Root traits with team benefits: understanding belowground interactions in intercropping systems

Abstract

Background The potential benefits of intercropping are manifold and have been repeatedly demonstrated. Intercropping has the potential to create more productive and resilient agroecosystems, by improving land utilisation, yield and yield stability, soil quality, and pest, disease and weed suppression. Despite these potential benefits, significant gaps remain in the understanding of ecological mechanisms that govern the outcomes when crop species are grown together. A major part of plant-plant interactions takes place belowground and these are often overlooked. Scope This review synthesises current evidence for belowground plant-plant interactions of competition, niche differentiation and facilitation, with the aim of identifying root traits that influence the processes contributing to enhanced performance of intercrops compared with monocultures. We identify a suite of potentially complementary root traits for maximising the benefits of intercropping. These traits underpin improved soil exploration, more efficient resource use, and suppression of soil-borne pathogens and pests in intercrops. Conclusion This review brings together understanding of the mechanisms underpinning interactions between intercropped roots, and how root traits and their plasticity can promote positive outcomes. Root trait ‘ideotypes’ for intercropped partners are identified that could be selected for crop improvement. We highlight the importance of examining belowground interactions and consider both spatial and temporal distribution of roots and rhizosphere mechanisms that aid complementarity through niche differentiation and facilitation. Breeding of crop ideotypes with specific beneficial root traits, combined with considerations for optimal spatio-temporal arrangement and ratios of component crops, are essential next steps to promote the adoption of intercropping as a sustainable farming practice.

Supply Chain Perspectives on Breeding for Legume–Cereal Intercrops

“…legume root exudates (Homulle et al, 2021) and physical support to prevent lodging. One of the main challenges for improving intercrops is characterizing the trait combinations that maximize these positive interactions while minimizing negative interactions (Brooker et al, 2021;Homulle et al, 2021;Justes et al, 2021).…”

“…The main advantage of intercrops is often described as being the result of the “4C effects” ( Justes et al, 2021 ) corresponding to three positive interactions (complementarity, cooperation, and compensation) and one negative interaction (competition) occurring simultaneously and dynamically between species over the whole cropping cycle. Positive legume–cereal interactions are underpinned by mechanisms of niche differentiation, such as for soil mineral nitrogen vs. biological nitrogen fixation ( Bedoussac et al, 2015 ; Cowden et al, 2021 ), and facilitation, such as soil phosphate release by legume root exudates ( Homulle et al, 2021 ) and physical support to prevent lodging. One of the main challenges for improving intercrops is characterizing the trait combinations that maximize these positive interactions while minimizing negative interactions ( Brooker et al, 2021 ; Homulle et al, 2021 ; Justes et al, 2021 ).…”

“…Positive legume–cereal interactions are underpinned by mechanisms of niche differentiation, such as for soil mineral nitrogen vs. biological nitrogen fixation ( Bedoussac et al, 2015 ; Cowden et al, 2021 ), and facilitation, such as soil phosphate release by legume root exudates ( Homulle et al, 2021 ) and physical support to prevent lodging. One of the main challenges for improving intercrops is characterizing the trait combinations that maximize these positive interactions while minimizing negative interactions ( Brooker et al, 2021 ; Homulle et al, 2021 ; Justes et al, 2021 ). The intercrop ideotypes that optimize these processes will vary with the intended outcome, whether to increase fertilizer use efficiency, minimize lodging, improve weed control, or promote biodiversity ( Brooker et al, 2015 ; Gu et al, 2021 ; Homulle et al, 2021 ).…”

“…One of the main challenges for improving intercrops is characterizing the trait combinations that maximize these positive interactions while minimizing negative interactions ( Brooker et al, 2021 ; Homulle et al, 2021 ; Justes et al, 2021 ). The intercrop ideotypes that optimize these processes will vary with the intended outcome, whether to increase fertilizer use efficiency, minimize lodging, improve weed control, or promote biodiversity ( Brooker et al, 2015 ; Gu et al, 2021 ; Homulle et al, 2021 ). Identifying clear goals to be achieved by intercropping is crucial when choosing candidate germplasm in the selection process, as different goals may necessitate separate breeding programs or simply the correct selection of existing genotypes.…”

Soil Bacterial and Fungal Communities Response Differently to Bombax Ceiba (Malvaceae) in a Traditional Agroforestry System

“…The ecological interactions of trees and crops are very complex that could be complementary or competitional (Querné et al 2017;Hombegowda et al 2020). For instance, trees take up nutrients from deep soil layers while crops drawing nutrients from topsoil layers, thereby shaping a complementary interaction in resource utilization (Hombegowda et al 2020;Homulle et al 2021). Furthermore, these nutrients absorbed by trees will return to the topsoil of arable land by litter decomposition (Isaac and Borden 2019).…”