The concept of hormesis describes that the application of low concentrations of a toxic compound will stimulate growth and activity of an organism. Since it is unknown whether hormesis occurs in arbuscular mycorrhizal fungi (AMF) the present work was designed to reveal whether two fungicides would generate hormetic response curves for AMF performance. The effect of mancozeb and carbendazim on performance of three AMF in symbioses with pea was investigated. The fungicides were mixed uniformly into irradiated soil at three field dose equivalents, which were 1x, 5x and 25x for mancozeb and 0.01x, 0.1x and 1x for carbendazim. A nil fungicide treatment was included for each fungus and a mesh-enclosed, ³³P-labelled soil patch enabled the measurement of AMF P uptake. Both fungicides generated biphasic response curves for AMF root colonization, which was largely enhanced by the two lower doses and suppressed by the highest. Besides, the lowest concentration of both fungicides increased the hyphal length-specific ³³P uptake by one of the fungi, while 0.1x carbendazim also increased the ³³P uptake by another. In contrast, the length of root-external hyphae was either decreased or unaffected by increasing fungicide doses. The biphasic fungicide responses of root colonization and hyphal P uptake were obtained in irradiated soil without AMF antagonists and therefore probably caused by direct effects on the AMF. Such hormetic response patterns may be common in ecosystems where AMF will usually be exposed to a range of abiotic and biotic stressors.

兴奋剂的概念描述了低浓度有毒化合物的应用将刺激生物体的生长和活性。由于尚不清楚丛枝菌根真菌（AMF）是否会发生兴奋剂，因此本研究旨在揭示两种杀菌剂是否会产生AMF性能的滴答反应曲线。研究了代森锰锌和多菌灵对三种AMF与豌豆共生的性能的影响。将杀真菌剂按三个野外剂量当量均匀混合到辐照的土壤中，当量的曼考昔布分别为1x，5x和25x，多菌灵为0.01x，0.1x和1x。每种真菌均包括无杀菌剂处理，并用网状封闭³³P标记的土壤斑块能够测量AMF P的吸收。两种杀真菌剂均产生了针对AMF根定植的双相响应曲线，这两个较低的剂量大大增强了该曲线，而最高的则抑制了这两个曲线。此外，两种杀菌剂的最低浓度增加了其中一种真菌的菌丝长度特异性³³ P吸收，而0.1x多菌灵也增加了³³磷吸收另一个。相反，根外菌丝的长度减少或不受杀真菌剂剂量增加的影响。在没有AMF拮抗剂的辐照土壤中获得了根部定植和菌丝P吸收的双相杀真菌剂反应，因此可能是由对AMF的直接影响引起的。在AMF通常会暴露于一系列非生物和生物应激源的生态系统中，这种令人讨厌的反应模式可能很常见。