Abstract
Abstract Plants leave species‐specific legacies in the soil they grow in that can represent changes in abiotic or biotic soil properties. It has been shown that such legacies can affect future plants that grow in the same soil (plant–soil feedback, PSF). Such processes have been studied in detail, but mostly on individual plants. Here, we study PSF effects at the community level and use a trait‐based approach both in the conditioning phase and in the feedback phase to study how 12 individual soil legacies influence six plant communities that differ in root size. We tested if (1) grassland perennial species with large root systems would leave a stronger legacy than those with small root systems, (2) grass species would leave a more positive soil legacy than forbs, and (3) communities with large root systems would be more responsive than small‐rooted communities. We also tested (4) whether a leaf‐chewing herbivore and a phloem feeder were affected by soil legacy effects in a community framework. Our study shows that the six different plant communities that we used respond differently to soil legacies of 12 different plant species and their functional groups. Species with large root systems did not leave stronger legacies than species with small root systems, nor were communities with large root systems more responsive than communities with root systems. Moreover, we show that when communities are affected by soil legacies, these effects carry over to the chewing herbivore Mamestra brassicae (Lepidoptera: Noctuidae) through induced behavioural changes resulting in better performance of a chewing herbivore on forb‐conditioned soils than on grass‐conditioned soils, whereas performance of the phloem feeder Rhopalosiphum padi (Hemiptera: Aphididae) remained unaffected. Synthesis. The results of this study shed light on the variability of soil effects found in previous work on feedbacks in communities. Our study suggests that the composition of plant communities determines to a large part the response to soil legacies. Furthermore, the responses to soil legacies of herbivores feeding on the plant communities that we observed, suggests that in natural ecosystems, the vegetation history may also have an influence on contemporary herbivore assemblages. This opens up exciting new areas in plant–insect research and can have important implications for insect pest management.
Highlights
Soil biota critically depend on plants, because they provide the primary resources for the soil food web (Bardgett & Wardle, 2010; Wardle et al, 2004)
Our study shows that the six different plant communities that we used respond differently to soil legacies of 12 different plant species and their functional groups
We show that when communities are affected by soil legacies, these effects carry over to the chewing herbivore Mamestra brassicae (Lepidoptera: Noctuidae) through induced behavioural changes resulting in better performance of a chewing herbivore on forb-conditioned soils than on grass-conditioned soils, whereas performance of the phloem feeder Rhopalosiphum padi (Hemiptera: Aphididae) remained unaffected
Summary
Soil biota critically depend on plants, because they provide the primary resources for the soil food web (Bardgett & Wardle, 2010; Wardle et al, 2004). Plant roots directly interact with the soil and soil biota and plants with large root systems may have a larger zone of influence per unit soil, or a larger contact area for interacting with soil organisms than plants with small roots It is well known for many plant species that there is a positive relationship between the root size and root growth rate of a plant and the amount of exudates that the roots deposit in the soil (De Deyn, Cornelissen, & Bardgett, 2008; Dennis, Miller, & Hirsch, 2010; der Krift, Kuikman, Möller, & Berendse, 2001). We examine the effects of soil legacies on a selection of large- and small-rooted grasses and forbs (based on their accumulation of root biomass over 7 weeks) and in turn how this affects the performance of two generalist herbivores from different feeding guilds. We predicted that (1) large-rooted plants will create more negative soil legacies than small-rooted plants, and this will, in turn, affect above-ground herbivores; (2) legacies left by grasses will be more positive than legacies left by forbs; (3) large-rooted plant communities will be more responsive to soil legacies than small-rooted communities. (4) Lastly, we expected that the two insect species will be differentially affected by soil legacies
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