Abstract: This study aimed to explore the effects of intercropping on root growth characteristics and carbon and nitrogen metabolism characteristics of some common forage crops. Five species monocultures (alfalfa, triticale, oat, maize and sweet sorghum) were used as reference crops in a field experiment, and four intercropping combinations (alfalfa/triticale, alfalfa/oat, alfalfa/maize and alfalfa/sweet sorghum) were evaluated. The root system growth of alfalfa and the four Poaceae crops under monoculture and intercropping were observed in situ through advanced minirhizotron and computer imaging technology, and the key enzymes and products of carbon and nitrogen metabolism under the four intercropping combinations were studied. It was found that the root parameters were very significantly (P<0.01) and positively correlated with carbon and nitrogen metabolism whether in monoculture or intercropping. Root length and surface area were significantly (P<0.05) and positively correlated with ribulose-1,5-bisphosphate carboxylase (RuBPCase) and nitrate reductase (NR) activity, and also with sucrose phosphate synthase (SPS) and glutamine synthetase (GS) activity, indicating that the root characteristics were consistent with carbon and nitrogen metabolism. Root length, root surface area and other root system parameters of the four tested Poaceae forages were significantly enhanced when intercropped with alfalfa, while alfalfa performance differed between monoculture and intercropped treatments. Root systems of alfalfa intercropped with maize and sweet sorghum were significantly inhibited (significantly smaller than in monocropping), and the alfalfa plants showed weak competitive ability. However, root systems of alfalfa intercropped with triticale and oat were unaffected. When intercropped with alfalfa, functional leaf RuBPCase and NR activities of the four Poaceae species were significantly increased, compared with monocropping. For alfalfa functional leaves, RuBPCase and NR activities of alfalfa plants intercropped with maize and sweet sorghum were significantly lower than in monoculture, while leaf enzyme activities of alfalfa intercropped with triticale and oat were not significantly changed, compared to monoculture. In summary, in this study the root system development of the tested forages mirrored the leaf carbon and nitrogen metabolism differences, and the four grasses outcompeted alfalfa in the intercropping treatments. The two intercropping mixtures alfalfa/triticale and alfalfa/oat had the best overall performance.

Key words: intercropping pattern, minirhizotron, root characteristics, carbon metabolism, nitrogen metabolism