| The Leymus chinensis alliance is a peculiar type in the eastern Eurasian steppe.The total area of the L.chinensis community in the world is 420,000 square kilometers,about half of which are distributed in China.It is one of the most widely distributed communities in the grassland zone in China and is also the vegetation type with the highest economic value.The L.chinensis alliance has different community types.A comprehensive and in-depth research on the geographical distribution,community characteristics and productivity of L.chinensis communities is of important guidance for grassland ecosystem management,grassland restoration and establishment,and can also provide basic data for vegetation regionalization and compilation of flora in China.Here,we investigated a total of 189 sample sites of L.chinensis community through field investigations,and comprehensivly analyzed their distribution,community species composition characteristics,biodiversity,and community types based on environmental factors.And on this basis,the changes and influencing factors of individual,population and community biomass of L.chinensis were systematically analyzed.The main conclusions are as follows:1.1Floristic characteristics of L.chinensis community1.In 189 sample sites,388 species of vascular plants(the subspecies is included)were recorded,belonging to 46 families and 190 genera The family containing the most species was Asteraceae,followed by Poaceae and Fabaceae.The three major families accounted for 42.78%of the total species.2.The life form of the species in L.chinensis community was dominated by perennial herbs,accounting for 73.26%of the total species,and the second was the annual and biennial herbs,accounting for 18.75%of the total species.The proportions of shrubs and semi-shrubs were very small,which were 3.09%and 2.58%respectively.The Raunkiaer life form was dominated by hemicryptophyte accounting for 61.86%of the total species.The second was annual plants,accounting for 18.04%.Additionally,geocryptophyte accounted for 14.69%and there were few phaenerophyte and chamaephyte.3.The species water ecological type spectrum of L.chinensis community was dominated by Xerophytes,accounted for 42.78%of the total species.Mesophytes took the second place and accounting for 54.38%of the total species,of which annual mesophytes accounted for 18.04%.Hygrophyteswere the least,accounting for 2.84%of the total species.4.The geographic composition of L.chinensis community was mainly composed of temeperate element,accounting for 70.10%of the total species.The second was the East Asia element,accounting for 15.21%of the total species.The Tethys element accounted for only 3.09%.5.The species with the highest existence in the L.chinensis community is L.chinensis,with an occurrence frequency of 100%.The second is Cleistogenes squarrosa,with an occurrence frequency of 71.12%.Among all the species,the species with the existence degree of grade I was the most,accounting for 92.4%of the total species.1.2 Community characteristics of L.chinensis community1.L chinensis is mainly distributed in the eastern part of the Eurasian steppe and is a Dauri-Mongolian species.Among the samples extracted from the GBIF database,the distribution location of France,Xinjiang,and Tibet was doubtful.2.The 189 L.chinensis sample sites investigated were distributed in Heilongjiang,Jilin,Hebei,Inner Mongolia,Shanxi,Shaanxi and Gansu provinces.Among them,Inner Mongolia had the largest number of sample sites and sample plots,while Shaanxi and Gansu provinces only had sporadic distribution.3.L.chinensis community was divided into three vegetation types,including L.chinensis typical steppe,L.chinensis meadow steppe and L.chinensis meadow.According to the classification of community dominant species,L.chinensis community can be divided into 8 association groups and 89 associations in the L.chinensis typical steppe;5 association groups and 20 associations in the L.chinensis meadow steppe;and 5 association groups and 16 associations in the L.chinensis meadow.4.The nature of the Leymus chinensis community belongs to the nature of the steppe.1.3 Species diversity of L.chinensis community1.The species richness,Shannon Wiener index,Simpson index and Pielou evenness index of L.chinensis meadow steppe were all the highest,and the diversity indexes of the three types were significantly different.There was no consistent trend in the relationship between different types of species diversity and environmental factors.2.The jaccard index based on binary data and the bray-curtis index based on quantitative data in L.chinensis community showed significant correlations with geographical distance and climate difference.1.4 Phylogenetic diversity and community construction of L.chinensis community1.For the whole L.chinensis community,the phylogenetic structure of typical steppe and meadow was dominated by aggregation,indicating that the phylogenetic structure of the community was mainly driven by environmental filtration.The phylogenetic structure of meadow steppe was mainly divergence,and interspecies competition was the main influence factor2.The?-diversity of the phylogeny of L.chinensis community was jointly driven by environmental filtration and diffusion restrictions.Among them,the spatial turnover of species played a leading role.1.5 Aboveground biomass of L.chinensis individual1.Across large scale,the aboveground biomass of L.chinensis individuals was mainly driven by biotic factors(plant traits),while environmental factors indirectly affected the aboveground biomass of individual L.chinensis.2.Plant height(PH)and stem diameter(SD)were the best predictors of the aboveground biomass of L.chinensis individual in large-scale or local scale.3.An unified equation for estimating the aboveground biomass of L.chinensis individual was established:AGB=-0.638+0.405*SD+0.017*PH1.6 Aboveground biomass of L.chinensis populations and communities1.The average aboveground biomass of L.chinensis community was160.9±71.18 g/m~2,and the average species richness was 24±9 species/site.The aboveground biomass and species richness of L.chinensis typical steppe were the lowest with the aboveground biomass being 139.2±59.96 g/m~2,and species richness being 21±6.35 species/site.2.The average proportion of aboveground biomass of L.chinensis population relative to that of whole community was 56.48±19.37%,with the highest percentage being 80.00±12.84%in the meadow,and the lowest percentage being 39.76±16.38%in the meadow steppe.3.Across large scale,the aboveground biomass of L.chinensis population was significantly and positively correlated with the coverage,mean annual precipitation,mean annual temperature,precipitation of coldest quarter and min temperature of coldest month,and significantly and negatively correlated with the species richness,species evenness,and altitude.At the local scale,the aboveground biomass of L.chinensis population in the typical steppe was significantly and positively correlated with the coverage,the mean annual precipitation,slope,precipitation of coldest quarter and min temperature of coldest month,and significantly negatively correlated with the species evenness and species richness.Additionally,the aboveground biomass of L.chinensis population in the meadow steppe was negatively correlated with the species evenness and species richness,while the aboveground biomass of L.chinensis population in the meadow was significantly and positively correlated with the mean annual precipitation,the mean annual temperature,slope and min temperature of coldest month,and significantly negatively correlated with the species evenness.4.Across large scale,the aboveground biomass of the L.chinensis communities was significantly positively correlated with the coverage,the mean annual precipitation,slope and precipitation of coldest quarter,and significantly negatively correlated with the altitude and species evenness.At the local scale,the aboveground biomass of typical steppe was significantly and positively correlated with the coverage,the mean annual precipitation,slope and precipitation of coldest quarter,while the aboveground biomass of meadow steppe was significantly positively correlated with the slope,but was significantly negatively correlated with the species richness and species evenness.Additionally,the aboveground biomass of meadow was significantly positively correlated with the mean annual precipitation,the mean annual temperature,slope and precipitation of coldest quarter and min temperature of coldest month.5.The driving mechanism of aboveground biomass of L.chinensis community was dominated by the niche complementation effect in typical steppe and meadow,but dominated by the selection effect in the meadow steppe. |
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