DOI: 10.5061/dryad.p5hqbzkrj
title: Overyielding is accounted for partly by plasticity and dissimilarity of crop root traits in maize/legume intercropping systems

description: Positive biodiversity-productivity relationships have been found in
 biodiversity field experiments of grassland, forestry, and other 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
 four-year field experiment was carried out with a split-plot design, where
 main plot was four nitrogen (N) applications (N0, N1, N2, 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 two years. Intercropping effects were analyzed based on
 grain yield for four years and roots were sampled down to 60 cm depth, and
 analyzed with morphological parameters at different crop growth stages in
 two years. Intercropping significantly increased grain yield and
 aboveground 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 aboveground 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.
description: This field experiment was
 arranged as a split-plot design with two factors from 2017 to 2020. The
 experimental factors included four N applications (N0, N1, N2 and N3) and
 five cropping systems, including maize (<em>Zea mays</em> L.
 cv. Xian-yu No.335)/soybean (<em>Glycine max</em> L. cv. Ji-yu No.47) intercropping, maize/peanut
 (<em>Arachis hypogaea</em> L. cv. Bai-sha No.1016)
 intercropping and the corresponding monocultures. The N application was
 set as the main-plot treatments, and the cropping system as the sub-plot
 treatments. The peanut
 monoculture as well as soybean monoculture received the same N-fertilizer
 applications, namely 0, 40, 80, and 120 kg N ha<sup>-1</sup>.
 For the maize monoculture, these were 0, 180, 240, and 300 kg N
 ha<sup>-1</sup>. The N applications for the maize/peanut
 intercrop were 0, 110, 160, and 210 kg N ha<sup>-1</sup>,
 consistent with that in the maize/soybean intercropping
 system. Each
 treatment had the same basal N application with four levels at 0, 40, 80,
 and 120 kg ha-1 N; the remaining N was equally applied twice at the
 jointing stage and pre-tasseling stage of maize. Each plot was 43.2 m2 (6
 m×7.2 m) in size, with 12
 rows (row distance was 0.6 m, plant distance was 0.17 m for maize and
 0.085 m for legumes). Two rows of maize intercropped with two rows of
 legumes constituted one strip in intercropping plots . Maize and soybean
 were sown in early May, and peanut sown in mid-May; all crops were
 harvested in late September to early
 October. The root samples were collected on July 20th in
 2017 and 2018 (when maize was at pre-tasseling stage and legumes at
 blooming stage), and on August 15th in 2018 (when maize and legumes were
 at filling). The roots of maize and legumes were
 distinguished by differences in color, texture, and branching pattern. The
 roots of maize were white and smooth, and the roots of legumes were brown
 with small nodules. Separated root fractions were scanned using an Epson
 Perfection V750 Pro and then analyzed with Win-RHIZO™ giving data of total
 root length and total root surface (TS) for each soil
 core.