Biochar and Glomus caledonium Influence Cd Accumulation of Upland Kangkong ( Ipomoea aquatica Forsk.) Intercropped with Alfred Stonecrop ( Sedum alfredii Hance)

Both biochar application and mycorrhizal inoculation have been proposed to improve plant growth and alter bioaccumulation of toxic metals. A greenhouse pot trial was conducted to investigate growth and Cd accumulation of upland kangkong (Ipomoea aquatica Forsk.) intercropped with Alfred stonecrop (Sedum alfredii Hance) in a Cd-contaminated soil inoculated with Glomus caledonium and/or applied with biochar. Compared with the monocultural control, intercropping with stonecrop (IS) decreased kangkong Cd acquisition via rhizosphere competition, and also decreased kangkong yield. Gc inoculation (+M) accelerated growth and Cd acquisition of stonecrop, and hence resulted in further decreases in kangkong Cd acquisition. Regardless of IS and +M, biochar addition (+B) increased kangkong yield via elevating soil available P, and decreased soil Cd phytoavailability and kangkong Cd concentration via increasing soil pH. Compared with the control, the treatment of IS + M + B had a substantially higher kangkong yield (+25.5%) with a lower Cd concentration (−62.7%). Gc generated additive effects on soil alkalinization and Cd stabilization to biochar, causing lower DTPA-extractable (phytoavailable) Cd concentrations and post-harvest transfer risks.