Several studies have shown that intercropping can contribute to increased phosphorus (P) uptake by plants resulting in higher yields and improved grain nutritional quality. However, the underlying mechanisms of increased plant P acquisition are not yet fully understood. Potential mechanisms leading to increased P acquisition are (i) increased phosphatase activity in the rhizosphere of companion plants that is beneficial for the main culture plant, (ii) high proton and organic acid exudation of the companion plant that mobilize otherwise-unavailable forms of P, (iii) niche complementarity of the roots, and (iv) shifts in the microbial community induced by the companion plant that are beneficial for the main culture.
The aim of this study was to test these potential mechanisms of P acquisition in an intercropping experiment. We investigated root architecture as well as pH changes and phosphatase activity in the rhizosphere of maize (Zea mays) intercropped with either faba bean (Vicia faba), soybean (Glycine max), blue lupin (Lupinus angustifolius) or white mustard (Sinapis alba) in comparison to monoculture. For this purpose, plants were grown in rhizoboxes with an inner size of 29 x 49 x 3 cm that were inclined by 50° to make the roots grow at the bottom wall of the rhizobox, which could be opened. Phosphatase activities were investigated by soil zymography, and pH changes were assessed using pH-indicator gels.
First results suggest that different plant types use different P acquisition mechanisms. White mustard alkalized its rhizosphere, faba bean acidified its rhizosphere, and blue lupin exuded high amounts of phosphatases. Further analyses are still outstanding.