Mechanism Of Interspecific Facilitation On Phosphorus Uptake By Crops In Intercropping Systems

Intercropping, a commonly used agronomic practice by farmers in China for a long time, can use nutrient and water resources efficiently and enhance crop yield enormously. Phosphorus is a kind of unrenewable resource and second only to N as the most limiting element for plant growth all over the world. Phosphorus use efficiency can be improved by selecting suitable crop intercropped. Therefore, intercropping plays an important role in solving contradicts between ever increasing population and deteriorate ecological environment due to shortage of resources, and attracts more and more agronomists and ecologists attention. So hydroponic culture and technique of different root barriers were carried out to study the mechanism of interspecific facilitation on P uptake by crops from organic phosphorus and sparingly soluble phosphorus forms in soils in maize/chickpea and maize/faba bean intercropping systems based on observation of field experiments. The objective of the research work was to give scientific evidences for improving productivity and higher efficient resource utilization in intercropping system. The following results were obtained in the experiments.The ability of chickpea and faba bean supplied with phytate to mobilize organic P were stronger than maize in maize/chickpea and maize/faba bean intercropping systems. The biomass of maize intercropped with chickpea or without root barriers was significantly higher than that of monoculture one or with solid barrier in hydroponic culture or soil culture. Chickpea facilitated phosphorus uptake by associated maize from an organic P source. Total P uptake in maize/chickpea and maize/faba bean intercropping systems was significantly higher than that of monoculture. In hydroponic culture total P uptake from organic P source by intercropped maize was increased by 116.7% over monoculture and total P uptake by monoculture chickpea was decreased by 14.7% compared to monoculture one. In soil culture, P uptake by maize and P concentration in maize shoots was greater 118.0%, 43.7% 28.1% and 10.2% with mesh barrier and with no barrier than with solid barrier, respectively. Acid phosphatase secreted by chickpea and maize and soil acid phosphatase activity in the rhizosphere of maize and chickpea were significantly increased due to P deficiency and phytate supplied. Acid phosphatase activities of chickpea were higher than those of maize and played important role in P uptake from an organic P source in maize/chickpea intercropping system.In sterilized soil condition, total P uptake in maize/faba bean intercropping was significantly higher than monoculture supplied with organic P. Mycorrhizal fungus didn't play significant effects on interspecific facilitation for phosphorus uptake, and the facilitation was due to the interspecific root interaction. But phosphorus uptake by maize and faba bean inoculated with AM fungus was 2.38 and 1.82 as much as to the control because acid phosphatase activity and alkaline activity in the rhizosphere of maize and faba bean inoculated with AM fungus increased. Symmetrical effect on P uptake from organic P was observed when faba bean was dual inoculation with AM fungi and Rhizobium leguminosarum. Number of nodules, weight of nodules and mycorrhizal colonization of faba bean weresignificantly increased. At the same time the growth of associated maize was significantly facilitated indirectly due to improvement of nitrogen nutrition.The mechanism of better ability of faba bean in mobilizing sparingly soluble Fe-P and Al-P in maize/faba bean intercropping was conductive to acidify the rhizosphere soil and to be higher specific absorption rate of phosphorus. When Fe-P and Al-P were supplied phosphorus fertilizer recovery of faba bean was 4.13 and 1.03 times as much as that of maize, maize. Root length and specific P absorption rate of maize were significantly greater while rhizosphere pH was lower when roots of the two species grew together than when roots of the two species were separated, which lead to total P uptake by maize with...