Alkaline humic acid fertilizer alters the distribution, availability, and translocation of cadmium and zinc in the acidic soil-Sauropus androgynus system.

Humic acids (HA) are a popular soil additive to reduce metal availability, but they have the drawbacks of reduced effectiveness over time and a significant reduction in soil pH. An alkaline humic acid fertilizer (AHAF) combining alkaline additives with HA was developed to overcome such drawbacks. A field experiment was conducted to investigate the effects of different AHAF application rates on the physicochemical properties, bioavailability, accumulation, and translocation of Cd and Zn heavy metals in Sauropus androgynus grown in acidic soil. Based on our results, the 100AF (100% AHAF) treatment significantly increased soil pH, cation exchange capacity (CEC), and organic matter content (OM) after one year of application. Compared with the control treatment (CK), the application of different rates of AHAF resulted in a 37.1-40.3% decrease in soil exchangeable Cd fractions (Exc-Cd) and an increase in the humic acid-bound Cd fractions (HA-Cd) Fe- and Mn-oxide-bound Cd fractions (OX-Cd), and organic matter-bound Cd fractions (OM-Cd) by 9.5-64.6%, 24.8-45.1%, and 158.8-191.2%, respectively (P < 0.05). The different AHAF treatments decreased the Res-Zn, Exc-Zn, and OM-Zn fractions by 69.6-73.0%, 7.4-23.9%, and 18.1-23.2%, respectively (P < 0.05), and increased the HA-Zn fraction by 8.4-28.1%. In the control treatment, the bioconcentration factors (BCFs) for Cd and Zn in different S. androgynus plant organs were in the following order: (Cd) Leaves > Stems > Branches > Roots > Edible branches; (Zn) Roots > Stems > Leaves > Branches > Edible branches. The transfer factors (TFs) of Cd and Zn in S. androgynus were classified as follows: TF2 > TF1 > TF3 > TF4. Thus, S. androgynus stems, and roots had a strong ability to transport Cd and Zn to the leaves. Compared with CK, the 100AF treatment significantly increased the BCFs for Zn in all plant parts (except BCFedible branches). In contrast, it significantly decreased all BCFs and TFs for Cd and the TF4 for Zn, effectively reducing Cd and Zn accumulation in the edible branches of S. androgynus. Soil pH, CEC, OM, and HA-M fraction were highly and significantly negatively correlated with Cd and Zn content in edible branches (P < 0.001). Stepwise multiple linear regression analysis revealed that the soil HA-M fraction was the key contributing factor for Zn accumulation and translocation in S. androgynus. Moreover, based on our findings, the absorption, uptake, and translocation of Cd and Zn were mainly determined by metal speciation and the pH in the soil. Moreover, the competitive antagonistic mechanisms between Zn and Cd absorption also affected their accumulation in S. androgynus. Thus, AHAF can be used as a soil amendment to sustainably improve acidic soils and effectively reduce Cd and Zn accumulation in edible branches of S. androgynus.

Physicochemical properties, multi-elemental composition, and antioxidant activity of five unifloral honeys from Apis cerana cerana.

Honey quality is in relation to botanical origin, and physicochemical properties, elemental composition, and antioxidant activity have been used for assessment and identification of honeys. The goal of this study is to contribute to the general analysis of five unifloral honeys from Cocos nucifera L., Dalbergia benthami Prain, Bombax ceiba L., Castanea mollissima Bl., and mangrove in Hainan province, China. Our results revealed that B. ceiba honey had the highest pH (4.27), color (139.33 mm Pfund), ash content (1.03 g/100 g), and electrical conductivity (1312.00 µS/cm) in five unifloral honeys. Furthermore, B. ceiba honey also contained the highest levels of total phenolic content (75.54 mg GAE/100 g) and total flavonoid content (29.22 mg RE/100 g), as well as the strongest antioxidant activity (DPPH IC50 value, 3.97 mg/mL; FRAP value, 6527.43 µmol TE/kg). Moreover, we revealed a considerable variation in element contents in honeys using ICP-MS, with potassium being the most predominant element. B. ceiba honey had the highest contents of K, Ca, Mg, and P, whereas the highest amount of Na was found in mangrove honey. Overall, our data indicated that B. ceiba honey deserves further research as a potential antioxidant agent.