意大利苍耳与乌拉尔甘草种间竞争能力比较

意大利苍耳已经开始入侵乌拉尔甘草农田，然而对其入侵后果目前知之甚少。通过研究意大利苍耳与乌拉尔甘草的种间竞争关系，以期为意大利苍耳对乌拉尔甘草农田生态系统的入侵能力及入侵后果的评估提供试验依据。模拟了甘草农田的土壤水肥条件，采用取代试验法，设置意大利苍耳与乌拉尔甘草的单种种植和混种种植2种种植模式，待意大利苍耳生育期结束后进行收获，分别比较了该两种植物的个体生长及生物量积累在单种种植与混种种植两种处理间的差异，并比较单种和混种模式下乌拉尔甘草的地下器官中甘草酸含量的差别，通过计算相对产量、相对竞争强度和竞争攻击系数来比较该两种植物种间竞争能力的相对强弱。结果表明：与单种模式相比，混种模式下意大利苍耳个体生长的形态学性状和有性繁殖能力均有显著增加，其株高、冠幅和种子数量较单种处理分别增加了13%、27%和56%。而乌拉尔甘草的个体生长及克隆繁殖能力均显著降低，其根瘤的形成也受到显著的抑制，混种处理的乌拉尔甘草的株高、冠幅、根总长度、根总表面积、根平均直径以及根瘤数量比单种处理分别下降了35%、45%、55%、63%、19%和76%。单种处理下每株甘草根状茎的平均条数为3条，而与意大利苍耳混种后，其根状茎的发育被完全抑制。与单种处理相比，混种处理中的意大利苍耳生物量积累均显著的增加了，其中根、茎、叶、果实及总生物量与单种模式相比分别增加了84%、73%、84%、73%和77%，而混种模式却极显著降低了乌拉尔甘草生物量和地下器官甘草酸含量的积累，使其根、茎、叶、总生物量以及甘草酸含量与单种模式相比分别下降了72%、80%、65%、71%和63%。混种模式中的意大利苍耳相对产量（RY_a）大于1，而乌拉尔甘草相对产量（RY_b）小于1，表明意大利苍耳受到邻株同种其他个体的种内竞争压力大于来自邻株乌拉尔甘草的种间竞争压力，而乌拉尔甘草受到邻株同种其他个体的种内竞争压力则小于来自邻株意大利苍耳的种间竞争压力。混种模式中的意大利苍耳相对竞争强度（RCI_a）小于0，其竞争攻击系数（A_q）大于0，而乌拉尔甘草的相对竞争强度（RCI_b）则在0-1之间，其竞争攻击系数（A_b）小于0，表明在该两种植物的混生群落中，乌拉尔甘草的竞争能力弱于意大利苍耳。总体来看，在二者混生的群落中，意大利苍耳在竞争中占据明显的优势地位，对乌拉尔甘草的产量和品质均造成强烈的负面影响。

Comparison of interspecific competitive ability between Xanthium italicum Moretti and Glycyrrhiza uralensis Fisch

Xanthium italicum Moretti has been invading farmland of Glycyrrhiza uralensis Fisch, but little is known about its impacts. Therefore, interspecific competition between the two species has been studied to provide an experimental evidence for evaluating the invasibility and effect of the presence of X. italicum on the G. uralensis population in farmland. Pot experiment was carried out and common soil water and fertilizer condition of the cultivated G. uralensis were simulated. Two treatments, monoculture and mixture of the two species, were conducted and a replacement experiment was adopted. All the plants were harvested at the end of the growing period of X. italicum, then growing status and biomass of each plant and glycyrrhizic acid concentration of G. uralensis between the two treatments were compared. The relative competitiveness ability of the two species was compared by relative yield, relative competitive intensity and aggressivity. The results showed that, compared with the monoculture treatment, the vegetative growth and seed production of X. italicum were significantly higher in the mixture treatment. The height, crown width and seed number of X. italicum under the mixture treatment increased by 13%, 27% and 56% respectively compared to those under the monoculture treatment. However, the individual growth and development of root nodule of G. uralensis were significantly inhibited as they grew together with the alien plant, because compared with the monoculture treatment, the height, crown width, total root length, total root surface area, average root diameter and the number of root nodules of G. uralensis under the mixture treatment decreased by 35%, 45%, 55%, 63%, 19% and 76%, respectively. There were three pieces of rhizomes per individual of G. uralensis on average under the monoculture treatment, but its rhizomes development was completely inhibited while being planted together with the invader. The biomass of X. italicum in the mixture treatment was significantly higher, and its root, stem, leaf, fruit and total biomass increased by 84%, 73%, 84%, 73% and 77%, respectively compared with those under the monoculture treatment. However, the mixture treatment significantly reduced the biomass and glycyrrhizic acid accumulation of G. uralensis, since its root, stem, leaf, total biomass and glycyrrhizic acid concentration decreased by 72%, 80%, 65%, 71% and 63%, respectively. The relative yield of X. italicum in the mixture treatment was more than 1, while that of G. uralensis was less than 1, which indicates that the pressure of intraspecific competition of X. italicum was greater than that of interspecific competition from the G. uralensis, and the pressure of intraspecific competition of G. uralensis was less than the pressure of interspecific competition from the X. italicum. Under the mixture treatment, the relative competitive intensity of X. italicum was less than 0, and its aggressivity was greater than 0, while the relative competitive intensity of G. uralensis was between 0 and 1, and its aggressivity was less than 0, which indicates that G. uralensis is less competitive than X. italicum when the two species coexist. In summary, the exotic plant X. italicum is of more strong competitiveness than G. uralensis, and the invader has a strong impact on the yield and quality of the licorice.