To make clear on the effects of nitrogen (N) application and plant density on lodging resistance and grain yield of winter wheat, we carried out a field experiment with split-plot design using a middle-spike cultivar, Shannong 15, in Tai'an, Shandong province, China in 2008-2009 and 2009-2010 growing seasons. The main plot was N application rate with levels of 180 (Nl) and 240 kg ha"1 (N2), and the subplot was plant density with levels of 1.50 (Dl) and 2.25 million plants per hectare (D2). The lodging-resistance-related traits including morphological characters, chemical components in basal internode, culm lodging resistance index (CLRI), activities of enzymes involved in lignin synthesis, and grain yield were measured in different growth stages. The results showed that the grain yield was decreased with the increase of N rate or plant density, and the largest grain number per spike, 1000-grain weight and grain yield were observed in the NIDI treatment. The culm height of center of gravity and length of basal internode were larger in the Nl or Dl treatment than in the N2 or D2 treatment, whereas, the diameter, thickness, filling degree, and mechanical strength of the basal internode and the CLRI value showed an opposite trend. With the increase of N rate or plant density, the cellulose content, lignin content, C/N ratio of basal internode were decreased but the N content was increased. The interaction between N rate and plant density was significant, which resulted in poor lodging resistance under high N rate plus high plant density. Stepwize regression analysis indicated that N rate had more important effect on lodging resistance than plant density. Therefore, under the experimental condition in this study, the NIDI treatment (180 kg ha"1 of pure N and 1.50 million plants per hectare) is a proper combination of N application and plant density, which may not only improve lodging resistance ofwinter wheat but also obtain high grain yield.%以中穗型小麦品种山农15为材料,在2个氮肥水平(180 kg hm-2和240 kg hm-2)和2个密度(150×104 hm-2和225×104 hm-2)下,研究了抗倒性能相关的形态学特征、茎基部节间化学组分、抗倒指数(茎秆机械强度/茎秆重心高度)、木质素合成相关酶活性和籽粒产量的变化特点,以及抗倒指数与形态学和生化指标的相关性.结果表明,施氮水平和种植密度间存在显著的互作效应,当施氮水平由180 kg hm-2增至240 kg hm-2或种植密度由150×104 hm-2 增加到225×104 hm-2时,茎秆重心高度、基部节间长度显著提高,基部节间直径、厚度、充实度、机械强度和抗倒指数显著降低,同时茎秆基部节间纤维素含量、木质素含量显著减少,含氮量显著升高,碳氮比(C/N比)以及木质素合成相关酶活性显著降低.逐步回归分析表明,氮肥水平对小麦抗倒性的影响大于种植密度.本试验条件下,氮肥水平180 kg hm2和种植密度为150×104 hm-2的处理穗数较低,但穗粒数和千粒重显著高于其他处理,因而籽粒产量最高.建议在降低氮肥用量至180 kg hm-2的同时降低种植密度至150×104 hm-2,可在增强植株抗倒伏能力的同时获得高产.
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