Manipulation of vegetation with activated carbon reveals the role of root exudates in shaping native grassland communities

Abstract Question Plant community assembly has traditionally been viewed from the perspective of plant resource niches and competition and, more recently, facilitation in stressful environments. However, plants also engage in biotic interactions with neighbours and soil microbiome by producing chemically diverse root exudates. Root exudates have the potential to affect plant community productivity and composition by mediating plant interactions, fostering beneficial microbial interactions and affecting nutrient cycling. However, empirical evidence for the role of root exudates in plant community dynamics is still lacking, particularly under field conditions. Location Two calcareous grasslands in Western Estonia, Europe. Methods We tested the role of root exudates in shaping plant community productivity and composition by applying activated carbon powder, known to adsorb root exudates from soil solution, to two intact species‐rich grasslands. The experiment continued for four years and was combined with fertiliser application. Results We found that the application of activated carbon triggered significant changes in root morphology, plant productivity and growth form composition that were distinct from the effects of fertilisation. Community responses were site‐specific and varied with the duration of activated carbon application. Activated carbon addition increased the production of finer roots in a community with shallow soil in the first year of the experiment and significantly reduced above‐ground productivity at both sites by the end of the fourth growth season. The application of activated carbon promoted legume abundance at both sites and suppressed forb dominance at the site with shallow soil. Conclusion Our findings suggest that chemical interactions in the plant rhizosphere may play an important role in shaping grassland productivity and plant community composition. We also show that activated carbon can be used as an effective tool for manipulating plant interactions in intact grasslands occupied by long‐lived individuals.