关键词: 氮沉降, 菊科杂草, 种子萌发, 幼苗生长, 光合特性

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