| In view of the stem overgrowth which often occurred in the plug seedlings, this subject studied the overgrowth mechanism of cucumber plug seedlings in different night temperature and same day-night temperature. In addition, DPC and PP333 were used to control the overgrowth. Different concentrations were used in different fertility period in order to improve the quality of the seedlings, increase the yield and provide further theoretical bases and technological guide for popularization of the plug seedlings. The main results were as follows:1. At different night temperature and the same day and night temperature, hypocotyl height was reduced with the declined temperature; 20℃ was most suitable for the growth of hypocotyl thickness. When daytime temperature was same, at lower night temperature, the growth rate of plant height in the daytime was quicker and that of plant height in the night was slower. The dry matter accumulations, root: shoot ratio, G value and robust seedling index at 20℃ were all higher than 13℃and 27℃.The lower temperature reduced the photosynthetic pigment content and nitrate reductase activities in leaves of cucumber seedlings, inversely enhanced the content of the soluble sugar and soluble protein, which were in direct proportion to the changes of temperature. What's more, difference in day and night temperature was beneficial to the accumulation of organic matter and2. enhances the adaptability of the plant to the unfavorable environment. From the effect of different temperatures on the absorption of macro elements on cucumber seedlings, we can conclude that N content in the root and shoot, P content in plant and K content in leaves increased with lowering of temperature. However, lower temperature decreased N content in leaves and K content in roots and shoots.3. GA, IAA, ABA content in roots and leaves and IAA, ZR content in shoot increased with the lowering of temperature, ZR content in roots decreased inversely. GA content in shoot was higher at high night temperature, which promoted the elongation of shoot; ABA content in shoot and ZR content in leaves were low at first and higher than two other treatments a few days later at low night temperature. Outstanding increase of ABA content induced by lower temperature inhibited the vegetable growth of cucumber seedlings, which caused the inadequate supply in later period and influenced the improvement of seedlings quality. 4. When day temperature was steady, the quality of cucumber seedlings was highest at about 20℃ in the night. 20℃~27℃ was beneficial to grow robust seedlings at same temperature in the day and night. Difference between day and night temperatures was helpful to accumulation of dry matter and production of photosynthesis and enhances the adaptability to the environment.Compared with CK, with the treatment of DPC and PP333 on the surface of the substrate and in the cotyledon period, plant height was reduced and stem diameter was enhanced; dry matter accumulation, root: shoot ratio, G value and robust seedling index increased and content of water was reduced; photosynthetic pigment content and photosynthetic parameters in leaves were enhanced, indicating that DPC and PP333 had good effect on seedling quality. With the treatment of DPC and PP333 in two different periods, macro elements content in plant were enhanced in varying degrees. N,P,K contents increased5. with the DPC concentration enhancement; N content in roots and shoots, P content in root with PP333 treatment on the surface of substrate and N content in leaves and K content in root were highest at 20mg/L with treatment in the cotyledon period. 6. Contents of the soluble sugar, soluble protein(Pr) and praline(Pro) were higher remarkably than CK, and content increase was in direct proportion to the concentration of DPC and PP333,which was beneficial to enhancing the resistance of cucumber seedlings to adverse environment. Compared with CK, in different treatment SOD activities were reduced, POD activities were enhanced strik... |
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