Arbuscular mycorrhizal fungi induce differential Cd and P acquisition by Alfred stonecrop (Sedum alfredii Hance) and upland kangkong (Ipomoea aquatica Forsk.) in an intercropping system

A greenhouse pot experiment was conducted to study cadmium (Cd) and phosphorous (P) acquisition of upland kangkong (Ipomoea aquatica Forsk.) intercropped with Alfred stonecrop (Sedum alfredii Hance) in a Cd-contaminated soil inoculated with arbuscular mycorrhizal (AM) fungi. There were four treatments, including monoculture of kangkong (control), intercropping with stonecrop (IS), and intercropping with stonecrop plus inoculation with Glomus caledonium (IS + Gc) or Glomus versiforme (IS + Gv). Both kangkong and stonecrop plants were harvested at week 8 after seeding or cutting. Compared with the control, IS tended to decrease Cd and P acquisition by neighboring kangkong via competition for phytoavailable Cd and P. The inoculation of Gc, but not Gv, significantly elevated Cd acquisition by stonecrop, and hence resulted in significantly lower Cd acquisition by kangkong and the subsequent Cd concentrations in both roots and shoots of kangkong. Both Gc and Gv significantly increased mycorrhizal colonization rates in stonecrop roots, as well as acid phosphatase activities and available P concentrations in the soil. However, only Gc significantly elevated P acquisition and shoot biomass of the host plant (stonecrop), while Gv significantly increased P acquisition and shoot biomass of neighboring kangkong rather than of stonecrop, causing a significant dilution effect on kangkong shoot Cd concentration. In addition, both Gc and Gv inoculation significantly decreased soil DTPA-extractable (phytoavailable) Cd concentrations by elevating soil pH. The results showed that Gc and Gv played totally different roles in the intercropping system for vegetable production and phytoremediation of Cd-contaminated soils.