The Diversity, Distribution And Ecology Of Parasitic Angiosperms In China

Parasitic plants are a particular functional species group,which form haustoria obtaining water and nutrients,as well as carbohydrate,partly or wholly from their hosts.They are an important component of vegetation worldwide,influencing ecosystem structure and function.Parasitic plants are widely distributed in various natural and seminatural ecosystems.However,the diversity,distribution and ecology of parasitic angiosperms have seldom studied.China has a tremendous diversity of plant species,but the flora and ecological characteristics of the parasitic angiosperms are not clear.In this study,we compiled the most comprehensive checklist of parasitic angiosperms throughout China.Meanwhile,we analyzed the species diversity,spatial distribution pattern and main influencing factors of parasitic plants in different provinces of China.We explored the host specificity of Loranthaceae among three genera and seven species by using China's digital herbarium to acquire their host species' data in China.In addition,taking Cuscuta japonica as an example,we also analyzed its host range and compared the species diversity of the communities with or without parasitic plants by sample plot method.The primary objective of this study is to characterize the diversity,distribution pattern and host specificity of parasitic angiosperms on a regional scale.Moreover,it can also provide baseline for further understanding of protection,research and utilization of parasitic plants in China.The main research results are as follows:(1)Floristic characteristics of China's parasitic angiosperms(1)According to APG IV,a total of 722 parasitic angiosperms belonging to 12 families and 50 genera were recorded in China.Among them,461 species belonging to 22 genera of six families,were endemic to China.(2)The dominant families and genera of China's parasitic flora were obvious.Three dominant families,namely Orobanchaceae,Loranthaceae and Santalaceae,had 686 species,accounting for 95.01% of the total number of parasitic plants in China.There was one dominant genus,Pedicularis,containing 477 species,accounting for 66.07% of the total number of parasitic plants in China.(3)The geographical composition of China's parasitic flora was diverse,which could be divided into 14 types at the level of genus.28 genera(2~7 groups)were distributed in the tropics,accounting for 57.13% of the total genera while 21 genera distributed in temperate zone(8~14 groups),accounting for 42.84% of the total genera.Therefore,the geographical composition of China's parasitic flora was mainly tropical.(2)Biological characteristics of China's parasitic angiosperms(1)According to Drude life forms,China's parasitic plants could be divided into four categories: herbs,shrubs,subshrubs and vines.Most of the parasitic species belonged to herbs(n = 614,85.04% of the total),followed by shrubs(n=86,11.91%),subshrubs(n=12),and vines(n=10).Among the herbaceous parasites,perennials were the most(n=431),accounting for 70.20% of the number of herbaceous parasites.(2)According to T??itel(2016),China's parasitic plants could be divided into root hemiparasites,root holoparasites,stem parasites and endophytic parasites.Most of the parasitic species belonged to root hemiparasites(n = 560,77.56% of the total),followed by stem parasites(n = 100,13.85%),root holoparasites(n = 61,8.45%),and endophytic parasites(n = 1,0.14%).(3)China's parasitic plants had four types of fruits,namely drupe,nut,berry and capsule.The main fruit type was capsule,accounting for 81.44% of the total species,followed by berry(n=82,11.36%),nut(n=32,4.43%)and drupe(n=20,2.77%).In terms of life forms,the main fruit type was capsules in herbs,with 574 species,accounting for 93.49% of the total number of herbs.In shrubs(n=66)and subshrubs(n=12)were berries while in lianas were drupes(n=8).(3)Geographical distribution pattern and influencing factors of China's parasitic angiosperms(1)We used three species richness values,including absolute species richness(ASR),endemic species richness(ESR),and restrictive species richness(RSR),to reflect the geographical distribution of the parasitic plants in Chinese provinces.The results showed that the absolute species richness was the highest in Yunnan(n=299),followed by Sichuan(n=267)and Tibet(n=205);Henan(n=12)was the lowest.The endemic species richness was the highest in Sichuan(n=205),followed by Yunnan(n=189)and Tibet(n=107);Jiangsu(n=1)was the lowest.Restricted species richness was the highest in Yunnan(n=124),followed by Tibet(n=100),and there was no restricted species richness distribution in some northeastern provinces.In general,the number of parasitic plant species varied largely among provinces,with the highest in the southwest and lowest in the northeast.(2)According to the correlation analysis of species richness(ASR,ESR,and RSR)and main influencing factors(biological and environmental factors),species richness of parasitic plants was positively correlated with seed plant richness(SPR),average elevation(ELE),elevation range shift(ELR),and Isothermality(BIO3)(P<0.05).It was significantly negatively correlated with temperature seasonality(BIO4)and max temperature of warmest month(BIO5)(P<0.05).The results of principal component analysis and stepwise multiple regression analysis showed that elevation factor and heat factor,especially cold season/month temperature,were the main environmental factors influencing the distribution pattern of ASR,ESR and RSR,which separately explained 68.0%,55.20% and 52.6% of the distribution pattern.(4)Host specificity of Loranthaceae in ChinaAccording to generic relationships of Loranthaceae and the number of parasitic plant specimens,the host specificity of different genera of Loranthaceae was studied by selecting Loranthus,Scurrula and Taxillus.The results showed that there was few difference between Loranthus and Scurrula in Shannon-wiener diversity index,but each of the two genera was different from Loranthus.It was suggested that the host specificity could be related to generic relationships of parasitic plants.In order to reveal the host specificity of different species under endemic and nonendemic conditions,seven parasitic species of Taxillus were selected.The results showed that there was no difference in host specificity between endemic and nonendemic species either at the level of family or genus of host plants.Thus,this seems to indicate that the endemism of parasites would not affect their host selection and preference.(5)The impact of C.japonica on local community diversity(1)We set up 30 pairs of field plots(the experimental plots vs control plots)in Lv Shan,Lianyungang(N34°43?21.05?,E119°26?36.17?).The investigation results showed that a total of 37 host plant species belonging to 24 families were recorded in field plots where C.japonica was present.The families of the host plants included Fabaceae,Rosaceae,Liliaceae,Ulmaceae,Moraceae,etc.C.japonica had the highest parasitic rate on Pueraria montana,accounting for 26.77% of the total number of parasitic plants.(2)Parasitic effects could be divided into four levels in light of the coverage of parasites and the growth of the hosts: 0(no effect),?(mild effect),?(moderate effect)and ?(severe effect).The results showed that nearly half of the 69 plant species(n = 32,46.38%)were uninfected(n=28,40.58%).The level ?(mild effect)was the dominant among the infected plant species.(3)Both species richness and Shannon-wiener diversity index of the field plots with C.japonica were significantly higher than that control plots without C.japonica,but Pielou index of the former was lower than the latter and there was no significant difference in Simpson index.The parasitism of C.japonica led to the decrease of the coverage of the dominant species P.montana,which increased the species diversity of local communities.Therefore,the species diversity of China's parasitic angiosperms is rich,and the life form and parasitic type are diverse.In general,the distribution of parasitic plants in 28 provinces is highest in the southwest and lowest in the northeast and the main influencing factors are seed plant richness and elevation range shift in each province.In addition,the distribution of parasitic plants(C.japonica)promotes the diversity of the local plant community.