter and height were investigated,at the same time the 4 dominant plants(Kandelia candel,Aegiceras corniculatum,Avicennia marina and Bruguiera gymnorrhiza)were sampled in the plot.This study analyzed height class,size class,static life tables,survival curves,time sequences and correlation analysis to describe and predict the population dynamics.In addition,using one-way ANOVA,Pearson correlation analysis and descriptive statistical analysis analysed the characteristics of C,N and P in leaves and soil.The main results and conclusions are as follows:(1)The height structure and size structure analysis indicated that seedlings and saplings of B.gymnorrhiza and K.candel were relatively abundant and that populations showed robust regeneration.Regeneration of A.corniculatum was hindered to some extent,and there were fewer adult plants although the quantity of seedlings and the population overall were relatively stable.There were fewer individuals and no seedlings in the A.marina population,which showed poor regeneration and an obvious decline.(2)The static life table analysis showed that the survival of different age classes of the four mangrove plant species differed greatly,and survival and life expectancy gradually decreased in general with increasing age.The survival curve analysis suggested that the survival curve of A.marina belonged to the Deevey?type,and all individuals reached average physiological life expectancy.The survival curve of B.gymnorrhiza and K.candel belonged to the Deevey ? type,and individuals of different age classes had relatively consistent death rates.The survival curve of A.corniculatum fell between the Deevey?type and the Deevey?type,and the death rates of young age classes were relatively higher and death rates gradually stabilized after the middle-aged phase.Through time sequence analysis,the population of A.marina was predicted to decrease in the future.(3)Time sequence analysis predicted that the number of young individuals of the A.corniculatum population would decrease and that of the adult individuals would increase,and the population size in the future would display a stable trend with a slight decline.Time sequence analysis predicted that the number of young individuals of B.gymnorrhiza and K.candel would be the population size within different age classes would regenerate well;hence,their future population sizes are predicted to increase.Calculation of seven aggregation intensity indexes demonstrated that populations of different age classes of the four mangrove plant species mainly exhibited clumped distributions,and the aggregation intensity always tended to decrease with increasing age.(4)The population dynamics of the four mangrove species and succession stage of the mangrove communities were closely related.The population of the pioneer plant,A.marina,was in a stage of relatively rapid depression,and the population of A.corniculatum,typical of early and middle succession stages,was stable with a slight decline.The populations of B.gymnorrhiza and K.candel,which are typical of middle and late succession,displayed growth of various degrees.These results suggested that the mangrove communities investigated in this study were in the middle stage of succession and that A.marina and the association of A.marina and A.corniculatum will gradually give way to an association dominated by B.gymnorrhiza.The population dynamics of mangrove plants were regulated by multiple factors such as habitat condition,intra-species and inter-species competition,and insect pests.The clumped distribution of the four mangrove plants at different age classes was closely related to their reproduction modes and habitat conditions.The gradual decrease of aggregation intensity with increasing age might be caused by self-thinning or thinning effects resulted from intensified intra-species or inter-species interactions.(5)The foliar C,N and P contents ranged in 421.991-537.920mg/g,9.013-21.633 mg/g and 0.791-3.601 mg/g,with the mean being 492.49mg/g,13.39mg/g and 1.35mg/g,and the foliar C/N,C/P and N/P ranged from 22.76 to 56.73,from 132.66 to 646.81,from 5.56 to 13.01,with the mean being 39.04,132.66 and 10.47.As compared with other research areas,the foliar N/P in the research area was significantly lower.Statistical analysis showed that the variation degree of C/P and C/N was higher than that of N/P in the leaves of 4 dominant mangrove plants.The correlation analysis indicated that there was a significant negative correlation between foliar C and N,C and P,and the foliar N was positively correlated with the foliar P.The N/P value of 4 dominant plant species in the Reserve was less than the critical value of 14,indicating that plant growth was mainly limited by N elements.(6)The soil C,N and P contents ranged in 19.35-39.59 mg/g,0.71-1.73 mg/g,0.14-0.33 mg/g,with the mean being 28.65mg/g,1.04mg/g and 0.22mg/g,and the soil C/N,C/P and N/P ranged from 21.65 to 36.19,from 77.40 to 186.75,from 3.44 to 5.86,with the mean being 28.18,135.21 and 4.77.Statistical analysis indicated that the soil C higher than that the soil C in China,while C/N and C/P were also high,which was related to the strong carbon sink capacity of mangrove ecosystem.The correlation analysis showed that there was a significant correlation between soil C and N,N and P,but there was no significant correlation between soil C and P.The correlation between foliar and soil elements analysis showed that there was a significant correlation between soil P and foliar C,foliar C/P,foliar N/P,as well as soil N and foliar C/P.It have relation with the many factors of plant characteristics,plant growth environment,soil characteristic etc.