中文摘要：

为从茎秆强度的角度探索套作大豆苗期耐阴抗倒机制,对套作大豆苗期茎秆木质素合成与抗倒性的关系进行了研究。采用耐阴性不同的3个大豆品种（系）,在大豆-玉米套作和大豆单作两种种植模式下,测定茎秆的木质素含量及其合成过程中的苯丙氨酸转氨酶（PAL）、4-香豆酸：Co A连接酶（4CL）、肉桂醇脱氢酶（CAD）、过氧化物酶（POD）等关键酶活性以及茎秆抗折力和抗倒伏指数。结果表明,套作大豆苗期倒伏严重,茎秆抗折力、抗倒伏指数、木质素含量和相关酶活性均显著低于单作。不同大豆品种受套作荫蔽影响程度不同,强耐阴性大豆南豆12茎秆抗折力降低幅度最小,在套作环境下其茎秆抗折力、抗倒伏指数大,茎秆木质素含量高,PAL、4CL、CAD、POD活性强。相关分析表明,套作大豆苗期茎秆木质素含量与抗折力极显著正相关（r=0.890,P〈0.01）,与倒伏率极显著负相关（r=–0.889,P〈0.01）,与4CL、CAD酶活性显著正相关。套作环境下,强耐阴性大豆苗期茎秆中较高的4CL、CAD活性是其维持高木质素含量的酶学基础,而高木质素含量有利于提高茎秆强度,进而增强其抗倒伏能力。

英文摘要：

Stem physical characteristics are closely related to the crop lodging, increasing stem strength is available to resolve the problem of lodging. To explore the effect of intercropping soybean stem strength on the mechanism of shade tolerance and lodging resistance, we studied the relationship between lignin synthesis and lodging resistance. Three soybean cultivars with different shade tolerances were planted in maize–soybean intercropping and soybean monocropping, respectively. The lignin content, activities of phenylalanine ammonia-lyase（PAL）, 4-coumarate：Co A ligase（4CL）, cinnamyl alcohol dehydrogenase（CAD）, peroxidase（POD） which involved in lignin synthesis in stem as well as the snapping resistance and lodging resistance index were determined at seedlings stage. The results showed that the intercropping soybean lodged seriously, the snapping resistance, lodging resistance index, lignin content and activities of the four enzymes were significantly lower than those of monocropping soybean at seedlings stage. The three soybean cultivars were affected differently by intercropping condition, the reduction of snapping resistance of Nandou 12 with strong shade tolerance was the least, its lodging resistance index, lignin content and activities of the four enzymes（PAL, 4CL, CAD, POD） also maintained a relatively high level. The lignin content of intercropping soybean seedling stem was significantly positively correlated with the snapping resistance（r = 0.890, P〈0.01） and the activities of 4CL, CAD, and significantly negatively correlated with the actual lodging percentage（ r = –0.889, P〈0.01）. In a word, the high activities of 4CL and CAD in the soybean stem provide a enzymatic basis to maintain higher lignin content, resulting in higher stem strength and higher lodging resistance in intercropping condition.