Quantification of differences in root system architecture under maize/soybean interspecific interactions

Root system architecture determines the ability of crop in water and nutrient uptake, which affects interspecific facilitation in the maize/soybean intercropping. In this study, field experiments were conducted to investigate the differences of adult root system architecture between maize (Zea mays L.)/soybean (Glycine max L.) intercropping and monocropping. The skeleton of root system was captured with 3D digitalization at filling stage of maize, then the roots were sampled and scanned. Root length and root diameter were extracted from the scanned root images. Root overlap of maize and soybean were calculated by counting the percentage of the points located on axile roots of one plant inside root system of another plant to quantify the interspecific interactions in 3D. The results showed that root-root interactions between maize and soybean altered the root system architecture of both crops. The early axile roots of maize and soybean longer than the late axile roots in two cropping patterns. Maize/soybean interspecific interactions promoted axile root elongation of maize and soybean. The asymmetric interspecific facilitation was found in diameter of axile roots, which was the late axile roots of intercropped maize significantly thicker but most axile roots of intercropped soybean significantly thinner (ANOVA, P < 0.05). Root overlap of maize and soybean in intercropping was about 4.58% and mainly distributed 20~40 cm below soil surface. The axile roots of N1~N3 of maize trended to flatly grow first and rapidly grow downward later, mainly leading to the overlap between maize and soybean root system.