Abstract: The activities of key enzymes related to nitrogen metabolism in functional leaves of rice at low nitrogen level (125 kg/hm2) and normal nitrogen level (250 kg/hm2) were studied under ambient air and elevated CO₂ concentration(Ambient+200 μmol/mol) conditions at different developmental stages by Free Air Carbon-dioxide Enrichment (FACE) approach. Compared with the ambient conditions,the activities of nitrate reductase (NR) and protease increased under elevated CO₂ concentration conditions at both the normal and the low nitrogen levels and the change extent of the activities of the two enzymes was larger at the normal nitrogen level than that at the low nitrogen level.NADH-glutamate dehydrogenase (NADH-GDH)and glutamine synthetase (GS) activities decreased at the low nitrogen level,whereas the decline trend was somewhat alleviated at the normal nitrogen level.Therefore,elevated CO₂ concentration accelerated the transformation of NO₃^-to NH₄⁺ but inhibited the assimilation of NH4+ to organic N and improved protein degradation after flowering,which might accelerate the decrease of nitrogen content in rice leaves and it was the inner factor that induced the decrease of nitrogen content in rice leaves.Nitrogen application increased the activities of enzymes related to nitrogen assimilation metabolism,decreased the activity of protease and so mitigated the decrease of nitrogen content in rice leaves.

Key words: free air carbon dioxide enrichment, rice, nitrogen metabolism, functional leaf, enzyme activity

摘要： 利用FACE（Free Air CarbonDioxide Enrichment）平台技术，研究了低氮（125 kg/hm2，以纯N计）和常氮（250 kg/hm2）水平下，高浓度CO2（周围大气CO2浓度+200 μmol/mol）对水稻不同生育期功能叶N代谢关键酶活性的影响。结果表明，高浓度CO2提高了叶片硝酸还原酶和蛋白水解酶的活性，两者在常N下的响应程度大于在低N下的响应程度；高浓度CO2降低了低N下叶片谷氨酰胺合成酶和谷氨酸脱氢酶（NADHGDH）活性，常N水平下酶活性的下降趋势得到改变或缓解。由此可见，高浓度CO2条件下NO3-转化为NH4+加速，而NH4+进一步同化为有机N却受阻，而且，由于后期蛋白水解加速，将进一步加剧叶片N含量的下降。这是水稻叶片N含量下降的内在因素。而增施N肥，有利于同化酶的表达，降低叶片蛋白水解酶活力，从而缓解叶片N含量的下降。

关键词: 大气二氧化碳浓度升高, 水稻, 氮代谢, 功能叶, 酶活性