Induced resistance of plants reduces their negative soil‐legacy effects on natives but not on naturalized aliens

Plant invasions pose a threat to native biodiversity and are often mediated by below‐ground processes such as plant–soil feedback. Because induced defence responses can alter interactions between plants and soil biota, the strength may depend not only on plant origin but also on whether defence pathways have been activated during soil conditioning.

We tested how induced resistance mediated by jasmonic acid and salicylic acid in conditioning‐phase plants influences soil‐legacy effects on five pairs of native and naturalized alien focal plant species. In the conditioning phase, we grew the 10 focal species and 5 additional nonfocal native species. To activate defence pathways that are naturally induced by herbivores and pathogens, we sprayed them with jasmonic acid, salicylic acid or water (control). Thereafter, the five pairs of focal species were planted on the conditioned soils to test soil‐legacy effects.

Conditioned soils, particularly conspecific soils, pronouncedly reduced focal plant growth. In the absence of resistance induction in conditioning‐phase plants, native focal plants suffered stronger growth reductions than naturalized aliens. However, resistance induction largely mitigated this disadvantage, reducing differences in performance between native and naturalized alien plants.

Synthesis . Our findings indicate that induced resistance can reshape soil legacies that reduce the disadvantage of native plants relative to aliens, revealing an overlooked mechanism through which defence pathways interact with soils to influence plant invasions.