Belowground processes and sustainability in agroecosystems with intercropping

Background and aims Crop diversity has been repeatedly shown to support multiple ecosystem functions, both directly and indirectly, driven by interspecific root-root interactions. Despite continuous advances in this field, some research gaps remain, and we need to pay more attention to the design and management of multi-species and multi-cultivar systems in the future. Scope We review advances in intercropping in enhanced ecosystem functioning in competition-based and facilitation-based intercropping systems via root-root interactions. We also consider recent achievements in yield stability and soil fertility. We address several perspectives to focus on towards more sustainable agriculture via intercropping or cultivar mixtures in the future. Conclusions In competition-based systems, scramble competition via root-root competition and contest competition involving allelochemicals offset yield advantages of target crop species. However, niche differentiation and selection of desirable crop combinations to minimize negative effects through secondary metabolites may also help to gain yield advantages in intercropping and cultivar mixtures. In facilitation-based systems, selecting genotypes of facilitated species with root traits that best match the facilitator may strengthen the facilitative interactions in resource enrichment and disease and pest control. We need more long-term research to explore the effects of belowground processes on soil fertility, ecosystem stability, adaptation, and mitigation of climate change to establish sustainable agroecosystems in the future. It is also urgent to develop new methods to link belowground processes to functioning in multi-species and multi-cultivar agroecosystems.