| Clerodendron trichotomum has been gradually developed as a excellent new flower shrub because of its excellent ornamental characteristics. It has been used in modern city garden greening. Early landscape investigation showed that, Clerodendron trichotomum was often planted as edge planting or underbush in the existing cultivated community. Insufficient light illumination seriously affected the vegetative growth and the ornamental value. This study was based on the 5-year artificial cultivation tree species of Clerodendron trichotomum to select the high value as the experimental material. 5 test points in different light environments formed from different plant communities were full sunlight, 81% sunlight, 44%sunlight, 19% sunlight and 8% sunlight respectively. There was a comprehensively study on growth index(leaf size, fresh weight, dry weight, specific leaf area, stomatal size, stomatal opening, stomatal density), photosynthetic characteristics(photosynthetic parameters,photosynthetic pigment content), ornamental quality(the number of inflorescence, the diameter of inflorescence, the number of floret, the length of branch, the rate of flowering)and volatile aromatic components to discuss the effects of different light environments on these aspects. By proving the most tolerant shade of Clerodendron trichotomum through researching the impact of insufficient light illumination on the mechanism of light, to determine the most tolerated shade of Clerodendron trichotomum, which contributed to reduce the blindness of the plant configuration and provided reference for the urban landscaping. The results are as follows:1. With the reduction of light intensity, the length of leaf and gradually decreased by8.48%, 5.71%, 4.43%, 0.45% under 81% sunlight, 44% sunlight, 19% sunlight, 8% sunlight compared with the control; the width of leaf decreased by 24.50%, 16.93%, 15.88%, 10.30;The thichness of leaf under different light intensities has no significant difference. Specific leaf area increased by 26.58%, 34.77%, 58.70%, 115.13% under 81% sunlight, 44% sunlight,19% sunlight, 8% sunlight compared with the control. the relative chlorophyll content of Clerodendron trichotomum increased first and then decreased, and under 81% sunlight conditions reached the maximum value. Dry weight/fresh weight decreased significantly with the reduction of light intensity. The stomatal opening in different light conditions compared with the control, with the reduction of light intensity appeared first increased and then decreased, under the 81% sunlight conditions reached the maximum value, the others decreased gradually. Under full exposure and 81% sunlight, the leaf stomatal length ofClerodendron trichotomum had not significant difference, under less than 81% sunlight decreases obviously, the stomatal width compared with the control did not change significantly under different light illumination conditions; There was not significant difference in stomatal density among full sunlight, 81% sunlight and 44% sunlight, but reduced significantly by 39.13% and 54.35% under less than 44% sunlight.2. The net photosynthetic rate, the transpiration rate and the stomatal conductance of Clerodendron trichotomum were highest under full sunlight, and there was no significant difference between the 81% light and the control. The net photosynthetic rate under other conditions decreased by 23.05%, 77.97%, 93.77% with the decrease of light intensity, and the transpiration rate decreased by 26.97%, 32.12%, 43.03%, and the stomatal conductance decreased by 24.68%, 44.98%, 56.39%, and there was a significant difference between the control and the other conditions. However, compared with the control, the concentration of the intercellular CO2 significantly increased by 9.87%, 12.93%, 15.64%, 20.75% with the decrease of light intensity.3. With the decrease of light intensity, the initial stage of floret and initial flowering stage delaying, and the ornamental time was shortened, too. The diameter of inflorescence, the floret number of single inflorescence, the total number of inflorescences and the length of inflorescence were significantly reduced with the decrease of light intensity. However, under81% sunlight, the initial stage of floret, initial flowering stage and the full bloom stage were advanced by 5d, 6d and 9d, the longest time of flowering, the length of inflorescence reaching the maximum of 13.72 cm, and the flowering period was 9 days earlier than the control. Under 19% sunlight and 8% sunlight, the ornamental period was shortened obviously by 7d and 13 d, and the full bloom stage was delayed by 4d and 13 d, the diameter of inflorescence decreased by 21.92% and 24.25%, and the total amount of inflorescence decreased obviously by 32.33% and 59.79%.4. A total of 28 kinds of volatile compounds were identified under the condition of full sunlight from the flowers of Clerodendron trichotomum, which accounted for 96.18% of total relative contents of volatile components, including aromatic hydrocarbons, alcohols,aldehydes, ketones, alkanes, terpenes, esters, other classes etc. Its relatively high content of components were 4-hydroxy-3-methyl aldehyde(32.22%), cis-3-hexenal(11.02%),3-methyl-aldehyde(9.78%), 2-ethyl cyclobutanol(8.06%); a total of 26 kinds of volatile components were detected under 81% light which accounted for 87.63% of total relative contents of volatile components. Its relatively high content of components were 3-methyl aldehyde(31.28%), 2-hexene aldehyde(12.24%), hexanol(8.08%), 2-pentyl-furan(5.42%); atotal of 18 kinds of volatile components were detected under 44% light which accounted for92.97% of total relative contents of volatile components. Its relatively high content of components were 3-methyl aldehyde(46.05%), 2-hexenal(15.58%), alcohol(6.40%),propylaldehyde(5.06%) etc; a total of 18 kinds of volatile components were detected under19% light which accounted for 94.37% of total relative contents of volatile components. Its relatively high content of components were 3-methyl aldehyde(41.96%), 2-(14.73%)2-hexenal, hexanal(11.95%), 1, 5-pentanediol(8.87%) etc; a total of 10 kinds of volatile components were detected under 8% light which accounted for 99.17% of total relative contents of volatile components. Its relatively high content of components were hexanal(64.68%), 2-hexenal(20.02%), alcohol(4.44%), propylene oxide(3.04%) etc.The above results showed that Clerodendron trichotomum tended to light environment,but it could adapt to a wide range of light environmental, possessing certain shade tolerance ability. Under 81% sunlight environment, Clerodendron trichotomum grew well, fragrance of a flower rich, and ornamental quality has been improved; under less than 44% sunlight, the indicators of growth and photosynthetic characteristics of Clerodendron trichotomum were inhibited significantly, the ornamental quality reduced obviously. Consequencely, the study illustrated that appropriate shading was conducive to promote the growth and the ornamental quality of Clerodendron trichotomum, but adverse exceeded a certain degree of shading. |
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