| This study takes Maolan karst forest as the research area,and conducts research on a permanent plot of 1 hectare in Maolan,which is a typical area of evergreen and deciduous broad-leaved mixed forest distribution.Natural plant communities in different succession stages are selected as Object,based on the theory of ecological stoichiometry,to study the Ca,Mg,As,Ba,Cd,Cr,Cu,Mn,Ni,Pb,Se,Contents of 13elements in total,Ti and Zn.By comparing the characteristics of plant element content in Maolan karst forests,exploring the correlation between stoichiometric characteristics of plants in various forest layers,and combining correlation analysis,cluster analysis,principal component analysis and other analysis methods,these results can increase the understanding of Maolan.The composition of the karst forest community and the changing laws of elements provide theoretical and data support for the restoration and succession of the forest community,and reveal the stoichiometric characteristics and ecological significance of the Maolan karst forest.The main results are as follows:1.The plant composition surveyed in the sample plot belongs to 37 families,53genera and 60 species,16 species of arbor layer plants,11 families and 14 genera,24species of shrub layer plants,17 families and 22 genera,and 20 species of herb layer.It belongs to 15 families and 19 genera.According to the statistical analysis of the geographical components of the flora,the plants belonging to 37 families in the plot can be divided into 8 types of distribution areas,and the distribution of tropical geographical components is the main type,with 18 families,accounting for 48.65%of the total number of families,and 13 families in the world distribution.,accounting for35.14%,and the distribution of temperate geographical components accounted for16.21%.The distribution types of geographical components belonging to 53 genera are dominated by tropical geographical components,accounting for 54.72%,and 20 genera with temperate geographical components,accounting for 37.74%of the total number of genera.From the perspective of the geographical distribution of families and genera,there are more plants in the tropics,followed by the temperate zone,and the investigated plants are in the transition from tropical to subtropical,which also reflects the vegetation characteristics of the geographical location of Maolan karst forest.2.In the analysis of differences in the distribution of elements in leaves and stem organs of 57 plants in the plot,only the element as in the herb layer has differences between leaves and stems,and in the shrub layer,there are two elements,Mg and Cd,which are different between leaves and stems.In the arbor layer,only Mg elements differ between leaves and stems,so the differences in the distribution of these elements in leaves and stems cannot represent the overall differences in the distribution of elements in leaves and stems.Most elements are not obvious between leaves and stems.Therefore,the stem and leaf organs do not affect the specific element content distribution,so it cannot be considered that there are differences in the distribution of different elements among the leaves and stems of plants in different forest layers.In terms of the expression of element content,the element content of herb layer from high to low is Mn>Ca>Zn>Ti>Ba>Cr>Ni>Cu>Mg>Pb>As>Cd>Se,and the element content of shrub layer from high to low Mn>Ca>Zn>Ti>Ba>Cr>Ni>Cu>Mg>Pb>Cd>As>Se,the element content of the arbor layer from high to low is Mn>Ca>Zn>Ti>Ba>Cr>Cu>Mg>Ni>Pb>As>Cd>Se,in which the content of Se is the lowest among the three forest layer plants,the content of Mn element is the highest among the three forest layer plants,and the major elements Ca and Mg have the highest content.The content gradually increased with the herb layer,shrub layer and tree layer.The average coefficient of variation of the 13 elements is in the order of shrub layer（93.41%）>tree layer（87.59%）>herb layer（83.72%）,and the coefficient of variation of the elements in the three forest layers is very large,which also shows that the differences in the same forest layer are different.The tree species element fluctuates more,and the herb layer fluctuates less than the other two communities.In the analysis of the differences in the content distribution of these 13 elements among the herb layer,shrub layer and tree layer,only Ca（χ~2=3.891,P>0.05）and Mg（χ~2=1.788,P>0.05）were found.There are distribution differences among the three communities,which can reflect the characteristics of karst forest soil rich in calcium and magnesium.3.In the correlation analysis of plant elements,there are a total of 78 element pairs,17 pairs of elements in the herb layer are negatively correlated,61 pairs are positively correlated,of which 13 pairs are significantly positively correlated,accounting for16.67%of the total element pairs;63 pairs of elements were positively correlated,15pairs were negatively correlated,9 pairs of elements were significantly positively correlated,accounting for 11.54%of the total element pairs;8 pairs were negatively correlated in the arbor layer,and the rest were positively correlated,and 12 pairs were positively correlated.Significant positive correlation,accounting for 15.38%of the total element pairs.Based on the correlation analysis of the three communities,the elements As,Pb,Cd and Ti all affect the content of plant elements in the three communities to a large extent,which also reflects that the content of each element in the plant has a certain proportional relationship,and the elements The synergistic or antagonistic effect is more prominent.In the cluster analysis,according to the difference in element content,the leaves of herbaceous plants are clustered into three categories,and the stems of herbaceous plants are clustered into two categories.High,the leaves of the shrub layer plants can be clustered into two categories,and the stems of the shrub layer plants can be clustered into two categories.Among them,the contents of Pb,Cd,Zn,and Ba elements in the leaves and stem organs are higher than other elements.The organs and leaves of the arbor layer are clustered into two categories,and the stems of the arbor layer plants are clustered Into two categories.Comprehensive analysis shows that the content of As,Ti,Ba,and Ni is relatively high.4.Four principal components were determined by principal component analysis,among which As,Pb,Ti,Cd,Cu and Mg were characteristic elements,and the cumulative variance contribution rate reached 63.989%.Plant lineages can be divided into 6 categories.The first category contains 39 species of plants,the second category has 8 species,the third category has 6 species,the fourth and sixth categories have only one plant,and the fifth category has only one plant.The class has 5 plants.In the analysis of element Ca,Mg,As,Cd,Pb content difference and plant phylogenetic relationship,the difference in element content of plants of the same family or genus is small,showing a certain relationship with the phylogenetic relationship.Plants that are closely related often also have the characteristics of small content differences,while the content differences of elements Ca and Mg are small in plants with close kinship in the same family or genus,but the content differences of As,Cd,and Pb are related to the kinship.Relationships tend to be smaller.Combined with the analysis of the five elements,there is no correlation between the relative distance of most plants and the differences in the content of these five elements. |
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