The Characteristics Of Plant Community And Its Response To Environment In The Northern Islands Of South China Sea

Vegetation is the main body of the island ecosystem and the structural basis of the island ecosystem.It plays an important role in maintaining the structural stability of the ecosystem and preventing soil erosion.Based on the plant distribution characteristics and environmental factors in 12 plots of five typical island communities in the north of South China Sea,this paper analyzes the differences of basic characteristics,species diversity,plant's functional properties and soil's ecological effects among different islands in the north of South China Sea,explores the main factors influencing vegetation community characteristics and functional properties,understands the ecological adaptability of tropical island vegetation in the north of South China Sea,and clarifies the interaction among the basic characteristics of plant community,plant functional characteristics and environmental factors.Based on the study,this paper aims to provide some reference and basic data for the protection of plant resources,the sustainable development of ecological environment and the ecological restoration of the reclamation island and reef vegetation in the South China Sea.The main results are as follows:1.There are 114 species in 12 quadrats of 5 islands in the north of South China Sea,including 97 species of woody plants and 17 species of herbaceous plants.The herbaceous richness of tropical islands is obviously low.The top three of Damiaodun island accumulated to 70.97%in important value,the top four of Weizhou Island accumulated to 67.85%,and in Dahansandun island,the Casuarina alone amounted to 71.66%.The results show that the dominant species of arbor plants are more prominent in the northern islands of South China Sea,and the most dominant species are Casuarina,Leucaena leucocephala,Fengzi,Melia,and Zingiber officinalis,etc.There is a high correlation between tree diameter class structure and vertical structure,and the differences between them are basically the same in each island.The order of tree size is Dahan Sandun island,Damiaodun island,Weizhou island and Wuzhizhou island.The Shannon Wiener index of Wuzhizhou island is significantly higher than that of other islands(2.994).2.There was no significant difference in the C content of woody plant leaves among the islands.There is obvious correlation between C content and chlorophyll content in leaves,which accords with the theory of"leaf economic spectrum".The content of N and P in plant leaves was 8.73 and 1.64 g/kg,which was lower than that in global terrestrial plants(20.60and 1.99g/kg).The SPAD values of the five islands in the north of the South China Sea are between 36-54,which are slightly higher than the previous values on the coral islands and reefs in the South China Sea.From high to low,the specific leaf area of the plant is in the order of damiaodun island,Weizhou island,Wuzhizhou island,sugarcane island and Dahansandun island.The average leaf thickness of woody plants in different islands is basically opposite to the specific leaf area.The leaf thickness of Ganzhedao island is as high as 0.74mm.3.The average water content of the five islands ranges from 1.13%to 3.5%,with the largest area of Weizhou Island as the maximum.The soil bulk density of Dahan Sandun island is 1.53g/cm~3,which is higher than other islands.The average content of organic matter is 30.58g/kg.the soil salt content of the northern islands is much lower than that of the coastal areas of the Bohai Sea,2.93g/kg,.There was no significant difference in p H value between the islands,no significant difference in TP and AN.Except AK,Except AK,the overall soil nutrient of Weizhou Island is low.There was no significant difference in soil microbial biomass C and P between different islands in the northern South China Sea.The soil microbial biomass C content was 311.86-474.83mg/kg The high-throughput gene sequencing produced 72288 fungi,a total of 14 phyla,41 classes,108 orders,279 families,626 genera and 1036 species.The species composition and diversity index of soil fungi in the study area were quite different in different islands.The Shannon index of Wuzhizhou island was the largest,and its unique species were more abundant.4.TN,MBP,SOM and p H are the most important environmental factors affecting the diameter class structure and vertical structure of the vegetation on Weizhou island.MBN,TN and TK are the main factors affecting the diameter class structure and vertical structure of the vegetation on Wuzhizhou island.And p H,salt content,an and TP are the main factors affecting the basic characteristics of the overall vegetation community of the five islands in the north of South China Sea.On the correlation between the basic characteristics of vegetation community and environmental factors,it was found that soil p H was positively correlated with DBH and tree height(P<0.05),negatively correlated with evenness index(P<0.01),negatively correlated with TP and dominance index(P<0.05),negatively correlated with TN and evenness index,and negatively correlated with an and richness index(P<0.05).5.The most important environmental factors affecting the plant‘s functional properties of Weizhou island are bulk density,MBP and TN.The main factors affecting the plant's functional properties of Wuzhizhou island are TN,an,SOM and salt content.Salt content,TK,TN and LTE are the main factors affecting the overall functional properties of the five islands in the north of the South China Sea.From the specific correlation between the environmental factors and plant's functional properties,it was found that the specific leaf area was negatively correlated with TP(P<0.05)and positively correlated with AK(P<0.05).There was a significant positive correlation between P content and salt content(P<0.01).There was a significant positive correlation between leaf N content and salt content(P<0.05).There was a significant negative correlation between leaf C content and an,salt content(P<0.05).6.It is found that the curve fitting results of different functions are quite different,and the quadratic function has excellent fitting performance in species number area and species number isolation.The results of the study on the relationship between species and area in logarithmic function and power function show that when the island area is small(<5km~2),the number of species on the island increases rapidly,and when the island area is large(5-25km~2),the increase begins to slow down.The number and diversity of species in the quadratic function do not always increase with the increase of the island area,and the number of species will appear repeatedly.It is also found in the regression relationship between isolation and species number that the number of species will appear repeatedly,which is different from the traditional theory of"island effect",showing"Small island effect".