LAUSR

BACKGROUND Nitrogen (N) is the key nutrient required for high cotton production, however, its excessive use can increase the cost of production and environmental problems. Reducing the application of N while sustaining the yield is an important issue to be solved. Therefore, the current study was designed to investigate the genotypic variations in subtending leaf physiology and its contribution to seed cotton yield of contrasting N-efficient cotton genotypes under various N levels in pot and field conditions. RESULTS The results showed that the application of N increased the enzymatic activities related to carbon (C) and N metabolisms. Under the same N level, the C/N metabolisms of the N-efficient genotypes were significantly higher than N-inefficient genotypes, indicating a strong N assimilation and photo-assimilation ability in N-efficient genotypes, especially under low N level. Moreover, the antioxidant enzymatic activities were significantly higher, while malondialdehyde content was lower in N-efficient cotton genotypes than in N-inefficient ones. Therefore, N-efficient cotton genotypes showed strong resistance, higher C/N metabolisms, and provided sufficient dry matter for boll development. As a result, the yield, N use efficiency, and value cost ratio of the N-efficient cotton genotypes were higher than the N-inefficient genotypes. CONCLUSION It was confirmed that the higher C/N metabolisms in the cotton subtending leaves of N-efficient cotton genotypes could support higher seed cotton yield under relatively low N application. This article is protected by copyright. All rights reserved.