Leaf Growth and Chlorophyll Content of Oilseed Rape (Brassica napus L.) as Influenced by Nitrogen Supply

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Abstract
An experiment was conducted using a greenhouse hydroponics system to investigate the influence of N nutrition on leaf growth and chlorophyll content in oilseed rape (Brassica napus L.) during both vegetative and generative growth. Plants were treated continuously with one of three levels of N supply (30, 100 or 170ppm N). Leaf expansion in terms of lamina area of individual leaves and leaf area per plant, and chlorophyll content of leaves during both growth phases were increased significantly by N supply up to 100 ppm N, which was found to be the optimum level for oilseed rape. N supply of 30 ppm N resulted in N stress while 170 ppm N represents an excessive supply. N supply of 100 ppm N enhanced leaf expansion during H–6 weeks after transplanting by 88–260 % over that of 30 ppm N. Lamina areas of younger leaves responded to N nutrition better than did those of older leaves. Leaf area per plant increased 155–194 % due to increasing N supply but leaf number was increased less remarkably (by 25–44 %). N supply enhanced the contents of leaf chlorophyll a, chlorophyll b, and total chlorophyll but had very little influence on chlorophyll a/b ratios; except that increasing N supply tended to reduce these ratios. Results suggest that variation in leaf chlorophyll content of rape plants in response to N nutrition is a function of leaf age and position. The significance of these results in terms of certain physiological implications for the rape plant is discussed.