Distribution Of Parasitic Angiosperms And The Parasite-host Interactions In China

Approximately 4,500 species of angiosperms(more than 1% of all)are parasitic all over the world.These parasitic plants have irreplaceable ecological value,obtaining partial or entire water and nutrients from host plants through their specialist structure "haustorium".This paper focuses on a further study of parasitic angiosperms in China from the perspectives of species distribution and interaction.China is rich in parasitic angiosperm species,with these plants widely distributed in all provincial administrative units.More recently,some new parasitic plants have been reported.However,the spatial distribution and influencing factors of different parasitic types have not been studied.Therefore,we first updated the checklist of parasitic angiosperms in China.On this basis,the distribution patterns of four parasitic types(root vs stem parasites,hemiparasites vs holoparasites)and total parasitic plants were mapped.22 environmental factors representing biotic,topographic and climatic factors were selected to determine the leading factors of those various distribution patterns by multiple stepwise linear regression analysis and redundancy analysis.It can help to further understand the interplay of biotic and abiotic factors in the formation and distribution of parasitic plants,and to provide a scientific basis for effective management and ecological conservation on these plants.Theoretically,global warming will alter the current distribution of parasitic plants and as well as their hosts,then reorganize their distribution maps.In this paper,maximum entropy model was used to predict the distribution of four parasitic plants(Cynomorium songaricum,Boschniakia rossica,Cistanche deserticola and Cistanche mongolica)and their main hosts(Nitraria sibirica,Alnus mandshurica,Haloxylon ammodendron and Tamarix ramosissima,relatively)under current and future climate scenarios.The suitable habitat changes of these parasitic plants under global warming and the distribution differences between parasites and their hosts were analyzed.This can provide reference for the protection of the wild resources of these rare medicinal parasitic plants.In addition,a phylogenetic interaction network between Loranthaceae plants and their hosts at the genus level was constructed in this paper by using electronic specimens.Host specificity was then analyzed in terms of host richness and evenness;the host overlap among eight parasitic genera was calculated;and the phylogenetic relationship between parasitic plants and their hosts was also analyzed.These analyses can help to better understand those underlying processes that are responsible for the development and maintenance of host specificity.The main research results of this paper are as follows:(1)Distribution patterns and influencing factors of different parasitic angiosperm types(1)According to APG IV,a total of 745 parasitic angiosperms belonging to 12 families and 50 genera were naturally distributed in China.(2)Different parasitic types varied quite distinctly in terms of distribution patterns across China..Regarding root parasites and hemiparasites,most of them appeared in the east of China than in the west.Stem parasites showed a broader north-south divide in distribution.Additionally,holoparasites displayed a patchy distribution.The evolutionary relationships and different life strategies may account for the different geographic distribution patterns of different parasitic types in China.(3)Parasitic angiosperms in China were mainly affected by the biotic factor,temperature,and precipitation.Seed plant richness(SPR)was one of the common leading factors affecting the distributions of root parasites,stem parasites,and hemiparasites.Besides,the other major influencing factors were the maximum temperature of the warmest month(Bio5),temperature seasonality(Bio4)and precipitation of the warmest quarter(Bio18),and isothermality(Bio3),respectively.The leading factor affecting holoparasites' distribution was temperature(Bio3).In addition,the distribution of total parasites was similar to that of hemiparasites,and its leading factors were the same as those of hemiparasites.(2)The effects of global warming on the geographical distribution of rare parasitic plants and their hosts(1)There were huge differences in the distributions of high-suitable habitats of the four rare and endangered parasitic plants.The high-suitable habitats of C.songaricum were mainly stable in the central region of Qinghai Province,the central region of Gansu and the southeast of Gansu bordering on Inner Mongolia;B.rossica in the southeast of Jilin and the central-east of Heilongjiang;C.deserticola in the northwest of Xinjiang;while C.mongolica in the southwest of Xinjiang.(2)Global warming will affect the potential distribution of rare and endangered parasitic plants in China.In the lowest greenhouse gas emission scenario(RCP2.6),the suitable habitat areas of C.songaricum may decrease under the joint influence of climate warming and changes of host distribution.However,in the highest greenhouse gas emission scenario(RCP8.5),the suitable habitat areas of C.songaricum are likely to increase because of global warming.In both greenhouse gas emission scenarios,the suitable habitat areas of B.rossica will expand under the joint influence of climate warming and changes of host distribution.In addition,climate change may reduce the suitable habitat areas of C.deserticola,while enlarge those of C.mongolica.The influence of hosts on the distribution of these two Cistanche plants may be fluctuating.(3)It is suggested that special observation sites should be set in the suitable habitat areas of these four parasitic plants,and the core areas for growth should be protected.The conservation of the main hosts of B.rossica should be strengthened,while the tracking and monitoring of other three parasitic plants together with their main hosts are strongly suggested.(3)Host specificity and phylogenetic congruence of Loranthaceae(1)Most genera of Loranthaceae(e.g.Scurrula,Taxillus,and Macrosolen,etc.)had a wide range of hosts without strong host preference.However,at the family level of hosts,the Shannon-Wiener diversity index of Loranthus was only 0.80,which showed a strong preference for hosts from Fagaceae.(2)There was a significant phylogenetic congruence and coevolutionary signal between parasitic genera in Loranthaceae and their host genera(P = 0.005).(3)Phylogenetic asymmetry also existed in this parasite-host interaction network,which can be explained by evolutionary theories related to the "Red Queen hypothesis" or the "Arms race".(4)Closely related parasitic genera tended to parasitize similar hosts.Among the eight genera in Loranthaceae,two closely related genera,Scurrula and Taxillus,had the most similar host composition(Jaccard similarity index = 0.38).