| In recent years, gap between crop production and food demands were enlarging, and it became more and more important to raise crop productivity in order to meet the increasing food requirements of an increasing population, with decreasing water and land resources. Intercropping could use resources more effectively and had higher productivity, compared to sole crops. Phosphorus was a kind of unrenewable resources, and very limited in the world. Previous studies showed that P was utilized by intercropping more efficiently than sole cropping systems. However, the mechanism behind it was not clear. So hydroponic culture, technique of different root barriers and paper liter culture were carried out to study the organic acids and proton efflux of roots of faba bean, soybean and maize to illuminate the mechanism of interspecific facilitation on P uptake in fababean/maize and soybean/maize intercropping systems. The objective of the research work was to give scientific evidences for improving productivity and efficient P utilization in intercropping system and give the strong guarantee for agricultural sustainable development. The following results were obtained in experiments.1. In a pot experiment with hydroponic culture, the amount of organic acid exudates from roots was considerably different between faba bean, soybean and maize. Large amounts of tartaric and succinic were exuded from faba bean roots. Total amounts of organic acid exudation of faba bean was 70.8 and 28.5 times as much as that from soybean roots under 9 days and 15days, respectively, and 65.6 and 28.5 times as much as that from maize roots. There was no difference between three plants in soil condition.2. Organic acid exudation for all three species was not affected by P supply level in both pot experiments with hydroponic or soil culture. In hydroponic culture, the total amounts of organic acid in faba bean/maize intercropping was significantly higher than soybean/maize intercropping at 9 days of P deficiency; there was no significant difference between two intercropping patterns under 15 days of P deficiency.3. Faba bean had strong ability of rhizosphere acidification. At very early growth stage, plants were grown in half concentration of full nutrient solution, which supplied with 0.1mM L-1 P, the pH of nutrient solution grown faba bean only for four days was decreased to 4.4. Under P deficiency, the pH of the nutrient solution grown faba bean was lower than initial 6.0 during the whole cultivated growth states, and stabilized 4.0-4.5 from day 4 to day 19. In visualization of rhizosphere acidification, faba bean rhizosphere turned bright yellow, and the amount of proton efflux of the faba bean was significantly greater than soybean and maize.4. In hydroponic culture, the pH of the solution grown soybean was always higher than initial 6.0 of new nutrient solution, even under P deficiency condition. In visualization of rhizosphere acidification, soybean presented a rhizosphere acidification too, but was much less than faba bean. Furthermore, soybean seems to alkalize its rhizosphere in root tips whatever P was supplied or not. In contrast, the whole roots of maize alkalized the rhizosphere in both monoculture and intercropping, regardless supplying with P or not. In hydroponic culture, the pH in the solution grown maize was declined onlyafter P deficiency for 13 days.5. In hydroponic culture, the pH of nutrient solution grown faba bean and maize together in the same pot (intercropping of faba bean and maize) was lower than that of intercropping of soybean and maize during early (about 13 days) growth stage, regardless of P supply or not.
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