Unfolding the link between multiple ecosystem services and bundles of functional traits to design multifunctional crop variety mixtures

In face of the current environmental challenges, developing multifunctional cropping systems is increasingly needed, and crop variety mixtures are particularly interesting since they can deliver diverse services including grain production, yield stability, N₂O production regulation, disease control, and reduction of N-fertilizer losses. However, the relationships between intraspecific diversity and ecosystem multifunctionality are poorly understood so far, and practitioners lack science-based guidance to design mixtures. We used a pool of 16 bread wheat varieties classified into 4 functional groups based on 26 below- and aboveground functional traits, to conduct a field trial (88 large plots cultivated with single varieties or mixtures of 2, 4, or 8 varieties), quantifying 15 provisioning and regulating services for each plot. To assess yield stability between local conditions and years, the trial was replicated at 4 other locations and for 2 years, using 2 managements each time. We analyzed how variety number and functional groups predicted the variance in services, and applied in an innovative manner the RLQ co-inertia analysis to relate the (variety × traits) matrix Q to a (plot × services) matrix R, using a (plot × variety) composition matrix L as a link. Our results show that using variety mixtures allowed delivery of baskets of services not reachable when cultivating single varieties, and that mixtures mitigated tradeoffs between different pairs of services. Variety number or functional groups poorly predicted the variance in services, but the RLQ approach allowed the identification of groups of plots delivering consistent baskets of services. Moreover, we demonstrated for the first-time significant relationships between specific baskets of services and bundles of variety traits. We discuss how our results increase our understanding of intraspecific diversity–agroecosystem multifunctionality relationships, and propose the next steps using our new approach to support practitioners for designing variety mixtures that provide particular baskets of services.