Plant-soil feedback in belowground-aboveground interactions

Background/Question/Methods

Plant-soil feedback and belowground-aboveground interactions are currently two hot topics in ecology. In both research fields soil organisms play a central role, but so far these fields have developed separately. Plant-soil feedback studies focus on the effects of plants on the performance of other plants that grow later in the soil via changes in the composition or abundance of soil biota, or via changes in soil nutrients. Belowground-aboveground studies focus on the effects of root herbivores or other soil biota on aboveground insect herbivores and their natural enemies via changes in plant nutritional quality. The vast majority of plant-soil feedback studies have focused on the feedback effects on plant biomass without studying the effects on plant nutritional quality. However, interactions with soil biota such as bacteria, AMF, pathogenic fungi, or root feeding nematodes can also influence the chemical composition of both roots and aboveground plant parts. Belowground-aboveground studies, on the other hand, typically examine interactions that occur simultaneously and on a single plant, thereby ignoring the potential of legacy effects of herbivory on later growing plants via changes in soil biotic or abiotic conditions. However, both belowground and aboveground herbivory can influence the soil microbial community, for example via their effects on the amount or chemical composition of roots and root exudates. We will show (i) how plant-soil feedback effects influence belowground-aboveground interactions, and (ii) how belowground-aboveground interactions affect plant-soil feedback responses. 

Results/Conclusions

We will show how plant-soil feedback affects the amount and composition of primary and secondary plant compounds in the foliage of ragwort (Senecio jacobaea) plants, and how this affects the performance of foliar feeding insects. Further, we will show how aboveground and belowground insect herbivory on ragwort affects the composition of fungal pathogens in the soil, and via plant-soil feedback can influence the growth responses of ragwort plants that grow later in the soil. We argue that plant-soil feedback and belowground-aboveground interactions should be considered concurrently. Aboveground and belowground herbivory can have effects that go beyond a single growth period of a plant, and plant-soil feedback effects can be greatly affected by whether or not the plant is also exposed to aboveground or belowground herbivory during the conditioning phase.