Study On The Competition Between The Plant Spartina Alterniflora And Kandelia Candel In The East Fujian Coastal Wetland

Biological invasion is one of the most important threats to species diversity,ecosystem health and service functions.The coastal ecosystem is the most important buffer zone to withstand global changes,and is one of the high-risk areas for biological invasion.Spartina alterniflora is one of the typical invasive species.At present,many coastal mangrove wetlands in China are faced with the invasion of Spartina alterniflora.East Fujian coastal wetland is the northernmost edge of the distribution of mangroves in China,and only a species of Kandelia Candel.Its habitat is suitable for the propagation of Spartina alterniflora,so that Spartina alterniflora severely damages the ecological environment of the east Fujian coastal wetland,and poses a great threat to the growth of mangroves.Therefore,this paper selects three typical Spartina alterniflora invasive plots of the east Fujian coastal wetland in Xinan town,Yantian town and Wanwu town as the research objects.According to the actual investigation and different invasion degrees of Spartina alterniflora,the Xinan town plot is divided into five mixed proportion communities A,B,C,D and E,the Yantian town is divided into two mixed proportion communities F and G,the Wanwu town is divided into two mixed proportion communities H and I.Through the horizontal and vertical comparisons between different regions and the same region but different Kandelia Candel-Spartina alterniflora mixed proportion communities,to discuss the differences in soil physical properties,plant size of Kandelia Candel and Spartina alterniflora,the distribution of biomass,the competitive effects between Kandelia Candel and Spartina alterniflora within the community,thus revealing the competition between Spartina alterniflora and Kandelia candel,the findings are as follows:(1)There are differences in soil physical properties between the three different regions and different invasiveness of Spartina alterniflora.Overall,the soil moisture content and soil porosity in Xinan town are the largest,followed by Yantian town,and Wanwu town is the smallest,the soil bulk density is the opposite.The maximum soil moisture content is 126.5%,which occurrs in the community of 25%Kandelia candel and 75%Spartina alterniflora in Xinan town,and the minimum soil moisture content is 81.1%,it occurrs in 75%Kandelia candel and 25%Spartina alterniflora community in Wanwu town.The maximum soil porosity is 76.4%,which appears in the single dominant community of Kandelia candel in Xinan town,and the minimum value of soil porosity is 59.1%,it appears in 75%of Kandelia candel and 25%Spartina alterniflora mixed proportion community in Wanwu town.The maximum value of soil bulk density is 1.080 g/cm3,the minimum value is 0.625 g/cm3,the community which appears is to be exactly the opposite of soil porosity.(2)The difference of plant size of Kandelia candel in the same habitat and different mixed proportion community is not significant,but there are significant differences in different habitats.Overall,the habitat of Wanwu town is most suitable for the growth of Kandelia candel,and Spartina alterniflora is obviously inhibited by Kandelia candel in this habitat.Yantian town takes the second place,and Xinan town has the largest competition between Spartina alterniflora and Kandelia candel.Among them,the plant height of Kandelia candel is 1.64m,and the plant height of Spartina alterniflora is 0.83m,the root diameter of Spartina alterniflora is 7.46mm in 50%Kandelia candel-50%Spartina alterniflora community in Xinan town,which are the minimum values in all mixed proportion communities.This shows that when there is a predominance of Kandelia candel(Spartina alterniflora)in the community,a small number of Spartina alterniflora(Kandelia candel)in the habitats can promote the growth of Kandelia candel(Spartina alterniflora).When the ratio of the two species is 1:1,there is fierce competition between the two species and there is a significant inhibitory effect on each other’s growth.(3)The biomass of Spartina alterniflora and Kandelia candel differs in different regions and different mixed ratios.Overall,the biomass of Kandelia candel in Wanwu town is the largest,with an average of 25.57 t/hm2,followed by Yantian town,the mean value is 18.91 t/hm2,and Xinan town is the smallest with an average of 16.06 t/hm2.The biomass allocation of Spartina alterniflora among different regions is completely opposite to that of Kandelia candel,and the total biomass per plant is between 1.81-43.32g.The biomass allocation of Kandelia candel and Spartina alterniflora among the communities shows that the greater the amount of number,the greater the amount of biomass.Among them,the total biomass of Kandelia candel and the total biomass per plant of Spartina alterniflora appears in 75%Kandelia candel-25%Spartina alterniflora community in Wanwu town(27.40 t/hm2)and 75%Spartina alterniflora-25%Kandelia candel community in Xinan town(43.32g).The minimum total biomass of Kandelia candel and the minimum total biomass per plant of Spartina alterniflora are both found in the mixed community of 50%Kandelia candel-50%Spartina alterniflora(14.02 t/hm2,9.00g)in Xinan town.It shows that a small amount of Spartina alterniflora(Kandelia candel)in the habitats can promote the biomass accumulation of Kandelia candel(Spartina alterniflora),but with the increase of the spatial proportion of Spartina alterniflora(Kandelia candel),the biomass accumulation of Kandelia candel(Spartina alterniflora)is gradually decreased.When the two ratios are the same,the biomass accumulation of both species is severely inhibited.Subsequently,as the proportion of Spartina alterniflora(Kandelia candel)increased,the biomass accumulation of Kandelia candel(Spartina alterniflora)is inhibited,but the degree is slightly reduced.(4)The above-ground and underground parts of Kandelia candel-Spartina alterniflora composite community have obvious competition.The above-ground competition effect is more obvious than that of the underground part,and it is in line with the ’total competition effect.In 75%Kandelia candel-25%Spartina alterniflora community,the relative production of Kandelia candel and Spartina alterniflora are 1.156 and 0.700,the total relative-production is 0.928<1,the overall competition balance index are 0.502>0 and-0.502<0,the relative relationship index are 0.072>0 and-0.177<0.In 25%Kandelia candel-75%Spartina alterniflora community,the relative production of Kandelia candel and Spartina alterniflora are 0.945 and 1.057,the total relative production RYT≈1,the overall competition balance index are-0.112<0 and 0.112>0,the relative relationship index are-0.028<0 and 0.028>0.In 50%Kandelia candel-50%Spartina alterniflora community,the relative production of Kandelia candel and Spartina alterniflora are 0.886 and 0.630,all less than 0,the total relative production is 0.748<1,the overall competition balance index are 0.318>0 and-0.318<0,the relative relationship index are-0.072 and-0.227,all less than 0.It shows that when one species is dominant,its competitiveness is stronger,and get another species beneficial effect is greater than the effect of competition.When the space quantity of the two is equal,they have the most obvious interference to the other’s existence,and the competition is most intense.While 25%Kandelia candel-75%Spartina alterniflora composite community presents the phenomenon that two species need the same living resources and both can extrude the other species out of the composite community in a competitive way.(5)Under the mixture ratio of 75%Kandelia candel-25%Spartina alterniflora,Kandelia candel is more competitive than Spartina alternifilora,and gets beneficial effect of Spartina alterniflora is greater than the competition effect,which favors the growth and the biomass accumulation of Kandelia candel.Therefore,it is possible to control the further invasion of Spartina alterniflora by artificial planting to maintain the specific number between Spartina alterniflora and Kandelia candel.