The overall effect of a live soil inoculum collected from nature on plant biomass is often negative. One hypothesis to explain this phenomenon is that the overall net pathogenic effect of soil microbial communities reduces plant performance. Induced plant defenses triggered by the application of the plant hormones jasmonic acid (JA) and salicylic acid (SA) may help to mitigate this pathogenic effect of live soil. However, little is known about how such hormonal application to the plant affects the soil and how this, in turn, impacts plant growth. We grew four plant species in sterilized and inoculated live soil and exposed their leaves to two hormonal treatments (JA and SA). Two species (Jacobaea vulgaris and Cirsium vulgare) were negatively affected by soil inoculation. In these two species foliar application of SA increased biomass in live soil but not in sterilized soil. Two other species (Trifolium repens and Daucus carota) were not affected by soil inoculum and for these two species foliar application of SA reduced plant biomass in both the sterilized and live soil. Application of JA reduced plant biomass in both soils for all species. We subsequently carried out a multiple generation experiment for one of the plant species, J. vulgaris. In each generation, the live soil was a mixture of 10% soil from the previous generation and 90% sterilized soil and the same hormonal treatments were applied. The negative effects of live soil on plant biomass were similar in all four generations, and this negative effect was mitigated by the application of SA. Our research suggests that the application of SA can mitigate the negative effects of live soil on plant growth. Although the inoculum of soil containing a natural live soil microbial community had a strong negative effect on the growth of J. vulgaris, we found no evidence for an increase or decrease in negative plant-soil feedback in either the control or the SA treated plants. Also plant performance did not decrease consistently with succeeding generations.

从自然界收集的活土壤接种物对植物生物量的总体影响通常是负面的。解释这种现象的一个假设是土壤微生物群落的整体净致病作用降低了植物的性能。由应用植物激素茉莉酸 (JA) 和水杨酸 (SA) 引发的诱导植物防御可能有助于减轻活土壤的这种致病作用。然而，对于植物的这种激素应用如何影响土壤以及这反过来又如何影响植物生长知之甚少。我们在经过消毒和接种的活土壤中种植了四种植物，并将它们的叶子暴露于两种激素处理（JA 和 SA）。两个物种（Jacobaea vulgaris和Cirsium v​​ulgare) 受到土壤接种的负面影响。在这两个物种中，叶面施用 SA 增加了活土壤中的生物量，但不会增加无菌土壤中的生物量。其他两个物种（白三叶和Daucus carota）不受土壤接种物的影响，对于这两个物种，叶面施用 SA 降低了无菌土壤和活土壤中的植物生物量。JA 的应用减少了所有物种在两种土壤中的植物生物量。我们随后对其中一种植物J. vulgaris进行了多代实验. 在每一代中，活土都是 10% 的上一代土壤和 90% 的无菌土壤的混合物，并应用了相同的激素处理。活土对植物生物量的负面影响在所有四代中都相似，而这种负面影响通过 SA 的应用得到了缓解。我们的研究表明，SA 的应用可以减轻活土壤对植物生长的负面影响。尽管含有天然活土壤微生物群落的土壤接种物对J. vulgaris的生长具有强烈的负面影响，但我们没有发现对照或 SA 处理植物中植物 - 土壤负反馈增加或减少的证据。此外，植物性能并没有随着后代而持续下降。