Plants can have strong effects on the biotic environment in the soil surrounding their roots. These effects are often plant-species specific and can persist in the soil after the plant disappears. These soil legacy effects can, in turn, have strong effects on plants that grow subsequently in the same soil (a process known as plant-soil feedback, PSF). In recent years it has been shown that these soil legacies not only affect plants, but also aboveground insect herbivores. Mechanisms have, to date, not been adequately described, but it is likely that traits related to growth and allocation of defence responses in the host plant play an important role. We hypothesized that plants that experience more negative PSFs would be poorly defended and thus would make more suitable host plants for herbivores. We further expected that nutritional and functional traits of the plant would be related to how plants and aboveground insects respond to species-specific legacy effects in the soil. Using twelve common grass and forb species that differ in growth rate we examined the relationship between soil legacy effects and the performance of aboveground herbivores on these plants.
Results/Conclusions
Contrary to our expectations, there was a positive correlation between the strength of both conspecific and heterospecific PSF and the performance of herbivores on the plant species. Interestingly, the effect in the latter was driven mostly by forbs, whereas in the former, the relationship was observed for grasses and forbs.
There was a negative relationship between nutritional characteristics of a plant species and the effect that the plant species has, via influencing the soil, on future herbivores on plant species that grow in the conditioned soil. This may help plants that invest in high quality tissues secure survival of future generations by leaving a legacy that is negative to herbivores.
We show positive relationships between both conspecific and heterospecific PSF effects of a plant species and the effects that their soils have on the performance of a future herbivore.
This phenomenon has to our knowledge not been shown before and we argue that, although pathogens generally accumulate in soils around a plant’s roots, vulnerable plants may also invest in recruiting beneficial soil organisms to their roots that may contribute to defence against future attackers aboveground and alleviate the impacts of fighting simultaneous attackers above- and belowground in the future.