Effects of nitrogen fertilizer on leaf chlorophyll content and enzyme activity at late growth stages in maize cultivars with contrasting tolerance to low nitrogen
The aim of this study was to investigate the effects of nitrogen (N) fertilizer on the activity of N metabolism and growth of two maize (Zea mays) cultivars with contrasting tolerance to low N.An experiment was laid out in a split-plot design with three replicates.The main plot consisted of two maize cultivars with contrasting tolerance to low N (the low-N tolerant cultivar ZH311 and the low-N sensitive cultivar XY508).The split plot consisted of six N treatments:0,90,180,270,360,and 450 kg/ha.The chlorophyll content and the activities of enzymes involved in N metabolism (NR:nitrate reductase,GS:glutamine synthetase,GDH:glutamate dehydrogenase) at late growth stages were determined,as well as the seed protein content and yield.The results showed that N fertilizer increased chlorophyll content and enzyme activities at late stages,and promoted protein content and yield.As the amount of N fertilizer increased,these indexes increased to a greater extent in XY508 than in ZH311,while all indexes were higher in ZH311 than in YX508.Compared with the low-N sensitive cultivar,the low-N tolerant cultivar retained a higher chlorophyll content and higher activities of enzymes involved in N metabolism,especially at the mid to late grain-filling stage.In addition,the low-N tolerant cultivar required low to mid N levels to improve seed protein content and yield.These results provide information about the physiological mechanisms involved in tolerance to low-N conditions.
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