Leaf Anatomical Characteristics And Environmental Adaptability Of Sorbus Species

The genus Sorbus L.(Rosaceae,Maloideae)is one of the genera with the most complicated taxonomic problems in Rosaceae.In this paper,19 species and 2 varieties of Sorbus were studied.Leaf anatomical characteristics of 21 Sorbus taxa were observed and compared by paraffin section method,the commonality and interspecific differences of leaf anatomical traits were analyzed.Based on the plasticity of leaf anatomical characteristics and the relationship between leaf anatomical structure and environmental factors,the environmental adaptation strategies of leaf anatomical structure of Sorbus were discussed.It is expecred to provide a new scientific basis for the systematic classification,introduction technology and domestication of Sorbus species.The main research results are as follows:1.Leaf anatomical structure characteristics.Leaves of Sorbus species are all of typical dorsal-ventral pattern,12 leaf anatomical structure indices(leaf thickness,upper epidermis thickness,upper cuticle thickness,lower epidermis thickness,lower cuticle thickness,palisade parenchyma thickness,spongy parenchyma thickness,the ratio of palisade parenchyma to spongy parenchyma in thickness,cell tense ratio,sponge ratio,diameter of midrib and midrib protuberant degree)showed significant interspecific differences(p<0.01),which are representative evaluation indices.Leaf thickness ranges from 96.5(S.helenae)to 285.75 ?m(S.folgneri).Upper epidermis thickness were greater than lower epidermis thickness,and upper cuticle thickness were also greater than lower cuticle thickness.Stomata are distributed in the lower epidermis and stomatal apparatus do not sag.Papillae were observed in the lower epidermis of four pinnate-leaved species(S.aestivalis,S.hupehensis,S.sargentiana and S.scalaris).Palisade parenchyma were composed of 1?3 layers of cells,the thickness ranges from 36.24(S.megalocarpa)to 126.29?m(S.prattii).Spongy parenchyma thickness ranges from 32.77(S.folgneri)to 122.44 ?m(S.helenae),with obvious intercellular spaces.Ratio of palisade parenchyma to spongy parenchyma in thickness(P/S)ranges from 0.56(S.meliosmifolia)to 1.93(S.aestivalis).Cell tense ratio ranges from 26.57%(S.meliosmifolia)to 50.03%(S.coronata var.glabrescens).Sponge ratio ranges from 28.61%(S.sargentiana)to 49.03%(S.meliosmifolia).The vascular bundles of the midrib are heart-shaped or nearly heart-shaped,which are typical collateral vascular bundle.The diameter of midrib ranges from 267.87(S.aestivalis)to 1193.63 ?m(S.keissleri),the midrib protuberant degree is highest in S.megalocarpa(10.73),and smallest in S.prattii(1.4).Varying degrees of correlation among leaf anatomical structure indices,reflecting the synergistic changes between leaf veins and the transport and assimilation tissues of leaves.High correlation among the six indices(|r|>0.8,p?0.01).A significant positive correlation among leaf thickness,palisade tissue thickness and spongy tissue thickness;a significant positive correlation between P/S and cell tense ratio,while a negative correlation between P/S and sponge ratio.Lower cuticle thickness and the diameter of midrib are independent,only have positive correlation with upper cuticle thickness and the midrib protuberant degree,respectively.2.Interspecific differences in leaf anatomical structure.Principal component analysis showed that the six indices(P/S,leaf thickness,spongy parenchyma thickness,sponge ratio,cell tense ratio and palisade parenchyma thickness)had significant interspecific differences among 21 taxa(contribution value>0.8),which are important leaf anatomical structure indices to distinguish the genus Sorbus.Cluster analysis is a comprehensive evaluation of the similarity of leaf anatomical traits in Sorbus taxa.Dendrogram showed that 19 species and 2 varieties were divided into five clades at the Euclidean distance of 10,which indicated that the leaf anatomical structure of Sorbus was affected by interspecific differences and environmental adaptability.3.Plasticity of leaf anatomical structure of Sorbus species.Plasticity index of leaf anatomical structure indices ranged from 0.02 to 0.95,with a large variation.Upper and lower cuticle thickness,upper and lower epidermis thickness showed greater comprehensive plasticity.Epidermis structure is the primary structure for maintaining the leaf functional stability in the heterogeneous environment.Plasticity index of diameter of midrib is the smallest,its regulation ability may be relatively weak in the face of environmental pressure.Leaf anatomical structure of S.folgneri(FJS)has the greatest comprehensive plasticity,which enables it to adapt to more diverse habitats.However,the comprehensive plasticity of leaf anatomical structure of S.megalocarpa(LCG)is the least,indicating that the potential adaptability of this species is relatively weak in the current environment.4.Relationship between leaf anatomical structure of Sorbus species and environment.Correlation between 12 anatomical indices and 18 environmental factors showed that each index changed with the change of latitude,longitude,altitude,climatic factors and soil conditions.Among the geographical factors,altitude had a higher correlation with leaf anatomical structure.Five indices(leaf thickness,upper epidermis thickness,palisade parenchyma thickness,spongy parenchyma thickness and cell tense ratio)were positively correlated with altitude,while diameter of midrib and midrib protuberant degree were negatively correlated with altitude.Among the climatic factors,precipitation seasonality(Bio15)was highly correlated with leaf anatomical structure.Three indices(leaf thickness,lower epidermis thickness and spongy parenchyma thickness)were positively correlated with precipitation seasonality,while other three indices(upper cuticle thickness,diameter of midrib and midrib protuberant degree)were negatively correlated with precipitation seasonality.Among the soil factors,topsoil sand fraction(T?SAND)and subsoil texture(S?USDA?TEX)were the dominant factors affecting leaf structure.Diameter of midrib and midrib protuberant degree were positively correlated with topsoil sand fraction and subsoil texture,while three indices(leaf thickness,palisade parenchyma thickness and spongy parenchyma thickness)were negatively correlated with topsoil sand fraction and subsoil texture.In this study,there were significant differences in leaf anatomical characteristics among Sorbus species,which provided a certain reference in the interspecific classification,but the support for the existing taxonomic section were not high.Twelve indices showed synergistic relationship,which is an evolutionary adaptation strategy of leaf anatomical structure in Sorbus.Variation rules of each structural index and environmental factors are different,which shows that different leaf structures have obvious differences in the requirements of environmental conditions.In the long-term evolutionary process,leaf anatomical structure of species distributed in different environments may form their own evolutionary rules,and further demonstrates the diversity of Sorbus species in environmental adaptation strategies.