Legume cultivars affect N uptake, component crop growth, and soil physical and chemical characteristics in maize–legume intercropping systems.  However, how belowground interactions mediate root growth, N fixation, and nodulation of different legumes to affect N uptake is still unclear.  Hence, a two-year experiment was conducted with five planting patterns, i.e., maize–soybean strip intercropping (IMS), maize–peanut strip intercropping (IMP), and corresponding monocultures (monoculture maize (MM), monoculture soybean (MS), and monoculture peanut (MP)), and two N application rates, i.e., no N fertilizer (N–) and conventional N fertilizer (N+), to examine relationships between N uptake and root distribution of crops, legume nodulation and soil N availability.  Results showed that the averaged N uptake per unit area of intercrops was significantly lower than the corresponding monocultures.  Compared with the monoculture system, the N uptake of the intercropping systems increased by 31.7–45.4% in IMS and by 7.4–12.2% in IMP, respectively.  The N uptake per plant of intercropped maize and soybean significantly increased by 61.6 and 31.8%, and that of intercropped peanuts significantly decreased by 46.6% compared with the corresponding monocultures.  Maize and soybean showed asymmetrical distribution of roots in strip intercropping systems.  The root length density (RLD) and root surface area density (RSAD) of intercropped maize and soybean were significantly greater than that of the corresponding monocultures.  The roots of intercropped peanuts were confined, which resulted in decreased RLD and RSAD compared with the monoculture.  The nodule number and nodule fresh weight of soybean were significantly greater in IMS than in MS, and those of peanut were significantly lower in IMP than in MP.  The soil protease, urease, and nitrate reductase activities of maize and soybean were significantly greater in IMS and IMP than in the corresponding monoculture, while the enzyme activities of peanut were significantly lower in IMP than in MP.  The soil available N of maize and soybean was significantly greater increased in IMS and IMP than in the corresponding monocultures, while that of IMP was significantly lower than in MP.  In summary, the IMS system was more beneficial to N uptake than the IMP system.  The intercropping of maize and legumes can promote the N uptake of maize, thus reducing the need for N application and improving agricultural sustainability.

   Drought is a major abiotic factor limiting agricultural crop production. The objective of this study was to investigate whether α-naphthaleneacetic acid (NAA) confers drought tolerance to soybeans and if such tolerance is correlated with the early reactive oxygen species (ROS) accumulation in leaves. The plants of soybean (Glycine max [L.] Merr.) cv. Nannong 99-6 and cv. Kefeng 1 were foliar treated with 40 mg L⁻¹ NAA at the beginning of bloom and then exposed to water stress for 10 d. We monitored changes in ROS levels, lipid peroxidation and antioxidant system as well as plant biomass during the drought treatment. The results showed that drought stress significantly depressed the growth and yield regardless of spraying NAA. However, drought-stressed plants treated with NAA showed much higher plant biomass and yield than those without NAA. The ROS levels increased in stressed Kefeng 1 but not in stressed Nannong 99-6 2–4 days after the treatment (DAT). During 6–10 DAT, stressed Kefeng 1 had greater increase in the levels of superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), γ-glutamylcysteine synthetase (γ-GCS), reduced ascorbate (AsA), and glutathione (GSH), smaller increase in ROS and malondialdehyde (MDA) as compared with stressed Nannong 99-6. Low ROS prevented ROS from directly reacting with membrane lipid during this stage and, consequently, reduced the cell damage. NAA application elevated ROS levels at 4 DAT, and then increased antioxidant capacity and blocked the increase in the MDA and ROS in stressed Nannong 99-6 and Kefeng 1. Overall, the results indicate that NAA application effectively alleviates the adverse effects of drought stress, which is partially attributable to increase in antioxidant ability and decrease in lipid peroxidation induced by the early ROS accumulation triggered by NAA.