Patterns Of Plant Diversity And Formation Mechanism In The Kunlun Mountains

Large-scale patterns of biodiversity and the underlying mechanisms that regulate these patterns are one of central topics in biogeography,ecology,and research hotspot of biodiversity.The Qinghai-Tibet Plateau are the natural laboratories for studying these issues.Most previous studies have focused on the entire Qinghai-Tibet Plateau,but the Qinghai-Tibet Plateau consists of multiple physical geographic subunits,which have experienced different geological evolution and uplift history,and the biodiversity pattern and formation mechanism in physical geographic subunits are less well understood.The Kunlun Mountains is a physical geographic subunit located in northwest China on the northern edge of the Qinghai-Tibet Plateau,and ideal areas for studying biodiversity of mountains in the North Temperate Zone,but unclear research of biodiversity pattern and formation mechanism has also been conducted on the areas.The study integrated data of plant species distribution,geological history,related taxa phylogeography in the Kunlun Mountains,and plant species distribution of many high mountain in the world.The study set up 7 databases,and analyzed the floristic similarity,phylogenetic diversity,phylogenetic structure,mean divergence times(MDT),and explored patterns of plant diversity and formation mechanism,and biogeographical roles of the Kunlun Mountains.According to collation and analysis of Flora Kunlunica and related information,a total of 1,911 seed plants have been recorded on the areas,including subspecies and varieties,which belonged to 397 genera,75 families.Gymnosperms are diverse with26 species,5 genera,3 families,whereas angiosperms consist of 1,885 species(including subspecies and varieties),392 genera,72 families.The seed plants of the Kunlun Mountains comprised 226 woody species and 1,685 herbaceous species.5 of these genera are endemic to China,and they are all herbaceous genera of angiosperms.There were 570 species endemic to China,accounting for 29.83% of the total species.By compared with other areas,species richness in the Kunlun Mountains is approximately one sixth of that in the Hengduan Mountains,and a half of that in the Alps Mountains.The Kunlun Mountains are the mountain regions that host low levels of species diversity in the North Temperate Zone.The distribution pattern of phylogenetic diversity(PD),species diversity,and endemic taxa indicates that the east Kunlun Mountains comprise 1,299 species and 493 endemic species,the biodiversity in the eastern regions are observably higher than those in the western regions(813species/51 endemic species),and south slope(602/155)and north slope(639/129)of the central regions.In addition,the mean divergence times(MDT)of the Kunlun Mountains flora indicates that the mean divergence times of the east Kunlun Mountains(MDT = 20.07 Ma)are relatively ancient.Therefore,the east Kunlun Mountains are center of distribution of species diversity,endemic species,and ancient taxa in the Kunlun Mountains.The result of the distribution type of genera suggests that the North Temperate(134genera)and the Old World Temperate(65 genera)have jointly dominated the Kunlun Mountains flora.The distribution type of 75 monophyletic genera indicates that the North Temperate(22 genera)and the East Asia(13 genera)have jointly dominated the flora.The results reveal that the temperate-affinity lineages dominate the Kunlun Mountains flora,also imply that the plant taxa might originate from the Laurasian floras.The analysis of geographical origin of 126 clades indicates that the Kunlun Mountains flora are primarily from East Asian(46 clades)and Tethyan(18 clades)of the Laurasian floras.The floristic similarity indicates that genera similarity is the higher between the Kunlun Mountains and mountains of the North Temperate Zone,whereas species similarity is the highest between the Kunlun Mountains and the Hengduan Mountains(55.94%),the following is the Mountains of Central Asia,and there are little similarity between the Kunlun Mountains flora and the other mountains flora,the results suggest that mass species dispersal occurred between the Kunlun Mountains and the nearby biodiversity hotspots,particularly the Hengduan Mountains.In the Kunlun Mountains flora,94 of the 126 clades originated later than 23 Ma.The mean divergence times(MDT)is early Miocene(19.40 Ma),the median age is 13.75 Ma in the Kunlun Mountains flora.Compared with the median ages of important floras in the North Temperate Zone,the Kunlun Mountains flora is relatively ancient,and their median age is nearest between the Hengduan Mountains flora(13.60 Ma)and the Kunlun Mountains flora,the results imply that they are related.The geological history and mean divergence times(MDT)indicate that current plant taxa primarily originated since the Miocene,current plants composition appear in the Pliocene in the area,and mass species immigration have created the current patterns of plant diversity after glaciations of the Quaternary.Combined with floristic similarity and geographical origin of clades,these results indicate that current plant taxa primarily come from the Tethyan regions,the Mountains of Central Asia,and the Hengduan Mountains,and the Hengduan Mountains is the largest and clear source of species dispersal for the Kunlun Mountains.Based on the patterns of plant diversity formation in the Kunlun Mountains,the nearest taxon index(NTI)of phylogenetic structure indicate that 27 of the 28 countylevel grid units examined were phylogenetically clustered,and only one county-level grid unit was phylogenetically dispersed.The results show that habitat filtering is important driving forces for species migration into the Kunlun Mountains.According to the division of biogeographical roles of mountains,the patterns of plant diversity formation in the Kunlun Mountains indicate that the current biogeographical roles of the Kunlun Mountains are primary corridor,barriers,sink,and the related key processes are species dispersal and extinction.In addition,the Kunlun Mountains is the northern edge of the Qinghai-Tibet Plateau,and also a boundary among East Asiatic,Tethyan,Qinghai-Tibet Plateau,and converted the Qinghai-Tibet Plateau into a relatively closed physical geographical unit.