Root herbivory and soil carbon cycling: Shedding “green” light onto a “brown” world

Roots play an important role in the formation and turnover of soil organic matter (SOM). Biological processes in the rhizosphere have the capacity to regulate the input of root materials to soil and the fate of root-derived carbon (C) in soil. While some aspects of rhizosphere ecology have received considerable research attention, one potentially important biotic driver, root herbivory, has been largely overlooked. In this study, we first review the literature on root herbivory, revealing that belowground herbivores can have substantial effects on the quality, quantity, and timing of belowground plant inputs to soil. Next, we introduce a conceptual framework in which root herbivory presents a distinct conduit that transfers C from living plants (the “green” world) to soil (the “brown” world). We also argue that direct and indirect interactions between root herbivores and the rhizosphere microbiome and other soil fauna can have significant impacts on soil microbial activities and soil C cycling. Finally, we outline key questions and topics for future research that incorporate belowground plant-herbivore interactions into soil biogeochemistry in an effort to improve our understanding of C flow in the rhizosphere and sharpen future predictions of soil C storage under changing environments. •A conceptual framework for root herbivory effects on soil C cycling is described.•Root herbivores drive C flow from roots to soil.•Root herbivore-induced inputs affect soil microbial activity and soil C cycling.•Important interactions between root herbivores and other soil biota are discussed.•Environmental changes may affect root herbivores and their impact on soil C storage.