Soil amendments inhibited the cadmium accumulation in Ligusticum striatum DC. and improved the plant growth

Soil aggregates display a significant influence on the bioavailability of heavy metals in soil. In this study, we conducted a field experiment in the main producing area of Ligusticum striatum DC. to explore the effects of the amendments on cadmium (Cd) distribution in soil aggregates and plant growth. L. striatum was planted in natural Cd-polluted soils added with mixed amendments, composed of heavy/light calcium carbonate (Type 1/Type 2 amendments), calcium-bentonite, potassium dihydrogen phosphate, biochar, sodium silicate, and attapulgite, with the application rate of 0.5 t ha−1, 1.5 t ha−1, and 5.0 t ha−1. The results demonstrated that the application of the amendments promoted the formation of soil macroaggregates (250–2000 μm and >2000 μm) and, altered soil Cd distribution among aggregates fractions by translocating Cd from macroaggregates into small one (microaggregate; <250 μm). Soil amendments addition greatly alleviated the phytotoxic effects of Cd on plants and promoted the biomass of the rhizome of L. striatum by 14.38−53.47%. Based on the structural equation modeling, the decrease of available Cd in the fraction of large macroaggregates greatly contributed to the less accumulation of Cd in plants (r = 0.70; p < 0.05). In general, the amendments inhibited the plant Cd accumulation by re-distribution of Cd among soil aggregates and, improved the plant growth by supplying available nutrients.