Arbuscular mycorrhizal fungi induced differential Cd and P phytoavailability via intercropping of upland kangkong (Ipomoea aquatica Forsk.) with Alfred stonecrop (Sedum alfredii Hance): Post-harvest study

A post-harvest experiment was conducted further to our previous greenhouse pot study on upland kangkong (Ipomoea aquatica Forsk.) and Alfred stonecrop (Sedum alfredii Hance) intercropping system in Cd-contaminated soil inoculated with arbuscular mycorrhizal (AM) fungi. Previously, four treatments were established in the intercropping experiment, including monoculture of kangkong (control), intercropping with stonecrop (IS), and IS plus inoculation with Glomus caledonium (IS + Gc) or Glomus versiforme (IS + Gv). Both kangkong and stonecrop plants were harvested after growing for 8 weeks. Then, the tested soils were reclaimed for growing post-harvest kangkong for 6 weeks. In the post-harvest experiment, there were no significant differences between the IS and control treatments, except for a significantly decreased (p < 0.05) soil available P concentration with IS treatment. Compared with IS, both IS + Gc and IS + Gv significantly decreased (p < 0.05) soil DTPA-extractable (phytoavailable) Cd concentrations, but not total Cd, by elevating soil pH, causing significantly lower (p < 0.05) Cd concentrations in both the root and shoot of kangkong. In addition, both Gc and Gv significantly increased (p < 0.05) soil acid phosphatase activities and available P concentrations and hence resulted in significantly higher (p < 0.05) plant P acquisitions. However, only Gv significantly increased (p < 0.05) kangkong yield, while Gc only significantly elevated (p < 0.05) the shoot P concentration. It suggested that AM fungi have played key roles in Cd stabilization and P mobilization in the intercropping system, and such positive responses seemed to be sustainable and valuable in post-harvest soils.