Resistance vs. surrender: Different responses of functional traits of soybean and peanut to intercropping with maize

Plants can modify their morphological or physiological traits in response to nutrient availability and to the presence and identity of neighboring individuals. However, few studies have addressed the effects of changes in above- and below-ground functional traits for the productivity advantage in intercropping. We hypothesized that the plasticity of above- and below-ground functional traits of crops in response to nutrients availability and interspecific interactions affects biomass of both crop species and whole intercropping systems. A 2-year field experiment was performed with two N levels (with and without), two P levels (with and without) and five cropping systems (i.e. sole maize, peanut and soybean, and maize/peanut and maize/soybean intercropping). We measured thirteen above- and below-ground functional traits related to light interception and use efficiency, root length and distribution at the grain filling stage of maize, and final biomass at harvest. Maize/peanut and maize/soybean intercrops has productivity advantages compared to monoculture, and this was mainly in terms of increases in maize biomass. Compared with monoculture, intercropping increased maize biomass more than it decreased soybean (24 %) or peanut (49 %) biomass. Maize had a yield advantage through greater leaf area, root length and root biomass density when intercropped. Intercropped soybean resisted suppression by maize through increased height and specific leaf area, but intercropped soybean had decreased specific leaf N and biomass. Branch number, leaf area, specific leaf nitrogen and root biomass density of peanut were all suppressed by maize, which caused a large decrease in peanut biomass when intercropped. Our study provides evidence that changes in above- and below-ground functional traits in response to nutrients availability and interspecific interactions are key to explaining patterns of transgressive overyielding. Our findings can help to better understand the underlying mechanisms that regulate productivity advantages in species mixtures, and have implications for the sustainable management of species-diverse food-production systems.