Study On Anotomical Characteristics Of Vegetative Organs And Phenotypic Plasticity Of Rhododendron Species Along An Elevation Gradient In Jiaozi Moutain,Yunnan Province

The global climate changes have influenced ecosystems and human society,and its impact on plant growth and distribution is one of the hot issues of biologists.Alpine is one of the most sensitive areas to climate change.It is an ideal area to study the response of plants to global climate change,because of altitude gradient contains dramatic changes in various environmental factors such as temperature,humidity,light,and terrain.Rhododendron species have a wide distribution range along altitude and latitude,which is an ideal material for studying the adaptability of species along the altitude gradient.Thus,in the present study,we systematic investigate of leaf epidermal morphological characteristics and anatomical characteristics of leaves,petioles,and roots along the altitude gradient of 11 Rhododendron species(such as Rhododendron spinuliferum,R.decorum,R.delavayi,R.rex subsp.rex,R.rubiginosum,R.strigillosum var.monosematum,R.lacteum,R.sikangense var.exquisitum,R.bureavii,R.sphaeroblastum var.wumengense,R.fastigiatum)in Jiaozi Mountain,Yunnan Province.The aim is to explore the adaptation rule of the morphology and anatomical characteristics of the leaf epidermis of Rhododendron to the altitude gradient,and to provide a reference for the study of alpine plants adapting to global climate change.The main research results are:(1)Studies on the leaf epidermis characteristics of 11 species of Rhododendron showed that the leaf epidermal cells were irregular or polygonal in shape.The anticlinal wall pattern of the cells was straight,sinuolate or wavy,and the stomata were all distributed in the lower epidermis and were irregular.The leaf epidermal characteristics of 11 Rhododendron species have interspecies differences with the change of altitude gradient,but the overall change trend is that the stomatal density gradually decreases with the increase of altitude,and the size of stomatal increases with the increase of altitude.(2)Analysis of leaf anatomical structure characteristics showed that the leaves of11 species of Rhododendron were all bifacial leaves.The leaves were composed of cuticle,epidermis,palisade tissue,sponge tissue and vascular tissue.Except for the R.fastigiatum,the other 10 species of Rhododendron have a multiple epidermal structure.The changes of the leaf anatomical traits of 11 species of Rhododendron with the altitude gradient showed that the leaf thickness gradually increased with the increase of altitude,the thickness of cuticle of upper epidermis,palisade/spongy and cell tense ratio decreased firstly and then increased with the elevation.The thickness of cuticle of lower epidermis,spongy ratio increased firstly and then decreased with the elevation,and the vein protuberant degree gradually decreased with the increase of altitude.(3)The arrangement and number of vascular bundles of 11 species of Rhododendron vary greatly.The changes of the petiole anatomical traits of 11 Rhododendron species with the altitude gradient showed that the thickness of the petiole epidermis,petiole cuticle thickness,the thickness of the collenchyma,the thickness of the phloem,the thickness of the cortical,and the diameter of the petiole all increase with the elevation,then decrease.The thickness of the xylem and vascular bundle showed a trend of decreasing gradually with the increasing elevation.(4)The changes of the root anatomical traits of 11 Rhododendron species with the altitude gradient showed that the variation trend of root vascular bundle thickness,conduit density and endodermis thickness increased firstly and then decreased with the increasing elevation.(5)The average phenotypic plasticity index of the characteristics of leaf epidermis,leaves,petioles and roots showed that the plasticity of 11 Rhododendron species from high to low were R.rubiginosum> R.lacteum> R.bureavii> R.sikangense var.exquisitum> R.rex subsp.rex> R.strigillosum var.monosematum >R.delavayi> R.sphaeroblastum var.wumengense> R.decorum> R.spinuliferum> R.fastigiatum.The average plasticity of their anatomical characteristics and leaf epidermal morphological from high to low were root> leaf> petiole> leaf epidermis.