Phylogenetic Diversity Of Angiosperms In Wuling Mountains

Wuling Mountains is a transitional zone from Yunnan-Guizhou Plateau to southeastern hilly plain and the plain of the middle and lower reaches of the Yangtze River.It consists of a series of karst mountain plains and mountains extending arc from southwest to northeast.It extends from south to Miao Mountain,north to Wushan Mountain,east to Xuefeng Mountain and west to Dalou Mountain,including71 counties(cities)in four provinces and cities of Chongqing,Hubei,Hunan and Guizhou,with a total area of more than 170,000 km~2.This study is mainly based on our long-term specimen collections and observations from this area,integrated all data from Wuling Mountain Area Vascular Plant Key,Flora of Hunan Botany,Flora Reipublicae Popularis Sinicae,Flora of China,and other related botanical literatures,as well as the collections of PE,KUN,JIU and the digital information from NSII,CVH,etc.Using the species list and database of angiosperm diversity in Wuling Mountains,the floristic composition,plant diversity pattern and phylogenetic diversity of counties in Wuling Mountains were analyzed to reveal the flora characteristics,formation pattern and maintenance mechanism of species diversity in Wuling Mountains.The main results and conclusions are outlined as follows:(1)Angiosperms are rich in Wuling Mountains with complex composition.There are 178 families,1188 genera and 4920 species of angiosperms in this region,including 176 families,1168 genera and 4889 species of wild angiosperms.The number of this species is less than that of Hengduan Mountains in the same latitude,but it is obviously higher than that of Wugong Mountains and Wuyi Mountains.Asteraceae,Rosaceae and Poaceae are the dominant families in Wuling Mountains.The top 10 families in this region have high similarities with the top 10 families in the same latitude.There are five common families,namely Asteraceae,Rosaceae,Poaceae,Lamiaceae and Fabaceae.(2)The flora of Wuling Mountains is characterized by the transition from subtropical zone to temperate zone.The R/T values of families and genera are 1.83and 1.01,respectively.At the generic level,the proportion of tropical and temperate elements in the flora is similar to that of Hengduan Mountains,Wugong Mountains and Wuyi Mountains.The proportion of Wuyi Mountains is the highest,while that of Hengduan Mountains is the lowest.In addition,the flora of Wuling Mountain also highlights its ancient and unique characteristics.There are not only ancient relicts such as Eucommia ulmoides and Davidia involucrata,but also 111 endemic species(including subspecific units)in Wuling Mountains,such as Chirita briggsioides,Sinosenecio jishouensis,Chirita xinningensis,Aster tianmenshan and Epimedium yinjiangense.(3)The species diversity of Wuling Mountains is not low as a whole.Among the14 counties(cities)in this region,Shimen County of Hunan Province has the highest species richness index,reaching 1971 species;on the contrary,Shizhu County of Chongqing City has the lowest species richness index with 919 species.At the provincial(city)level,the average value of species richness index of counties(cities)in Hunan Province is the largest,reaching 1480 species;on the contrary,the average value of species richness index of Chongqing City is the smallest,reaching 919species.The species similarity coefficients of 14 counties(cities)in Wuling Mountains are higher in the northern region,of which Xuan'en County and Hefeng County in Hubei Province have the highest similarity coefficients,reaching 0.69.In addition,species similarity in Wuling Mountain area shows a positive correlation with geographical distance.(4)The spatial distribution pattern of phylogenetic diversity and species richness in Wuling Mountains is basically the same,showing the trend of high in the northeast,southeast and southwest,and low in the middle.On the contrary,the MPD values of Yanhe County,Longshan County,Yongshun County,Guzhang County,Cili County and Tongren District in the middle of Wuling Mountain are relatively high.In addition,based on the linear model,by combining 19 environmental factors with the phylogenetic diversity of Wuling Mountains,it was found that the most important environmental factors for species richness were the mean temperature in wet season,seasonal temperature and precipitation in dry season.