| Adiantum nelumboides X.C.Zhang,a perennial evergreen herb,which belongs to the Adiantum of Adiantaceae,is a rare and endangered plant in Three Gorges reservoir region and is also the only single-leaf fern of Adiantaceae that exists in Asia.It is listed as a key protected wild plant and is also one of the eight smallest populations species in Chongqing.A.nelumboides is mainly distributed in the long and narrow sections between the east of Wanzhou and the west of Shizhu county in Chongqing,which are 80~430 m above sea level,100 kilometers long along the river and 3~5 km deep across the two banks.Most of the A.nelumboides grow in steep cliffs and crevices.The number of population and individuals are extremely rare.The distribution scale is small.The habitat is harsh.And the living conditions are extremely severe.In recent years,many of the original distribution areas of A.nelumboides were submerged due to the low altitude with the construction of the Three Gorges Project.The local people also excavated many plants because of their high medicinal value.Based on the influence of many factors mentioned above,the distribution scales and the survival numbers of A.nelumboides are drastically reduced.They are on the verge of extinction.In this paper,we have conducted a detailed record of the living conditions of the existing A.nelumboides through field visits and surveys of the distribution areas of the A.nelumboides.Combining research methods such as floristics,community ecology,and population ecology,we have conducted a comprehensive and systematic study of the A.nelumboides communities.It mainly includes analysis of habitat factors,faunal composition,species diversity,community collocation patterns,niche,interspecific association,spatial distribution pattern,population age structure and dynamics,relationship between populations and environmental factors.We hope to provide theoretical guidance for the rescue and protection of A.nelumboides.The results of the study are as follows:(1)Field surveys were conducted on all the distribution areas of A.nelumboides.Six distribution areas were found.Among them,Hongyanzigou,Shibao Town,Zhong County was the newly discovered distribution areas for the survey.This is the first time that a distribution of A.nelumboides was found in Zhong County.The comparative analysis of distribution areas in 2005,2013,and 2017 shows that the distribution areas of the A.nelumboides are decreasing year by year,many distribution areas gradually disappear.The habitat fragmentation is serious.The existing populations of the A.nelumboides show an isolated " island" distribution.(2)A total of 127 species,112 genera and 71 families were found in the community,among them there were 15 fern species belonging to 14 genera and 12 families,0 gymnosperm specie and 112 angiosperm species belonging to 98 genera and 59 families;The plants of the Compositae and Gramineae contain more species and occupy more advantages in the community.The types of families and genera floristic composition is diverse.The tropical and temperate components are the main components,and the tropical components are dominant.The main life style of the community species is hemicryptophytes,microphanerophytes,nanophanerophytes.The vertical structure of the community is mainly divided into shrub layer and herb layer.In terms of richness index and species diversity index of shrub layer and herb layer,herb layer>shrub layer.(3)The results of heat map analysis of main species in the community in dicated that the important values of the A.nelumboides in the Shuimoxi,Liangshui jing and Wangtianqiu plots were relatively large.The main species composition of the three plots were as follows: Vitex negundo var.cannabifolia+Selaginella mo ellendorffii + Eragrostis ferruginea+A.nelumboides,Debregeasia orientalis+Aspidist ra caespitosa + Selaginella moellendorffii+A.nelumboides,Vitex negundo var.can nabifolia + Selaginella moellendorffii+Drynaria roosii+A.nelumboides.(4)The results of the niche analysis showed that the niche breadth of A.n elumboides(5.373)was the largest among the 25 main species,followed by Selag inella delicatula(5.199)and Artemisia lavandulaefolia(4.728).A.nelumboides and other main species all have niche overlap,and the NO value ranged from 0.292 to 0.974.Among them,the overlapping values of herb such as Selaginella delic atula(0.974)and Veronicastrum stenostachyum(0.819)were relatively large.Amo ng the 300 species pairs of 25 dominant species in the community,there were 88 pairs of low niche overlap(0,1),accounting for 29.34%,and There are 131 p airs of species that have a large degree of overlap(4,5),accounting for 43.67%.Therefore,the ecological heterogeneity among the main species in the communityis small,and the differentiation of resource utilization is not obvious.When the resource supply is insufficient,there will be greater competitive pressure.(5)The method of variance ratio was used to test the overall correlation of the species in A.nelumboides community,and the results showed that the overall correlations of main species in the community showed non–significant positive correlation.It shows that the community is still in an unstable stage.The main reason for the analysis is that human disturbance has impact on the community.In this study,association coefficient(AC),Ochai index(OI),Jaccard index(JI),and chi-square tests were used to analyze the interspecific associations.The results showed that there were 13 species that had a positive association with A.nelumboides,10 species with a negative association,1 species without association,and Selaginella delicatula,Carex brunnea,Cheilosoria chusana,Vitex negundo var.cannabifolia,Rhus chinensis had a strong positive connection with A.nelumboides,but none of them reached the level of significance of the chi-square test.In general,the association between A.nelumboides and other main species in the community was not significant and had a certain degree of independence.(6)The results of spatial distribution pattern analysis showed that the popu lation of A.nelumboides was aggregated distribution because of its own reproducti ve characteristics and the demand for growing environmental conditions.(7)According to the analysis of the main components of 13 environmental factors in each population of A.nelumboides and the correlation analysis of majo r environmental factors and population characteristics,it was found that soil facto rs(total nitrogen,soil moisture content),topographic factors(slope),and human disturbance factors are the main environmental factors that affect the survival and development of A.nelumboidespopulations.The results of the population dynamic s analysis of six plots showed that,the dynamic index of populations in all plot s are greater than zero except Shuimoxi,and the population structure showed a growing type.According to the order of their growth: Hongyanzigou> Pianyan>E rmianyan> Liangshuijing> Wangtianqiu.The Wangtianqiu population structure is c lose to stable.(8)In view of the current endangered status of A.nelumboides,it is necess ary to further strengthen in-situ protection and protect the population of A.nelumb oides and its habitat.The population of Hongyanzigou in Zhong County is sever ely excavated,and the population protection of Ermianyan in Wuling Town is w eak.The population of the Pianyan in Xinxiang Town is near the forest road and vulnerable to human disturbance.Therefore,the protection of these three popul ations should be given more attention.On this basis,appropriate human interventi on was conducted in combination with the study of community characteristics to promote population regeneration and community stability.We should actively carr y out research on in vitro conservation of plant germplasm resource and artificial breeding.A large number of plants can be obtained through spore germination,t issue culture,and artificial cultivation.We should plant these A.nelumboidesin thei r original habitat or historical distribution areas such as Yanshan,Xikou to achie ve enhancement and reestablishment reintroduction,or in different habitats with si milar environmental conditions.Ultimately,these plants grow normally under natural conditions and we can achieve the purpose of protection. |
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