Herbal medicine is gaining more popularity due to its wide ranging medical functions. Harvesting natural resource of herbal plants is insufficient to fulfill the demand. An example is the bulbil of Pinellia ternata P. ternata), ranked 22 in the list of Chinese herbal plants adopted for Chinese prescription. Thus, large scale cultivation is required. However, limited investigations for growing P. ternata cause misuse of nutrient. This inhibits plant growth and further contaminates soil with cadmium (Cd) which also toxifies P. ternata. Recently, hydrated biopolymers have been regarded as sustainable soil conditioners for vegetation. But, studies on the soil-biopolymer interaction and even using biopolymers for the growth of P. ternata are rare.

In this study, the effects of nitrogen (N),...[ Read more ]

Herbal medicine is gaining more popularity due to its wide ranging medical functions. Harvesting natural resource of herbal plants is insufficient to fulfill the demand. An example is the bulbil of Pinellia ternata P. ternata), ranked 22 in the list of Chinese herbal plants adopted for Chinese prescription. Thus, large scale cultivation is required. However, limited investigations for growing P. ternata cause misuse of nutrient. This inhibits plant growth and further contaminates soil with cadmium (Cd) which also toxifies P. ternata. Recently, hydrated biopolymers have been regarded as sustainable soil conditioners for vegetation. But, studies on the soil-biopolymer interaction and even using biopolymers for the growth of P. ternata are rare.

In this study, the effects of nitrogen (N), phosphorus (P), potassium (K) and their combinations on the growth of P. ternata were first investigated. Then, a Cd-hyperaccumulator, called Sedum alfredit (S. alfredii), was newly proposed to cultivate with P. ternata at low and high Cd concentrations. Subsequently, the water retention, wettability and intrinsic air permeability of the soil with various biopolymer types were determined. Finally, the soil was added with biopolymers for the growth of P. ternata. Laboratory pot tests were performed to measure the plant characteristics, soil matric suction and water content for assessing the growth of P. ternata. Nutrients in the soil and a common active ingredient (i.e. succinic acid) of P. ternata were examined. In addition, the total Cd content in the soil and the bulbil of P. ternata was measured.

Among the test conditions with a single nutrient, P gave the highest yield for P. ternata (i.e. bulbil biomass). When multiple nutrients were added, the nutrients accumulated on the top soil. This increased osmotic suction and reduced the soil-water retention so the water uptake by the plants decreased. Due to better root development, the yield of P. ternata in the condition with a mixture of P and K was the highest. Statistical analysis also showed that the yield was strongly correlated with soil P content and root biomass (r>0.7). It suggested that P governs the yield of P. ternata. Moreover, the succinic acid in the bulbil was strongly correlated to soil N content (r≈0.7). This implies that the N concentration is a key to improve the active ingredient of P. ternata.

After S. alfredii was planted with P. ternata, the growth of P. ternata was enhanced in soil with low Cd concentration while it was suppressed at high Cd concentration. For low Cd concentration, the presence of S. alfredii increased the soil-water retention and reduced the total Cd content in the soil. This in turn increased the yield of P. ternata by 50% and reduced the Cd content in the bulbil by 10%. Growing S. alfredi with P. ternata in the soil with low Cd concentration improved the yield of P. ternata and reduced the Cd content of P. ternata.

When the soil was conditioned by biopolymers, the yield of P. ternata was reduced due to a high soil-water content. This caused water-logging and reduced the oxygen availability in the soil, as supported by the results from soil-biopolymer interaction. Although biopolymers increased the soil-water retention, the air permeability of the soil was always reduced by biopolymers. The max reduction of the air permeability of the soil reached up to two orders of magnitude. It is important to consider the air permeability of the soil when biopolymers are adopted for plant growth.