Research On The Drought Resistance Of Sedums And Their Landscape Application In Beijing

Given the present situation that there is severe water crisis in the North China with extremely cold winter and hot summer as well as oversimplified usage of landscape plant species, it is reasonably urgent to exert great efforts to select, breed and promote plants species of high ornamental value and strong ability of stress resistence in order to satisfy polytropic circumstances and climates and scientifically restructure landscape application species. Sedum, belonging to perennial flowers, has the advantages of good ornamental value, fairly strong stress resistence and easy propagation, and plays an important role in building the ecological and economical landscape of Beijing. Nevertherless, due to irregular introduction and poor degree of attention, situation of both distribution and application of Sedum is totally unclear in Beijing, not to mention that related systematical and impeccable drought resistence and synthetic evaluation of their landscape application research. Thus, this paper initially investigated on the distribution and application of Sedum resources in Beijing mountainous areas and other city green fields; and then observed their breeding, cultivation and grouth rhythm; finally evaluated their drought resistence and ornamental value. The purpose of this paper is to screen out species of strong drought resistence ability and high ornamental value and then contribute to a better promotion to the Beijing city and even the North China, and give advice to the establishment of ecological and economical city. Main reseach conclusions are as follows.(1) Through investigations of Sedum resources in Beijing, the results showed that 31 sedums clearly named are found, including 13 species and 18 cultivars. However, only S. spectabile、S. lineare、 S. aizoon and S. sarmentosum are frequently applied in the green fields. According to the morphological types and ornamental value, sedums can be classified into 4 categories including foliage, stem, plant-type, flower and fruit ornamental features. The main landscape application of sedums are flower bed and borders, ground covers, roof greenings and potted ornamentals. There are some problems in landscape application, such as unenough exploitation of local resources, weak conservation of introduced species, unitary species and patterns and management issues.(2) Sedums start sprouting and returning green in late February, and generally blanket the ground in May. The flowering phase of the whole colony lasts from middle May to late October; a single species has the flowering duration of above 20 days and its ornamental period is over 200 days. Generally speaking, normal and low height types of Sedum plants fertilize better than high height type, which flowering phase during late spring or in early summer. Both stem length and crown breadth of the high-type grow rapidly before their flowering phase that lasts from early fall to late fall, mainly from April to June, and flowering braches begin to sprout in late July.In late October overwintering buds gradually grow and then leaves begin to fall in November. After sedums have turned yellow and perished, dry strong stems of the high-type will still survive while those of low plants decompose because of being weak and small, and they all live through winter in the shape of overwintering buds.(3) As time of drought stress goes by, leaf water content, cell membrane permeability, free proline and malondialdehyde of fifteen species of Sedum plants increase steadily; in the beginning chlorophyll a/b grows for a period of time but drops in the long run; after 40 days of drought stress, Fv/Fo and Fv/Fm ratios are lower than the Check group. Through correlation analysis of morphological changes, physiology and biochemistry indexes and physiological index of photosynthesis, there is a significant negative correlation between the degree of succulence and driage of detached leaves and water content of plants under drought stress; MDA and driage of leaves have a significant positive correlation; a significant correlation exists between proline, electrical conductivity and other indicators; photosynthetic pigments and chlorophyll fluorescence parameters are significantly correlated. Principle Component Analysis method is utilized to sort those indicators according to their contributions:leaves succulence and proline, chlorophyll a/b and Fv/F0 and the rate of leaf water loss content under drought stress rank at the first class.(4) Fifteen species of Sedum plants are sorted according to their drought resistance using the subordinate function value method as follows:S.’Autumn Joy’> S.’Vera Jameson’> S spectabile ’Brilliant’> S.’Joice Henderson’> S. spectabile’Rosenteller’> S.telephium’Purple Emperor’> S. mexicanum’Gold Mound’> S. hybridum’Immergrunchen’> S. aizoon> S. selskianum’Spirit’> S. spectabile> S. reflexum’Blue Spruce’> S. sexangulare> S. sarmentosum> S. spurium’occineum’.(5) Analytic Hierarchy Process (AHP) method is used to establish the plant landscape comprehensive assessment system based on application potentials and ornamental values including flowers, leaves and other aspects, which aims to build the evaluation hierarchical model of quality and quantity. Analysis results reveal that people always mainly emphasize on ornamental value of leaves of Sedum plants and landscape adaptability followed by flowers and other aspects; S. mexicanum’Gold Mound’, S. reflexum ’Blue Spruce’, S.’Vera Jameson’and S.’Autumn Joy’ etc. with higher synthesis scores can be applied in landscapes in Beijing as well as those with highest single score. Also, some suggestions concerning to the introduction, protection, species selection and application of sedums in Beijing are putforward.