Mutikainen Pia, Walls Mari
Laboratory of Ecological Zoology, Department of Biology, University of Turku, FIN-20500, Turku, Finland.
Oecologia. 1995 Dec;104(4):487-495. doi: 10.1007/BF00341346.
We studied the effects of environmental factors on the ability to compensate for simulated herbivory in an annual (Urtica urens) and two perennial (U. dioica subspp. dioica and sondenii) nettle species in order to test the compensatory continuum hypothesis. Further, we studied the expression of costs of structural defence in different environmental conditions. Herbivory interacted significantly with density and fertilization for height growth, branching and reproductive traits. The negative effects of simulated herbivory on relative height growth were less detrimental for plants grown in low density and high fertilization level, which supports the compensatory continuum hypothesis. However, with respect to other traits measured, our results do not support the idea of compensatory continuum. The negative effects of apical excision on inflorescence biomass were relatively more prominent in plants growing at low density and receiving more fertilization than on those growing in worse conditions. In addition, branching was reduced by apical excision regardless of resource levels. The lack of compensation for herbivory is explained by the role which the damaged or removed tissue plays in plant development and function. In the perennial U. dioica, defensive responses to herbivory, measured as changes in trichome density, were stronger than in the annual U. urens. In the southern subspecies dioica, trichome density increased in newly emerged leaves after leaf clipping. In the northern subspecies sondenii, trichome density increased after apical excision. The differences in the defensive responses between the two subspecies of U. dioica may be due to differential natural herbivory pressures on subspecies inhabiting different geographical regions. We observed negative phenotypic correlations between structural defence and other plant traits, which suggests the existence of costs of defence. In addition to differences among the species studied, the expression of costs of defence was dependent on the resource levels.
为了验证补偿连续体假说，我们研究了环境因素对一年生荨麻（小荨麻）和两种多年生荨麻（异株荨麻亚种异株荨麻和桑德尼荨麻）补偿模拟食草作用能力的影响。此外，我们还研究了不同环境条件下结构防御成本的表现。食草作用与密度和施肥对株高生长、分枝和繁殖性状有显著的相互作用。模拟食草作用对相对株高生长的负面影响，对低密度和高施肥水平下生长的植物危害较小，这支持了补偿连续体假说。然而，对于所测量的其他性状，我们的结果并不支持补偿连续体的观点。顶芽切除对花序生物量的负面影响，在低密度和施肥较多的植物中比在生长条件较差的植物中相对更显著。此外，无论资源水平如何，顶芽切除都会减少分枝。对食草作用缺乏补偿的原因，是受损或去除的组织在植物发育和功能中所起的作用。在多年生的异株荨麻中，以毛状体密度变化衡量的对食草作用的防御反应，比一年生的小荨麻更强。在南方亚种异株荨麻中，叶片修剪后新长出叶片的毛状体密度增加。在北方亚种桑德尼荨麻中，顶芽切除后毛状体密度增加。异株荨麻两个亚种防御反应的差异，可能是由于居住在不同地理区域的亚种受到的自然食草压力不同。我们观察到结构防御与其他植物性状之间存在负表型相关性，这表明存在防御成本。除了所研究物种之间的差异外，防御成本的表现还取决于资源水平。
