稗草阴蔽对大豆根瘤固氮速率的影响

 在自控人工气候室内系统研究了稗草阴蔽对大豆根瘤固氮速率的影响。结果表明，在每盆6、12和24株稗草的阴蔽作用下，播后44—101天期间大豆单株根瘤的平均固氮速率分别比无阴蔽对照下降了31.5、39.5和44.5%。稗草阴蔽引起大豆根瘤固氮速率下降的原因与其通过降低大豆植株的受光量及其叶片的CO2传导速率从而降低其叶片的净光合速率有关。播后43一75天期间在每盆6、12和24株稗草的阴蔽作用下，由于大豆植株的受光量分别比无阴蔽对照平均减少了32.1，39.1和43.4%，叶片的CO2传导速率分别比无阴蔽对照平均下降了14.0，16.7和19.3%，导致大豆叶片的净光合速率分别比无阴蔽对照降低了25.4，32.7和37.3%。

EFFECT OF BARNYARDGRASS(ECHINOCHLOA CRUSGALLI) SHADING ON NITROGEN FIXATION OF SOYBEANS

Experiments were conducted in a automaticaly controled climat chamber to study the effect of barnyardgrass shading on soybean nitrogen fixation. Root interference between barnyardgrass and soybean was eliminated by seeding the crop in small pots which were put in big pots and the weed between the small and big pots. The results showed that barnyardgrass at density of 6,12, and 24 plants/pot significantly reduced the light intensity over soybean plants averagely by 32.1, 39.1 and 43.4% leaf CO_2 conductance by 14.0, 16.7 and 19.3%, leaf net phytosynthetic rate by 25.4, 32.7 and 37.3% during the growth season between 43 and 75 days after planting, and resulted in a marked decrease in N_2-fixing rate per soybean plant by 31.5, 39.5 and 44.5%, respectively.