Levine Jonathan M, Hacker Sally D, Harley Christopher D G, Bertness Mark D
Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA, , , , , , US.
Oecologia. 1998 Nov;117(1-2):266-272. doi: 10.1007/s004420050657.
Nutrients can structure communities by influencing both plant interactions and plant herbivore interactions, though rarely do studies integrate these processes. In this study we examined how nitrogen fertilization influenced (1) the positive interaction between the marsh elder, Iva frutescens, and the black rush, Juncusgerardi, and (2) the quality of Iva as a host plant for the aphid, Uroleuconambrosiae. Previous studies have shown that by mitigating soil salt accumulation and hypoxia, Juncus is essential to the survival of Iva and its aphid herbivore at mid-marsh elevations. To address the effects of nitrogen on this interaction, we compared fertilized and unfertilized Iva plants subject to Juncus removal and control treatments in the field. Additionally, we measured the monthly population growth rates of aphids transplanted onto these Iva plants. Iva leaf biomass and flower number results indicated that fertilizing Iva eliminated its dependence upon Juncus, such that fertilized plants grown without Juncus were not different from unmanipulated plants. Aphid monthly population growth rates through mid-summer revealed that fertilization also eliminated the indirect dependency of aphids on Juncus, so that aphid growth rates on fertilized Iva without Juncus neighbors were similar to rates on unmanipulated Iva. Results also indicated that fertilizing Iva grown with Juncus increased Iva size, potentially enabling these plants to support larger aphid populations. Our results suggest that only under conditions of nitrogen limitation are the positive effects of Juncus essential to the mid-marsh persistence of Iva and its aphid herbivore. Furthermore, we found that nitrogen effects on aphid populations may arise not only from a direct effect of nutrients on Iva size but also through the indirect effects of nitrogen on the interaction between Juncus and Iva. We argue that studies integrating processes occurring both within and between trophic levels, are important to fully understanding the community-wide effects of nutrients.
营养物质可以通过影响植物间相互作用以及植物与食草动物间相互作用来构建群落结构，不过很少有研究将这些过程整合起来。在本研究中，我们探究了施氮如何影响：（1）湿地接骨木（Iva frutescens）与黑灯心草（Juncus gerardi）之间的正向相互作用；（2）湿地接骨木作为菊小长管蚜（Uroleucon ambrosiae）寄主植物的质量。先前的研究表明，通过减轻土壤盐分积累和缺氧状况，灯心草对于湿地接骨木及其蚜虫食草动物在潮间带中部海拔高度的生存至关重要。为了研究氮对这种相互作用的影响，我们在田间比较了施以氮肥和未施氮肥的湿地接骨木植株，这些植株分别进行了去除灯心草和对照处理。此外，我们测量了移植到这些湿地接骨木植株上的蚜虫的月种群增长率。湿地接骨木的叶片生物量和花数量结果表明,对湿地接骨木施肥消除了其对灯心草的依赖，以至于在没有灯心草的情况下生长的施肥植株与未处理植株没有差异。整个仲夏期间蚜虫的月种群增长率表明，施肥也消除了蚜虫对灯心草的间接依赖，因此在没有灯心草邻株的施肥湿地接骨木上蚜虫的生长速率与未处理的湿地接骨木上的速率相似。结果还表明，对与灯心草一起生长的湿地接骨木施肥会增加湿地接骨木的大小，这可能使这些植株能够支持更大的蚜虫种群。我们的结果表明，只有在氮限制条件下，灯心草的正向作用对于湿地接骨木及其蚜虫食草动物在潮间带中部的持续存在才是必不可少的。此外，我们发现氮对蚜虫种群的影响可能不仅源于营养物质对湿地接骨木大小的直接影响，还源于氮对灯心草和湿地接骨木之间相互作用的间接影响。我们认为，整合营养级内部和营养级之间发生的过程的研究，对于全面理解营养物质对整个群落的影响很重要。
