Species interactions exert important influences on biodiversity and ecosystem stability. In complex natural communities, species interactions have gone beyond pairwise mechanisms, as interactions between two species can be regulated by one or more other species (higher-order species interactions). However, few studies consider higher-order interactions among organisms that are indirectly contacted, particularly under high soil nutrient conditions. Here, we performed a common garden experiment to investigate how natural herbivory (aboveground weevil) and simulated herbivory (leaf clipping) affect plant () interactions with soil antagonists (root-knot nematodes) and mutualists (arbuscular mycorrhizal fungi; AMF) under nitrogen and phosphorus addition. We also tested the effects of nitrogen, phosphorus, and herbivory-stimuli on leaf extrafloral nectary (EFN) production. We found that can compensate for biomass loss caused by clipping or weevil feeding, moreover, high nitrogen availability caused plant biomass to outpace herbivory-stimuli. Plant–antagonist (root-knot nematodes) interactions were not affected by clipping or weevil feeding under ambient nitrogen condition but were reduced by clipping or weevil feeding under high nitrogen supply, however, we did not find the same pattern under phosphorus addition. Aboveground herbivory-stimuli did not affect plant–mutualist (AMF) interactions, whether fertilized or not. In addition, nitrogen addition stimulated plants to secrete more EFN against clipping but did not increase EFN production against weevil feeding. Clipping and weevil feeding exhibited consistent effects on both plant–antagonist (root-knot nematodes) interactions and plant–mutualist (AMF) interactions. These results suggest that aboveground antagonists mainly mitigate belowground plant–antagonist interactions but not affect plant–mutualist interactions, and higher-order species interactions depend on nitrogen addition but not phosphorus addition.

中文翻译：

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地上拮抗剂减轻地下植物与拮抗剂的相互作用，但不影响植物与互利共生的相互作用

物种相互作用对生物多样性和生态系统稳定性产生重要影响。在复杂的自然群落中，物种相互作用已经超越了成对机制，因为两个物种之间的相互作用可以受到一个或多个其他物种的调节（高阶物种相互作用）。然而，很少有研究考虑间接接触的生物体之间的高阶相互作用，特别是在高土壤养分条件下。在这里，我们进行了一个常见的花园实验，以研究天然食草动物（地上象鼻虫）和模拟食草动物（剪叶）如何影响植物与土壤拮抗剂（根结线虫）和共生体（丛枝菌根真菌；AMF）在氮气和磷添加。我们还测试了氮、磷和草食刺激对叶外花蜜腺 (EFN) 产生的影响。我们发现，这可以补偿由修剪或象鼻虫取食引起的生物量损失，此外，高氮利用率导致植物生物量超过食草刺激。植物-拮抗剂（根结线虫）相互作用在环境氮条件下不受修剪或象鼻虫取食的影响，但在高氮供应下通过修剪或象鼻虫取食而减少，然而，我们在磷添加下没有发现相同的模式。无论受精与否，地上食草刺激不会影响植物互惠（AMF）相互作用。此外，添加氮会刺激植物分泌更多的 EFN 来对抗修剪，但不会增加 EFN 的产量来对抗象鼻虫的取食。修剪和象鼻虫取食对植物-拮抗剂（根结线虫）相互作用和植物-互利共生（AMF）相互作用表现出一致的影响。这些结果表明，地上拮抗剂主要减轻地下植物与拮抗剂的相互作用，但不影响植物与互利共生的相互作用，而高阶物种相互作用取决于氮的添加，而不是磷的添加。