Kaplan Ian, Halitschke Rayko, Kessler André, Sardanelli Sandra, Denno Robert F
Department of Entomology, University of Maryland, College Park, Maryland 20742, USA.
Ecology. 2008 Feb;89(2):392-406. doi: 10.1890/07-0471.1.
A recent surge in attention devoted to the ecology of soil biota has prompted interest in quantifying similarities and differences between interactions occurring in above- and belowground communities. Furthermore, linkages that interconnect the dynamics of these two spatially distinct ecosystems are increasingly documented. We use a similar approach in the context of understanding plant defenses to herbivory, including how they are allocated between leaves and roots (constitutive defenses), and potential cross-system linkages (induced defenses). To explore these issues we utilized three different empirical approaches. First, we manipulated foliar and root herbivory on tobacco (Nicotiana tabacum) and measured changes in the secondary chemistry of above- and belowground tissues. Second, we reviewed published studies that compared levels of secondary chemistry between leaves and roots to determine how plants distribute putative defense chemicals across the above- and belowground systems. Last, we used meta-analysis to quantify the impact of induced responses across plant tissue types. In the tobacco system, leaf-chewing insects strongly induced higher levels of secondary metabolites in leaves but had no impact on root chemistry. Nematode root herbivores, however, elicited changes in both leaves and roots. Virtually all secondary chemicals measured were elevated in nematode-induced galls, whereas the impact of root herbivory on foliar chemistry was highly variable and depended on where chemicals were produced within the plant. Importantly, nematodes interfered with aboveground metabolites that have biosynthetic sites located in roots (e.g., nicotine) but had the opposite effect (i.e., nematodes elevated foliar expression) on chemicals produced in shoots (e.g., phenolics and terpenoids). Results from our literature review suggest that, overall, constitutive defense levels are extremely similar when comparing leaves with roots, although certain chemical classes (e.g., alkaloids, glucosinolates) are differentially allocated between above- and belowground parts. Based on a meta-analysis of induced defense studies we conclude that: (1) foliar induction generates strong responses in leaves, but much weaker responses in roots, and (2) root induction elicits responses of equal magnitude in both leaves and roots. We discuss the importance of this asymmetry and the paradox of cross-system induction in relation to optimal defense theory and interactions between above- and belowground herbivory.
最近，对土壤生物群生态学的关注度激增，这引发了人们对量化地上和地下群落中相互作用的异同的兴趣。此外，越来越多的文献记录了连接这两个空间上不同生态系统动态的联系。在理解植物对食草动物的防御方面，我们采用了类似的方法，包括它们如何在叶和根之间分配（组成型防御）以及潜在的跨系统联系（诱导型防御）。为了探讨这些问题，我们采用了三种不同的实证方法。首先，我们对烟草（Nicotiana tabacum）的叶和根进行了食草动物处理，并测量了地上和地下组织次生化学的变化。其次，我们回顾了已发表的研究，这些研究比较了叶和根之间的次生化学水平，以确定植物如何在地上和地下系统中分配假定的防御化学物质。最后，我们使用荟萃分析来量化诱导反应对不同植物组织类型的影响。在烟草系统中，咀嚼叶片的昆虫强烈诱导叶片中次生代谢物水平升高，但对根的化学性质没有影响。然而，线虫对根的取食引发了叶和根的变化。几乎所有测量的次生化学物质在由线虫诱导形成的虫瘿中都有所升高，而根食草动物对叶化学性质的影响则高度可变，这取决于化学物质在植物体内的产生部位。重要的是，线虫干扰了在根中具有生物合成位点的地上代谢物（例如尼古丁），但对在地上部分产生的化学物质（例如酚类和萜类）却有相反的影响（即线虫提高了叶中的表达）。我们的文献综述结果表明，总体而言，将叶与根进行比较时，组成型防御水平极为相似，尽管某些化学类别（例如生物碱、芥子油苷）在地上和地下部分的分配有所不同。基于对诱导防御研究的荟萃分析，我们得出以下结论：（1）叶诱导在叶中产生强烈反应，但在根中反应较弱；（2）根诱导在叶和根中引发同等程度的反应。我们讨论了这种不对称性的重要性以及跨系统诱导的悖论与最优防御理论以及地上和地下食草动物之间相互作用的关系。
