施氮量对不同肥力水平下夏玉米碳氮代谢及氮素利用率的影响

以郑单958为材料,在高产田和中产田两种地力水平下,利用15N标记法研究了施氮量对夏玉米氮素分配率、利用率和碳氮代谢的影响.结果表明:高产田适量施氮可以提高玉米产量,过量施氮没有表现出进一步增产效果,其氮肥利用率较低(29 04%).中产田随施氮量的增加产量提高,但氮素利用率却降低.各个器官15N积累量依次为籽粒>叶片>茎>根>叶鞘>穗轴.在高产田,当施氮量超过300kg·hm-2时,玉米籽粒和叶片中积累15N有所下降,而茎和根中积累15N的量随施N量的增加而增加;在中产田,随着施N量的增加,籽粒和穗轴积累15N量均相应增加.高产田叶片的硝酸还原酶活性、谷氨酰胺合成酶活性和蔗糖磷酸合成酶活性以及籽粒中蔗糖合成酶活性和酸性转化酶活性均是施氮300kg·hm-2时最大,施氮450 kg·hm-2则抑制了其活性的增强,而中产田的各个酶活性则随着施氮量的增加而增加.

Influence of nitrogen fertilizer rate on carbon-nitrogen metabolism and nitrogen use efficiency of summer maize under high and medium yield levels

The effects of nitrogen fertilizer rate on carbon-nitrogen metabolism and nitrogen use efficiency of summer maize (Zea mays L. cv. Zhengdan 958) were studied by 15N labeling under high and intermediate yield conditions. In the high-yield field, proper nitrogen fertilizer rate increased gain yield, but excessive nitrogen fertilizer rate did not have further yield-increasing effect and nitrogen use efficiency was low (29%). In the medium -yield field, grain yield increased and nitrogen use efficiency decreased with the rise of nitrogen fertilizer rate. The order of 15N accumulation in different organs was: grain, leaf lamina, stem, root, and leaf sheath and spike axis. In the high-yield field, accumulation of 15N in grains and leaves declined, but increased in stems and roots, when nitrogen fertilizer rate was over 300 kg·hm-2. In the medium-yield field, the accumulation of 15N in grains and spike axes increased with the increase of nitrogen fertilizer rate. The highest activities of nitrate reductase, glutamine synthetase, and sucrose phosphorate synthetase in leaves and sucrose synthetase in grains were observed in the high-yield field with a nitrogen fertilizer rate of 300 kg·hm-2. When nitrogen fertilizer rate reached 400 kg·hm-2, there is no further increase in the activities of abovementioned enzymes. However, the activities of these enzymes increased with the increment of nitrogen fertilizer rate in the medium-yield field.