| Excessive application of nitrogen has been an important limiting factor which influences sustainable development of greenhouse vegetable in China. In order to solve this problem, on the one hand, screening cultivars with high nitrogen use efficiency followed by genotypic difference; on the other hand, developing reasonable cultivation mode to reduce the excessive application of nitrogen. Cucumber(Cucumis sativaus L.) is one of the most important vegetable that is cultivated in unheated greenhouses worldwide. It was confirmed that grafting can improve chilling-resistance, disease-resistance, and salt-tolerance of cucumber. However, it is unknown that whether grafting can increase nitrogen use efficiency or not. In order to obtain rootstocks with high nitrogen use efficiency, some rootstocks with different nitrogen use efficiency were screened and evaluated in this paper. On this basis, the response of different grafting combinations to nitrogen stress was discussed and the mechanism of nitrogen absorption and utilization of rootstock to cucumber was investigated. The results are as follows.1. The difference of nitrogen use efficiency among 16 rootstocks was studied in hydroponics experiment by analyzing the growth, the total nitrogen content and the nitrogen accumulation at seedling stage under 0.5 mM and 14 mM nitrate levels. The results showed that:the variation coefficient of the relative dry mass, the relative nitrogen accumulation, and the total nitrogen content were 0.20,0.24 and 0.17, respectively. The relative dry mass and the relative nitrogen accumulation are considered as the index of' high nitrogen utilization. The rootstock was divided to three types:high nitrogen efficiency, medium nitrogen efficiency and low nitrogen efficiency. Cultivar of figleaf gourd(Cucurbita ficifolia Bouche) has high nitrogen use efficiency,5 rootstocks such as Qiandao No.1 and Genwangda pumpkin and have medium nitrogen use efficiency,4 rootstocks such as Daban pumpkin have low nitrogen use efficiency. The growth inhibition of cucumber of Jinyou No.l and Jinchun No.2 was compared. The results showed that the relative root weight of JinYou No.1 was increased by 139% more than Jinchun No.2 and the relative root length of Jinyou No.l was increased by 36.6% more than Jinchun No.2. The NR activity of Jinyou No.1 was significantly higher than Jinchun No.2. The growth inhibition of Jinchun No.2 is more apparent under N stress.2.'Jinchun No.2'(Cs), a relative nitrogen-sensitive cucumber cultivar, figleaf gourd (Cm), a relative high nitrogen use efficiency pumpkin cultivar, were reciprocal grafting. The growth and the nitrogen use efficiency of different grafting combination (Cs/Cm, Cs/Cs, Cs, Cm/Cs, Cm/Cm, Cm) was investigated. The results showed that the relative content of dry weight of Cs/Cm is increased by 45% and 21% more than Cs/Cs and Cs, the relative content of soluble protein is increased by 29.4% and 20.1% and the relative content of amino acids is increased by 1-fold and 2.6-fold, respectively. The shoot NR and GS activity of Cs/Cm is increased by 74.2% and 76.5%,24.3% and 22.1% more than Cs/Cs and Cs, respectively. The nitrogen utilization and the relative nitrogen accumulation of Cs/Cm are significant higher than Cs/Cs and Cs. The nitrate content, the soluble protein and the amino acids of the rootstock root of Jinchun No.2 is significant lower than the root of figleaf gourd at the low N level, either of the NR and GS activity. The shoot nitrogen compounds content and NR, GS activity of figleaf gourd have no significance under the different nitrogen levels. The above results indicate that C. ficifolia, as an excellent rootstock, can significantly promote growth and improve the nitrogen absorption and utilization efficiency. |
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