Anatomical Structure And Eco-physiological Characteristics Of Firmiana Dansiaensis Huse Et H.S.kiu

Firmiana dansiaensis Huse et H.S.Kiu is a second-class key protected wild plant in China,which was originally recorded in Danxia landform.Its new population was recently found in limestone mountain area,but it is still endemic to Guangdong.In this study,F.dansiaensis from two main distribution areas of Danxia landform（Nanxiong Cangshizhai and Renhua Danxia Mountain）in Guangdong were taken as the research object,the structure of roots,stems and leaves were dissected and their ecological adaptability characteristics were discussed.the physiological and ecological indexes such as leaf photosynthetic rate were determined,and the contents of some elements and stable carbon and nitrogen isotopes in soil and rock samples of plant vegetative organs and their habitats were analyzed.The potential suitable growth area of F.dansiaensis was predicted,which provides a theoretical basis for better protection of F.dansiaensis.The main conclusions are as follows:（1）There are thick periderm,dense ducts and secretory cavities in the secondary structure of F.dansiaensis root and stem,which is beneficial to F.dansiaensis to resist drought.The developed secretory cavity secretes a large amount of mucus,diluting the concentration of salt in the cells,making F.dansiaensis from the toxicity of Danxia landform strong acidic soil,and strengthening the ability of drought resistance and water conservation of plants.The thickening of the epidermal cells on the leaves protected the mesophyll cells from the high temperature in summer,and there was a secondary vascular bundle in the main vein of the leaves,which greatly improved the water transport efficiency of the plant.（2）The diurnal variation characteristics of leaf photosynthetic characteristics were compared.the results showed that the air temperature,atmospheric relative humidity,photosynthetic active radiation,net photosynthetic rate,transpiration rate,stomatal conductance,CO₂ concentration and leaf SPAD value in summer were higher than those in autumn,but the water use efficiency and the correlation among factors in summer were lower than those in autumn.It can be seen that F.dansiaensis shows a high adaptability to the high temperature and humidity environment of Danxia landform with high net photosynthetic rate,transpiration rate and stomatal conductance in summer.（3）Among the 8 elements tested,there was no significant difference among the corresponding elements in F.dansiaensis plants of Cangshizhai in Nanxiong and Danxia Mountain in Renhua,indicating that the growth of F.dansiaensis may be less affected by the rhizosphere environment.The law of migration and accumulation of the four elements shows that there is no obvious"rock-soil-plant"migration process in the source of elements in F.dansiaensis,and the law of absorption and accumulation of elements is relatively complex.The law of Cd migration and accumulation suggests that there may be different degrees of Cd pollution in Nanxiong Cangshizhai and Renhua Danxia Mountain in Guangdong,among which the Cd pollution in Renhua Danxia Mountain is higher.（4）There was no significant difference inδ¹³C values between Nanxiong Cangshizhai and Renhua Danxia Mountain in Guangdong,but the linear correlation study showed that there was no correlation between plantδ¹³C and its rhizosphere environment.As for theδ¹⁵N value,there was an obvious difference between the two environments,which indicated that the soil condition of Danxia Mountain in Renhua was better than that in Cangshizhai,Nanxiong,and the content ofδ¹⁵N in F.dansiaensis root of Danxia Mountain in Renhua was higher,and there was no significant correlation between soil and plants.（5）According to the longitude and latitude information of F.dansiaensis distribution point obtained from field investigation and literature data,the potential suitable growth area of F.dansiaensis was predicted in Maxent model.It is found that the potential suitable area is mainly concentrated in the south of China,especially in the north-central mountain area of Guangdong.The range of the high suitable growth area is mainly limited by the Nanling Mountains,and the mountain area to the south of the Nanling Mountains is the high incidence zone of the potential suitable growth area of F.dansiaensis.The contribution rate of climatic environmental variables shows that the main environmental factors affecting the distribution of F.dansiaensis are solar radiation and atmospheric water vapor pressure.