结论:蚂蚁,但不是菌根,对马铃薯植物上的昆虫咀嚼草食动物有重大影响。然而,没有证据表明对食草动物的相互互动影响。植物与地上和地下互助者联系在一起,两个突出的例子是蚂蚁和丛枝菌根真菌(AMF),分别。虽然这两种相互关系都得到了广泛的研究,联合操作测试它们对植物的独立和交互(非加性)效应很少见。为了解决这个差距,我们通过咬叶昆虫攻击马铃薯(Solanumtuberosum)植物,对蚂蚁和AMF对食草动物的影响进行了联合测试,并进一步测量了植物性状,这些性状可能介导了对草食动物的共同作用。在现场实验中,我们通过因素操纵AMF(两个水平:对照和菌根化)和蚂蚁(两个水平:排除和存在)的存在,并量化了作为直接防御的叶片酚类化合物的浓度,以及可能直接介导的植物挥发性有机化合物(VOC)排放(例如,草食动物驱避剂)或间接(例如,蚂蚁引诱剂)防御。此外,我们测量了蚂蚁的丰度,并对VOC混合物的影响进行了双重选择温室实验测试(模仿对照与接种AMF的植物)对蚂蚁的吸引力作为间接防御机制。蚂蚁的存在显着减少了食草动物,而菌根化对食草动物和相互作用没有可检测的影响。植物性状测量表明,菌根对叶片酚类物质没有影响,但显着增加了VOC的排放。然而,菌根化不会影响蚂蚁的丰度,也没有证据表明AMF会通过蚂蚁介导的防御对草食性活动产生影响。始终如一,双重选择试验表明,AMF诱导的挥发性混合物对蚂蚁吸引力没有影响。一起,这些结果表明,马铃薯植物的食草动物主要响应自上而下(蚂蚁介导的)而不是自下而上(AMF介导的)控制,效应的不对称性,这可能排除了对草食动物的互惠非加性效应。对此进一步研究,以及其他工厂系统,需要检查生态环境,在这种环境下,互惠互动效应或多或少可能出现,以及它们对植物适应性和相关社区的影响。
CONCLUSIONS: Ants, but not mycorrhizae, significantly affected insect leaf-chewing
herbivory on potato plants. However, there was no evidence of mutualistic interactive effects on
herbivory. Plants associate with both aboveground and belowground mutualists, two prominent examples being ants and arbuscular mycorrhizal fungi (AMF), respectively. While both of these mutualisms have been extensively studied, joint manipulations testing their independent and interactive (non-additive) effects on plants are rare. To address this gap, we conducted a joint test of ant and AMF effects on
herbivory by leaf-chewing insects attacking potato (Solanum tuberosum) plants, and further measured plant traits likely mediating mutualist effects on
herbivory. In a field experiment, we factorially manipulated the presence of AMF (two levels: control and mycorrhization) and ants (two levels: exclusion and presence) and quantified the concentration of leaf phenolic compounds acting as direct defenses, as well as plant volatile organic compound (VOC) emissions potentially mediating direct (e.g., herbivore repellents) or indirect (e.g., ant attractants) defense. Moreover, we measured ant abundance and performed a dual-choice greenhouse experiment testing for effects of VOC blends (mimicking those emitted by control vs. AMF-inoculated plants) on ant attraction as a mechanism for indirect defense. Ant presence significantly reduced
herbivory whereas mycorrhization had no detectable influence on
herbivory and mutualist effects operated independently. Plant trait measurements indicated that mycorrhization had no effect on leaf phenolics but significantly increased VOC emissions. However, mycorrhization did not affect ant abundance and there was no evidence of AMF effects on herbivory operating via ant-mediated defense. Consistently, the dual-choice assay showed no effect of AMF-induced volatile blends on ant attraction. Together, these results suggest that herbivory on potato plants responds mainly to top-down (ant-mediated) rather than bottom-up (AMF-mediated) control, an asymmetry in effects which could have precluded mutualist non-additive effects on herbivory. Further research on this, as well as other plant systems, is needed to examine the ecological contexts under which mutualist interactive effects are more or less likely to emerge and their impacts on plant fitness and associated communities.