Abstract
Plant‐mediated soil legacy effects can be important determinants of the performance of plants and their aboveground insect herbivores, but, soil legacy effects on plant–insect interactions have been tested for only a limited number of host plant species and soils. Here, we tested the performance of a polyphagous aboveground herbivore, caterpillars of the cabbage moth Mamestra brassicae, on twelve host plant species that were grown on a set of soils conditioned by each of these twelve species. We tested how growth rate (fast‐ or slow‐growing) and functional type (grass or forb) of the plant species that conditioned the soil and of the responding host plant species growing in those soils affect the response of insect herbivores to conditioned soils. Our results show that plants and insect herbivores had lower biomass in soils that were conditioned by fast‐growing forbs than in soils conditioned by slow‐growing forbs. In soils conditioned by grasses, growth rate of the conditioning plant had the opposite effect, i.e. plants and herbivores had higher biomass in soils conditioned by fast‐growing grasses, than in soils conditioned by slow‐growing grasses. We show that the response of aboveground insects to soil legacy effects is strongly positively correlated with the response of the host plant species, indicating that plant vigour may explain these relationships. We provide evidence that soil communities can play an important role in shaping plant–insect interactions aboveground. Our results further emphasize the important and interactive role of the conditioning and the response plant in mediating soil–plant–insect interactions.
Highlights
Understanding what drives the performance of insect herbivores on their host plants has been an important area in the field of ecology
On average, standardized shoot and root biomass was higher in soils conditioned by grasses and slow-growing plants, than in soils conditioned by forbs or fast-growing plants, respectively
Standardized shoot and root biomass, on average, was higher when plants were grown in soils conditioned by slow-growing forbs, than when they were grown in soils conditioned by fast-growing forbs, whereas in soils conditioned by grasses, the effect of growth rate was weaker, but opposite (Fig. 1a and 1b significant Conditioning plant functional type (Cf) × Conditioning plant growth rate (Cg) interactions, Table 2)
Summary
Understanding what drives the performance of insect herbivores on their host plants has been an important area in the field of ecology. Roots, being embedded in the soil, encounter soil microorganisms and soil invertebrates, whereas aboveground structures, such as leaves or flowers, interact with insect herbivores or pollinators. A vast body of work has revealed how individual soil taxa can influence the performance of aboveground foliar feeding herbivores, mediated by the shared host plant (reviewed by Koricheva et al 2009, Pineda et al 2010, Johnson et al 2012, Wondafrash et al 2013). Soils are inhabited by a vast amount of different (micro) organisms, and how entire soil communities and the interactions within them can influence aboveground herbivore performance on different plant species is not well understood (Kostenko et al 2012, Pineda et al 2017, Heinen et al 2018a, b)
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