Root Plasticity and Root Trait Dissimilarity Drive Intercropping Overyielding Through Selection and Complementarity Effects

Selection and complementarity effects are generally considered to be mechanisms behind plant community overyielding, but these biodiversity effects are only partly understood in intercropping, especially for the role of species root traits under interspecific interactions. This study showed that root trait dissimilarity caused by root plasticity may contribute to selection effect, complementarity effect and yield advantage of intercropping. Soybean/maize, peanut/maize and the corresponding monocultures were grown in field plots with and without nitrogen (N) fertilization. Root traits (root length density, mean rooting depth, root mass density, mean root diameter, specific root length) were determined by taking five sampling sites in intercropping plots and two sampling sites in monocultured plots, with three soil depths (0-20, 20-40 and 40-60 cm). Root plasticity of community induced by species interactions had a positive effect on root trait dissimilarity (P<0.05), but there was not an obvious relationship between root plasticity of population (single crop) and root trait dissimilarity. Without N fertilization, root trait dissimilarity was positively related to root plasticity of community induced by species interactions (P<0.05), where the relationship between root plasticity and root trait dissimilarity was only significant in legume crops. With N fertilization, root plasticity of either community or population induced by species interactions did not affect root trait dissimilarity for both peanut/maize and soybean/maize intercropping. Overyielding, selection and complementarity effects were not significantly related to the root plasticity. However, selection effect increased with greater dissimilarity in root trait (P<0.05), and the overyielding was driven by the select effect at more than 50%. Moreover, root plasticity of maize under species interaction showed had a positive effect on the selection effect (P<0.05). Root plasticity enhances root trait dissimilarity, and to increase selection effect, and finally leads to a positive effect on the yield of intercropping.