| With Bt-transgenic hybird cotton variety CCRI29 as material, the study includes two experiments:(l)on effects by applying different level of nitrogen fertilizer (225.0kg · hm-2, high; 112.5kg · hm-2, middle; 0kg · hm-2, low) in the field;(2) on effects caused by changing the ratio of source/sink in cotton. The main results are as follows:The results showed that changing nitrogen application amount had some effects on cotton growth. Compared with mid-nitrogen and low-nitrogen, high-nitrogen boosted the plant height and leaf area index, increased the dissoluble protein content of function leaf on main stem and promoted chlorophyll accumulating in leaf growth anaphase, which extended leaf function period. Photosynthesis of function leaf on main stem, chlorophyll content and dissoluble protein of leaf on reproductive branch under the treatment of mid-nitrogen were higher than those under the other treatments. The dissoluble protein content of leaf was the lowest under the treatment of low-nitrogen, and the chlorophyll content decreased rapidly in leaf growth anaphase, which accelerated the leaf's senescence.Different nitrogen level affected the carbohydrate metabolism in various organs of cotton plant evidently. The carbohydrate synthesis was inhibited under high-nitrogen level, but low-nitrogen level promoted carbohydrate accumulation in leaf on reproductive branch, and dissoluble sugar and starch metabolized in phase, under mid-nitrogen condition. Different nitrogen levels had no significant effect on carbohydrate concentration in seed cotton of bolls before July 15 and bolls from July 15 to Aug. 15. There was significant difference between the lint yields of different nitrogen conditions and caused the order of lint yield was mid-nitrogen > high-nitrogen > low-nitrogen.At the same time, changing nitrogen levels affected SOD activity, POD activity and MDA content of leaf to some extent. The MDA content decreased under mid-nitrogen condition. The changing of SOD and POD activity was various in different growth and development stages, the order of their activity of leaf born around June 1 was mid-nitrogen>hig-nitrogen>low-nitrogen, but the order of leaf activity born around June 22 was high-nitrogen>mid-nitrogen>low-nitrogen.Changing source/sink ratio affected SOD activity, POD activity and MDA content in leaf at the same time. Both increasing and decreasing source/sink ratio could reduce SOD activity and POD activity. The order MDA content of leaf under different treatments was removing leaves>CK>removing buds.Changing source/sink ratio affected the content of dissoluble protein in seed cotton and the corresponding leaf of boll differently under different nitrogen level. The order of dissoluble protein content in corresponding leaf of boll formed before 15 of July (early boll) was: decreasing sink>decreasing source>CK. But dissoluble protein in corresponding leaf of early boll under the condition of decreasing sink was higher than that of the other two treatments significantly.Reducing sink was not favorable to protein accumulation in seed cotton, but increased the starch content, and had less effect on dissolvable sugar content.Removing buds promoted the dry matter weight of boll shell as well as seed cotton weight, thereby increased unit boll weight. But the unit boll weight was decreased after picking off the leaves. Besides, removing leaves and removing buds can heighten the lint percentage.Cotton is an important cash crop, but so far, few studies on the boll and leaf system at the same node were reported, which hindered us for knowing the relationship of source and sink of cotton. In this experiment, the effects on growth and development and physiological characteristics of cotton by changing source/sink ratios under different nitrogen conditions were studied and aimed to provide theoretical basis for cultivation of high yield and physiological breeding. |
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