Indirect effect of earthworms on wheat-aphid interactions

The aboveground and belowground compartments of terrestrial ecosystems,
which are generally separated in interaction studies, are nevertheless
linked by their dependence on the same plant. Soil organisms can influence
interactions between plants and above-ground herbivores by changes in
plant growth and chemistry. In the present study, under controlled
conditions the direct influence of earthworms and aphids on wheat traits
(biomass; C and N content) was investigated. The effect of earthworms on
aphid reproduction was also investigated, in order to demonstrate the
indirect plant-trait-mediated effects. The results showed a significant
effect of both above and below-ground organisms on plant traits. Indeed,
wheat biomass and carbon and nitrogen contents were influenced by the
presence of earthworms and aphids, suggesting that earthworms can promote
aboveground and belowground plant growth by promoting resource
acquisition. Interestingly, the nitrogen content was significantly higher
in the presence of aphids or earthworms alone and it was even higher when
the two organisms were present together. Moreover, the results showed a
strong effect of earthworms on aphids, with a reproduction rate almost
twice as high as in the absence of earthworms. These results could have
implications for crop management, as they indicate that the presence of
earthworms compensate the negative effect of aphids on plant biomass,
probably by acting on nutrient uptake and plant defensive traits, despite
a higher aphid reproduction rate in the presence of earthworms probably
linked to nitrogen content. By addressing the effects of earthworms on
both the pest performances and plant traits, this study highlights the
need for further research on the indirect effects of below-ground
compartments on pest performance. This study builds towards a better
understanding of the interaction between soil, plant and herbivores and
highlights the importance to study the pest management with a more
holistic view of agroecosystems.