Overyielding is accounted for partly by plasticity and dissimilarity of crop root traits in maize/legume intercropping systems

Positive biodiversity-productivity relationships have been found in biodiversity field experiments of grasslands, forests and natural terrestrial ecosystems, where diversity effects were separated by complementarity (CE) and selection effects (SE). However, we know little about how CE and SE are related to root traits and root dissimilarity. A 4-year field experiment was carried out with a split-plot design, where main plot was four nitrogen (N) applications (N0, N1, N2 and N3) and five cropping systems (maize Zea mays L./soybean Glycine max L. Merrill., maize/peanut Arachis hypogaea L. intercropped and the corresponding monocultures) with three replicates. Roots were sampled in the N0 and N2 treatments in 2 years. Intercropping effects were analysed based on grain yield for 4 years and roots were sampled down to 60 cm depth, and analysed with morphological parameters at different crop growth stages in 2 years. Intercropping significantly increased grain yield and above-ground biomass in both intercropping systems under all N treatments. The partitioning of the net intercropping effects showed that yield advantage in intercropping was due to a positive CE under the N0 treatment, and to a positive SE with N application. Maize showed greater root morphological plasticity than the legumes did, with greater changes in root length density (RLD), root weight density (RWD) and total root surface (TS) in intercropping than in monoculture. Intercropped maize occupied a larger soil space, while lateral RLD distribution of legumes was decreased by maize. The RLD, RWD and TS of intercropped maize were constant or increased in later growth stages. SE showed a significantly positive relationship with root dissimilarity. Principal component analysis showed mean root depth and specific root length of legumes drove the positive CE in the absence of N fertilization. Root dissimilarity determined by maize explained the selection effects in overyielding. Complementarity effects under N0 were closely associated with specific root traits such as mean root depth and specific root length. Linking changes of root traits with intercropping effects above-ground helps understand yield advantages in diverse agroecosystem. In general, a cereal species with strong phenotypic plasticity intercropped with a legume species with strong physiological plasticity can maximize the yield advantage of intercropping. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

This study investigated the relationship between root traits, root dissimilarity, and intercropping effects. The results showed that intercropping significantly increased grain yield and above-ground biomass. Complementarity effects were mainly driven by specific root traits, such as root depth and specific root length, while selection effects were closely related to root dissimilarity.