Above‐ and belowground insect herbivores mediate the impact of nitrogen eutrophication on the soil food web in a grassland ecosystem

Abstract

Insect herbivores are important drivers of ecosystem processes in grasslands, and can mediate the grassland's response to environmental change. For example, recent evidence shows that above‐ and belowground herbivory, individually and in combination, can modify how a plant community responds to nitrogen (N) eutrophication, an important driver of global change. However, knowledge about how such effects extend to the associated soil food web is lacking. In a mesocosm experiment, we investigated how communities of soil nematodes – an abundant and functionally important group of soil organisms – responded to above‐ and belowground insect herbivory at contrasting N levels. We found that the strongest influence of above‐ and belowground herbivory on the nematode community appeared at elevated N. The abundance of root‐feeding nematodes increased when either above‐ or belowground insect herbivores were present at elevated N, but when applied together the two herbivore types cancelled out one another's effect. Additionally, at elevated N aboveground herbivory increased the abundance of fungal‐feeders relative to bacterial‐feeders, which indicates changes in decomposition pathways induced by N and herbivory. Belowground herbivory increased the abundance of omnivorous nematodes. The shifts in both the herbivorous and detrital parts of the soil food web demonstrate that above‐ and belowground herbivory does not only mediate the response of the plant community to N eutrophication, but in extension also the soil food web sustained by the plant community. We conclude that feedbacks between effects of above‐ and belowground herbivory mediate the response of the grassland ecosystem to N eutrophication.

Combined effects of aboveground herbivores and belowground microorganisms on dynamics of soil nematode communities in grassland mesocosms

“…This contradiction may be explained by the difference of aphid species or nematode species used in the two studies (Rasmann, 2022;Lima da Silva et al, 2020). The result that significant effects of aphid introduction on plant community were not extrapolated to soil nematodes via above-belowground linkages also contrasts with other studies (Borgström et al, 2018). This inconsistence may be due to the high complexity of plant community used in our study, in which each plant species may be specific in mediating the outcome of three-way interactions among aboveground aphids, plants, and soil nematodes, and this likely diminishes the overall above-belowground biotic linkages (Zhang et al, 2020).…”

Antagonistic interactions between above- and belowground biota reduce their negative effects on a tree species

“…Our findings indicate that the simultaneous presence of different attackers can lead to interactions that partly mitigate the negative effects of one attacker by another. This suggests that plants have developed strategies to cope with simultaneous damage by above-and belowground attackers because plants are often attacked by a wide diversity of above-and belowground organisms in natural ecosystems (Borgstrom et al 2018;Erwin et al 2014;Heinen et al 2018a, b;Huang et al 2014;Meier and Hunter 2018;Scherber et al 2010). Most importantly, these results highlight the importance of considering the roles of diverse above-and belowground species and their interactions in regulating plant growth and population dynamics.…”