| Cereal-legume intercropping is a widely used agricultural practice with a significant advantage in yield increasing and in resource utilization, which has been considered as an important practice in the sustainable agriculture development. Rice(Oryza sative) and mungbean (Vigna radia ta L.) are important food crops in the world, especially in tropical and subtropical regions. Arbuscular mycorrhiza fungi (AMF) distribute widely in the environment, which are found in about 80% of the terrestrial plants. Significant roles of arbuscular mycorrhizal fungi have been obtained for the plant, for example, they can promote the absorption of phosphorus in roots, accelerate the growth of plants, protect the plant against disease. The fungi in return benefit from the supply of carbohydrates derived from plant leaf photosynthesis. Thus, propagula of AMF have been used as biological soil amendments in modern sustainable agriculture. However, the contribution of arbuscular mycorrhiza, the common existed mutualistic symbiosis between most of crop roots and mycorrhizal fungi, has not yet been fully understood in the intercropping system.To evaluate the contribution of AMF in rice and mungbean intercropping system, we inoculated AMF to intercropped rice and mungbean. By labeling 15N isotope, the interactions among AMF, rice and mungbean were conducted to test the hypothesis that AMF could improve the efficiency of biological N fixation by the legume plants, utilization of N and P and total plant yield for the two crops.1. Intercropping of rice(Oryza sativa var. Japonica Nipponbare) and mungbean (Vigna radia ta L. var. Chuanyuan) in sterilized medium was inoculated with Glomus caledonium, Acaulospora laevis and G. mosseae for both crops, and Rhizobium Leguminosarum for mungbean. It showed that all of the three AMF could result in forming of arbuscular mycorrhizal for both rice and mungbean. The inoculation rate was 12.5%-36.7% for rice and 54.8%-66.7% for mungbean. Meanwhile the promoting effect of different AMF on plant growth was varied considerably, but the infection rate、hyphal length and stimulating effect of different AMF isolates on plant growth were differed markedly, suggesting G. caledonium was the effective isolate.Inoculation AMF to the both intercropped crops increased the the acquisition of P by both crops and the leaf chlorophyll content and the growth of the mungbean very significantly. The soluble sugar content, soluble protein content in leaves of AMF-inoculated plants were also increased largely in comparison to that in untreated plant leaves. The improvement of rice and mungbean growth and physiological characters were resulted mainly from directly increased phosphorus acquisition by fungal tissues and subsequently promoting phosphorus content of inoculated plants.2. The effect of phosphate application on AMF colonization and inoculation biological response with G. caledonium in sterilized medium was evaluated by a pot experiment. The highest mycorrhizal colonization into rice was obtained in the treatment of 10 mg/kg P applied in the culture medium, while it was 20 mg/kg P for mungbean. There was no significant effect of AMF inoculation on the growth of rice/mungbean seedlings at low and middle levels of P-application (0-10 mg/kg P for rice,0-20 mg/kg P for mungbean). However, the high level of P (50 mg/kg P) inhibited AMF infection in both plant roots and alightly decreased the dry weight of inoculated rice in comparison with that non-inoculation rice. The total uptake of phosphorus, chlorophyll content in the leaves and the plant growth was imrproved and were related to the infection rate of AMF in the mungbean.3. Using the methods of plastic net and nylon membrane partition and tracing 15N transferring between the intercropped upland rice and mungbean, we assayed the contributions of inoculation with arbuscular mycorrhiza fungi (AMF), G. caledonium 90036, on nutrient acquisition and biomass yield of rice and mungbean. Treatments with separation of the whole root systems by a plastic net, with and without barrier of nylon membrane to allow penetration of the fungal hyphae were used in the intercropping system. The results demonstrated that intercropping with legume crops significantly improved the formation of arbuscular mycorrhiza, particularly in the upland rice roots. The improved inoculation of mycorrhiza by the intercropping increased total P uptake by 57% in rice, total P and N acquisition by 65% and 64% in mungbean, respectively, and 54% of nodulation in the mungbean. The percentage of total 15N transfer from mungbean to rice leaves was increased by 5.4-15.7% due to inoculation with AMF. In contrast, only 2.7% of transfer from rice to mungbean and no AMF effect were detected. It is concluded that cereal and legume crop intercropping could increase mycorrhizal innoculation, which in turn improves the nodulation, leading to N and P acquisition and N transfer in the legume.4. The effects of AMF G. caledonium on the intercropping system of rice and mungbean growth, physiological metabolism and drought resistance of rice/mungbean in pot culture under different water content were assessed. The results showed that water stress seriously repressed plant growth, but did not influence the growth and AMF infection of plants. The P and N uptake of plant could be enhanced andsubaequently improved plant water status. While the repression degree of water stress on plant growth was greatly reduced, many photosynthesis parameters of inoculated plants were obtained mainly through direct water uptake by fungal tissues and through the improvement of nutrition. The accumulation of soluble sugar decreased proline content and effectively adjusted permeation ability of cell indirectly, and promoted the drought resistance of rice/ mungbean plants.5. In a pot experiment, the effects of inoculation with thre different AMF strains on the stress of rice/mungbean were studied. Three AMF strains used are G. caledonium, A. laevis and G. mosseae and the plants were sampled at the 30,45,60 days after inoculation with AMF. The AMF treatments decreased the content of malondialdehyde(MDA) in the leaves, but significantly increased the concentrations of soluble protein, and the activity of superoxide dismutase(SOD), catalase(CAT), peroxidase (POD), phenylalanine ammonialyase(PAL) and polyphenol oxidase(PPO) in the leaves of AMF inoculated plants. It is concluded that the AMF inoculation decreased the degree of stresses of the intercropped rice/mungbean under water and nutrient deficient conditions.The present study demonstrate that inoculation of a screened AMF G. caledonium to the plants in cereal-legume intercopping system might be a novel approach to high-yield, environment-friendly and effective utilization of water and nutrient resources in agriculture production. |
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