[Characteristics of Cadmium Concentration and Transport of Pueraria thornsonii in Farmland with Different Cadmium Pollution Degrees].

This study aimed to elucidate the cadmium (Cd) concentration and transport characteristics of Pueraria thornsonii in farmland with different Cd pollution degrees, so as to provide a reference basis for phytoremediation of Cd-contaminated farmland. The multi-point experiments in farmland with different Cd pollution degrees[ω(Cd) 0.32-38.08 mg·kg-1] were conducted, and the biomass (dry weight), Cd content, accumulation, concentration, and transport of Cd in P. thornsonii tissues under the main growing period were assessed. According to the results, for P. thornsonii, the tuber dry weight ranged from 5.04 to 11.98 t·hm-2, biomass ranged from 13.21 to 29.07 t·hm-2, and Cd accumulation ranged from 15.74 to 106.03 g·hm-2in the study area. The pattern of Cd uptake by P. thornsonii showed that the main vine>leaf>lateral branches>basal part of sti>tuber. The Cd content in P. thornsonii tissues considerably increased with soil Cd content (P<0.05), whereas the biomass decreased significantly (P<0.05). The Cd concentration and transport factor of aboveground parts in P. thornsonii showed a trend of initially falling, then increasing and decreasing again, whereas the Cd enrichment and transport coefficient of tubers gradually decreased. Correlation analysis revealed that the amount of Cd in the soil was a major predictor of Cd accumulation in P. thornsonii. Under light to moderate Cd contamination, the commercial portion of P. thornsonii (arrowroot)[ω(Cd) 0.03-0.22 mg·kg-1] was less than the standard limit for medicinal plants (≤ 0.30 mg·kg-1). In P. thornsonii from moderately contaminated areas, the Cd concentration and transport factor of aboveground parts were 2.43-7.97 and 3.02-9.81, respectively. This indicates that P. thornsonii is a prospective plant ideal for remediating Cd-contaminated soil because of its high capacity to transfer and enrich Cd.

Effect of biochar with different particle sizes on the sorption-desorption characteristics of soil phosphorus.

The size of particles determines the adsorption reaction. In this study, three different particle sizes of biochar (0.25-1 mm, 0.075-0.25 mm, <0.075 mm) were produced from rapeseed straw (SBC) and chicken manure (MBC). The biochar was mixed with high phosphorus (P) soil and low P soil and then incubated for 30 days. We conducted isothermal P sorption and desorption experiments to evaluate the effects of biochar particle size on sorption-desorption characteristics of soil P, and analyzed soil properties associated with P sorption. The results showed that P sorption capacity of SBC and MBC in the water system was highest for the smallest particle size (<0.075 mm) (SBC: 43125 mg·kg-1, MBC: 20083 mg·kg-1), followed by the intermediate particle size (0.075-0.25 mm) (SBC: 37376 mg·kg-1, MBC: 13199 mg·kg-1) and the largest particle size (0.25-1 mm) (SBC: 27749 mg·kg-1, MBC: 12251 mg·kg-1). However, there was little difference in soil P sorption between the three particle sizes of the same biochar in the soil system. In comparison with no biochar treatment, the addition of SBC increased the Langmuir P sorption maximum (Smax) by 236.8%-755.7%, and decreased soil P desorption rate. The addition of MBC increased Smax, but the enhancement was less than that of SBC. Soil P desorption rate was increased by 7.2%-295.9%. Both SBC and MBC significantly increased the contents of soil total P, available P, and exchangeable calcium (Ca) and magnesium (Mg). The increases in Ca and Mg contents due to biochar addition was 64.0%-257.1% (SBC) and 39.1%-205.3% (MBC), respectively. The contents of soil exchangeable Ca and Mg were positively correlated with Smax. These results suggested that biochar particle size had little effect on soil P sorption, but the enrichment of Ca and Mg due to biochar addition played a critical role in regulating soil P sorption. The rapeseed straw biochar had a high adsorption capacity for soil P, making it suitable for improving the P fixation capacity of soil rich in P and reducing the loss of excess P. Chicken manure biochar could be used to improve the P availability of low P soils and increase the contents of available P.