Intercropping of Pinellia ternata (herbal plant) with Sedum alfredii (Cd-hyperaccumulator) to reduce soil cadmium (Cd) absorption and improve yield

Soil contamination by cadmium (Cd) is of global concern, threatening not only crop production, but also supply of herbal medicine. Research studies usually grow crops with Sedum alfredii (a Cd-hyperaccumulator). However, intercropping herbal plants with S. alfredii and their interactions with hydro-chemical properties of soil are rarely considered. This study examines the growth of a herbal plant, Pinellia ternata, intercropped with S. alfredii in Cd-contaminated soil. Plant characteristics were assessed, especially biomass and Cd content of bulbil (yield and quality of P. ternata). Soil hydro-chemical properties including water retention, Cd content and organic matter were determined with statistical analyses. At low soil-Cd contamination (0.6 μg/g), bulbil biomass of intercropped P. ternata (PSL) was almost double compared with monoculture of P. ternata (PL), which is barely significant (p ≈ 0.05). The corm biomass of PSL was also significantly greater than that of PL (p < 0.05). Although soil-Cd contamination became more severe by increasing to 3 μg/g, the bulbil biomass in the intercrop was not significantly different from PL (p > 0.05). That said, it is evidenced that the yield of intercropped P. ternata was improved in Cd-contaminated soil. Such improvement was mainly attributed to reduced soil-Cd content and enhanced soil-water retention which was governed by plant roots and soil organic matters. The soil-water retention was first identified as a critical parameter in promoting plant growth under intercropping. More importantly, the bulbil-Cd content of P. ternata in PSL was significantly reduced (p < 0.05). This study demonstrates that the newly proposed intercrop is feasible to improve yield of herbal plants, and at the same time reduce heavy metal absorption and accumulation in medicinal organs, especially for P. ternata. This is anticipated to reduce the human health risk imposed by ingestion of Chinese herbal plants.