Study On Drought Resistance Of 10 Camellia Osmantha Clones

To clarify the differences in drought resistance between different Camellia osmantha clones and provide a theoretical basis for their rational application in landscaping and greening.In this study,10 clones of C.osmantha（No.1,No.2,No.4,No.63,No.64,No.70,No.73,No.106,No.110 and No.159）were used as research objects.Under the same conditions（control group and drought group）,the effects of drought stress and rehydration test on the growth morphology,physiological biochemical and photosynthetic characteristics of different C.osmantha clones were studied,and combine multiple analysis methods,such as principal component analysis and membership function method,to comprehensively evaluate its drought resistance ability,and a set of drought resistance evaluation systems suitable for C.osmantha has been tentatively formed to improve the efficiency of clone screening and promotion of C.osmantha clones.The main research results are listed below:With the prolongation of drought days and the aggravation of drought stress,the soil water content and relative soil water content continued to decrease,and the time of damage onset and the degree of drought damage differed among clones.The affected leaves of clone 63,with weaker drought resistance,showed the earliest symptoms and the drought damage coefficient was significantly higher than that of the other clones throughout the drought period.After rehydration,it only recovered to level 3 drought damage.Clone64,which has strong drought resistance,showed symptoms of damage later and had a lower drought damage coefficient.After rehydration,it can recover to drought damage level 2.Drought stress had different effects on the growth of C.osmantha clones.Under drought stress,the growth of plant height and ground diameter,biomass and root morphology of each clone decreased significantly,while the root-to-shoot ratio increased and leaf morphology and leaf structure were inhibited to varying degrees.Among them,clone 64,which has strong drought resistance,has a developed root structure and relatively small changes in various indicators,and still maintains good growth under drought stress.（3）Physiological and biochemical indicators of C.osmantha clones showed clear responses to drought stress and rehydration.With the prolongation of drought stress,the relative water content of the leaves of 10 C.osmantha clones all decreased,the total chlorophyll content of clone 4 showed an upward downward trend,while clone 63 showed a gradual downward trend.The total chlorophyll content of the other 8 clones showed a downward trend.The content of malondialdehyde（MDA）and the relative electrical conductivity of the leaves of the 10 clones increased significantly with the increase in the degree of drought.With the intensification of drought,the soluble sugar content of each clone continues to increase;The changes in soluble protein content of clones 63,70,73 and 159 showed an"up down up"trend,while the other 7 clones showed a gradual upward trend.The trend of change in superoxide dismutase（SOD）activity of all clones was"up-down",and the trend of change in peroxidase（POD）and catalase（CAT）activity was generally upward.After 10 days of rehydration,all indicators were alleviated,but there were still significant differences compared to the control group.（4）The net photosynthetic rate（Pn）,transpiration rate（Tr）and stomatal conductance（Gs）of the 10 C.osmantha clones under drought stress showed an overall decreasing trend;the intercellular CO₂concentration（Ci）of clone159 showed a gradually decreasing trend,and the other 9 clones showed a"decreasing-increasing"trend;It also resulted in a decrease in the maximum photochemical efficiency（Fv/Fm）,potential photochemical activity of PSⅡ（Fv/Fo）,maximum photochemical efficiency of PSⅡ（Fv’/Fm’）,actual photochemical quantum efficiency of PSⅡ（ΦPSⅡ）and electron transfer efficiency（ETR）of 10 C.osmantha clones.After rehydration,chlorophyll fluorescence and photosynthetic parameters of each clone increased rapidly,but did not return to pre-drought levels.（5）The drought resistance ability of 10 C.osmantha clones was evaluated by principal component analysis and membership function method,and the strength was as follows:No.64>No.106>No.110>No.73>No.2>No.70>No.1>No.4>No.159>No.63.Through cluster analysis,10 C.osmantha clones could be divided into three groups:drought resistant type,intermediate type and non-drought resistant type.Stepwise regression analysis showed that sponge tissue thickness,Fv/Fm and Fv’/Fm’could be used as important indices to evaluate the drought resistance of the tested C.osmantha clones.