Abstract: Using Taraxacum mongolicum， Bidens pilosa， and Ageratina adenophora as materials and （NH₄）₂SO₄ and KNO₃ as nitrogen sources， four nitrogen treatments were set up for nitrogen deposition simulation experiments： control （0 g·m^-2·a^-1）， low nitrogen （2 g·m^-2·a^-1）， medium nitrogen （6 g·m^-2·a^-1）， and high nitrogen （12 g·m^-2·a^-1）. The seed germination， seedling growth， and physiological indexes of the three species of Asteraceae weeds were measured to explore the response patterns to nitrogen deposition. The results showed that： The germination indexes of T. mongolicum and B. pilosa increased and then decreased with the increase of nitrogen concentration， while the germination energy and Timson’s Index of A. adenophora gradually declined. The nitrogen concentration of 2 and 6 g·m^-2·a^-1 promoted the indexes of T. mongolicum， B. pilosa and A. adenophora， such as plant height， root length， and dry weight. However， these indicators were inhibited under the concentration of 12 g·m^-2·a^-1. The intercellular CO₂ concentration （C_i） of T. mongolicum， B. pilosa and A. adenophora showed a decreasing and then increasing trend with the increase of nitrogen concentration， while chlorophyll content exhibited an opposite trend. The net photosynthetic rate （P_n） of T. mongolicum and B. pilosa showed a “ promotion at low levels and suppression at high lebels” with increased nitrogen concentration， while the P_n of A. adenophora was continuously suppressed at all nitrogen levels. These indicated that medium and low levels of nitrogen deposition could enhance the emergence and growth of Asteraceae weeds and help them expand their populations， while high levels of nitrogen deposition might limit their propagation and dispersal.

Key words: Nitrogen deposition, Asteraceae weed, Seed germination, Seedling growth, Photosynthetic characteristics

摘要： 本研究以蒲公英（Taraxacum mongolicum）、鬼针草（Bidens pilosa）和紫茎泽兰（Ageratina adenophora）为材料，以（NH₄）₂SO₄和KNO₃为氮源，设置对照（0 g·m^-2·a^-1）、低氮（2 g·m^-2·a^-1）、中氮（6 g·m^-2·a^-1）、高氮（12 g·m^-2·a^-1）4个氮处理进行氮沉降模拟试验，测定3种菊科杂草种子萌发、幼苗生长及生理指标，探究菊科杂草对氮沉降的响应规律。结果表明：蒲公英、鬼针草的发芽指标随氮浓度增加呈先增后降趋势，而紫茎泽兰的发芽势、发芽指数随氮浓度增加逐渐下降；在 2和6 g·m^-2·a^-1氮添加浓度下，蒲公英、鬼针草、紫茎泽兰的株高、根长、干重等指标均得到促进，但当氮添加浓度升高到12 g·m^-2·a^-1时，这些指标均受到抑制；三种植物的胞间CO₂浓度随氮浓度增加呈先降后升趋势，而叶绿素含量的变化趋势与之相反。蒲公英、鬼针草净光合速率随氮浓度增加呈现“低促高抑”的特点，而紫茎泽兰的净光合速率在整个氮浓度梯度下均受到持续抑制。说明中低水平氮沉降可促进菊科杂草萌发与生长，助其种群扩张，而高水平氮沉降可能会限制其繁殖扩散。

关键词: 氮沉降, 菊科杂草, 种子萌发, 幼苗生长, 光合特性