Study On Cold Resistance And Photosynthetic Characteristics Of Osmanthus Fragrans Colour-leaved Group Cultivars

Osmanthus fragrans colour-leaved is a group of cultivars of O.fragrans L whose new shoots or leaves have obvious colour variations.Compared with traditional O.fragrans,it has longer ornamental period and wider use in landscape gardening,so it has broad development prospects.However,due to the limitation of low temperature,the development of O.fragrans colour-leaved cultivars is mainly limited to the Yangtze River Basin and the south area,and there has been no systematic research on the cold resistance of O.fragrans colour-leaved cultivars.and the selection of cold-resistant cultivars and the suitable planting range are still unclear,which also greatly limits the promotion and application of colour-leaved cultivars.As a colour-leaf tree species,O.fragrans colour-leaved cultivars is different from traditional O.fragrans cultivars in leaf pigments.Photosynthetic pigments affect its photosynthesis,and the strength of photosynthetic capacity can reflect the response ability of O.fragrans colour-leaved cultivars to respond to changes of surrounding environment,which has important reference significance in the introduction and cultivation.Therefore,in this paper,the cold resistance and photosynthetic characteristics in different months of different O.fragrans colour-leaved cultivars were studied by using the uniform size of the leaves on the 1a branches of the 4a O.fragrans colour-leaved cultivars cuttages.By measuring and analyzing the dynamic changes of various physiological indexes of detached leaves of 24 O.fragrans colour-leaved cultivars under artificial low temperature stress and the diurnal variations of photosynthetic characteristics,light response curves,photosynthetic pigment content in different months,application of membership function method,cluster analysis,etc.,the comprehensive evaluation of the cold resistance of O.fragrans colour-leaved cultivars was completed.Based on this,excellent O.fragrans colour-leaved cultivars with strong cold resistance and potential for open field cultivation in the north were screened.According to the research results of photosynthetic characteristics,to explore the light management measures of O.fragrans colour-leaved cultivars in Shandong Tai’an area,which provided theoretical support for the large-scale introduction and planting of local O.fragrans colour-leaved cultivars,the selection and breeding of resistant cultivars and the promotion and application.The main results are as follows,1.Through the study on the cold resistance of various O.fragrans colour-leaved cultivars under artificial low temperature stress of different gradients,it can be concluded that:With the decrease of temperature,the change trend of relative conductivity of each cultivars showed an S-shaped curve.By fitting the logistic regression equation,it was concluded that’Aoshuang’,’Dongrong’,’Luocai No.2’and’Mincai No.25’had lower LT₅₀.The change of malondialdehyde content in different cultivars was different,but eventually all show an upward trend,and the change of MDA content showed a negative correlation with the cold resistance ability.The contents of soluble sugar and soluble protein showed a trend of increasing first and then decreasing,but the increasing range and inflection point temperature were different among cultivars.The SOD and POD activities of’Ziyan Princess’showed a trend of continuous decline,and the POD activity of some cultivars showed a trend of"down-up-down-down".The change trend of SOD/POD activity of the other cultivars was roughly divided into two forms:the single peak curve of"up-down"and the double peak curve of"up-down-up-down".（2）There is no significant correlation among the various physiological indexes of cold resistance,and its cold resistance is affected by various physiological factors.So it was necessary to comprehensively analyze the various indexes in order to accurately evaluate the strength of its cold resistance.（3）The results showed that’Aoshuang’,’Dongrong’,’Luocai No.2’and’Mincai No.25’had higher comprehensive evaluation scores by using membership function method,which have great development potential in the promotion of cold-resistant O.fragrans colour-leaved cultivars.2.In June,August and October,the photosynthetic characteristics of’Yongfu Jincai’,’Chaoyang Jinzuan’,’Minnong Guiguan’and’Yongfu Fencai’were measured.The research conclusions are as follows:（1）The diurnal variation curves of net photosynthetic rate of different O.fragrans colour-leaved cultivars showed different variation rules in different months.The results showed that’Yongfu Fencai’was single peak type in June,and the others were double peak type,with obvious midday depression of photosynthesis.In August,the four were double peak type,and in October they were all single peak type.The diurnal variations of transpiration rate and stomatal conductance had a strong positive correlation with the diurnal variations of net photosynthetic rate,while the intercellular CO₂ concentration had a negative correlation with net photosynthetic rate.The decrease of Pn in O.fragrans colour-leaved cultivars is restricted by both stomatal and non-stomatal limitations.The causes of midday depression of photosynthesis include stomatal closure of plants themselves,photoinhibition under strong light,high temperature,drought and other environmental conditions,adverse effects on the ultrastructure and enzymes related to photosynthesis,and accumulation of photosynthetic products,etc.（2）The relationship between photosynthesis and photosynthetic pigment.The photosynthetic pigment content of all cultivars was the highest in August,followed by that in June and the lowest in October.According to the chlorophyll a/b values of the four cultivars in three months,the order of shade-tolerance was’Minnong Guiguan’>’Yongfu Fencai’>’Chaoyang Jinzuan’>’Yongfu Jincai’.During the observation period,the average value of Pn of the four cultivars showed a positive correlation with chlorophyll a,chlorophyll b,total chlorophyll and carotenoid content.The average Pn of’Yongfu Jincai’,’Chaoyang Jinzuan’and’Yongfu Fencai’had a negative correlation with the content of chlorophyll a/b,while that of’Minnong Guiguan’had a positive correlation with the content of chlorophyll a/b.（3）Under different conditions in different months,the light response characteristics of four cultivars were different.’Minnong Guiguan’has the lowest light compensation point and the highest light saturation point during the whole observation period,and has a strong ability to utilize both strong and weak light;the light Ecological amplitude of’Yongfu Jincai’was the narrowest in June and August,and that of’Chaoyang Jinzuan’was the narrowest in October.The light compensation point of the four cultivars ranged from 17 to 65μmol·m^-2·s^-1,and the light saturation point ranged from 893 to 1219μmol·m^-2·s^-1.It can be seen that O.fragrans colour-leaved cultivars is a typical sunny plant,with a wide range of light compensation point and light saturation point,and requires a wide range of light intensity during growth,which can make full use of strong light and weak light to grow.The apparent quantum efficiency of‘Minnong Guiguan’is higher,which indicates that it has a strong ability to use weak light,while the value of‘Yongfu Fen Cai’is smaller,which indicates that it has a poor ability to use weak light.（4）The factors affecting photosynthetic physiology of O.fragrans colour-leaved cultivars.According to the correlation analysis between photosynthetic indexes and influencing factors,it can be concluded that Pn had a extremely significant positive correlation with Tr,a significant positive correlation with Cond,a positive correlation with Ta,PAR and RH,and a negative correlation with Ci;Tr also had a significant positive correlation with Cond,Ta and PAR.The above results show that Pn,Tr and other indicators of O.fragrans colour-leaved cultivars are affected by environmental factors such as PAR,Ta and their own factors,rather than by a single factor.（5）When cultivating O.fragrans colour-leaved cultivars in Tai’an,Shandong,under strong light and high temperature conditions from late spring to summer,appropriate protection should be given from 10:00 to 14:00,such as foliar spray and shading nets;shading is not required in autumn.Measures:When planting O.fragrans colour-leaved cultivars in the garden,it can be planted under sparse tall trees or beside appropriate buildings to meet its demand for light.