Caragana microphylla, a native perennial leguminous shrub, is widely used for desertification control in China’s Horqin Sandy Land. We investigated the effects of afforestation using C. microphylla in areas with fixed and active dunes on soil carbon (C) and nitrogen (N) storage in the soil total and light-fraction (LF) organic matter. Compared to the values in the control areas, soil organic carbon (SOC) storage to a depth of 100 cm increased by 88%, 74%, and 145% at 9, 15, and 31 years after shrub planting, respectively; the corresponding values were 68%, 61%, and 195% for total nitrogen (TN) storage, 109%, 199%, and 202% for LF organic carbon storage, and 203%, 337%, and 342% for LF nitrogen storage. The soil light-fraction (LF) organic matter contributed significantly to total SOC and TN storage, despite the low proportion of total soil mass accounted for by the LF dry matter. Thus, afforestation using C. microphylla was an effective way to sequester C and to restore degraded soils, but the process was slow; it would take more than 100 years to fully restore SOC storage in active dunes through afforestation with C. microphylla in the Horqin Sandy Land.

Recently, the water quality of the second longest River in China (the Yellow river) is deteriorating severely. To investigate the heavy metals contaminated degrees, potential risks and pollution sources of heavy metals in the river, we measured the concentrations of 8 heavy metals (Fe, Mn, Cu, Ni, Zn, Cr, Pb and Cd) from 122 surface sediment samples collected along the upstream Yellow River. According to the results of enrichment factor (EF) analysis and the geoaccumulation index (Igeo) evaluation, we found Cd accumulated significantly for moderately contaminated level and the other heavy metals existed at uncontaminated levels. We conducted risk assessment by using calculation of the sediment quality guidelines (TEC-PEC SQGs) and potential ecological risk index (RI), and the results implied that the concentrations of Ni, Cr and Cd had potential harm for aquatic organisms and the upstream Yellow River had integral no toxic. Moreover, the results of multivariate analysis (principle component analysis, hierarchical cluster analysis and correlation analysis) indicated that Fe, Mn, Cu, Zn, Cr and Cd in the river primarily originated from natural sources, while Ni and Pb mainly derived from different human activities. In addition, partial Cu and Cd come from anthropogenic sources of Ni discharge.

Biodegradable chelating agents and nitrogen (N) fertilizers are widely used for the remediation of heavy metal-contaminated soils due to their ability to promote plant growth, enhance metal mobility and facilitate plant uptake. In this study, a pot experiment was conducted to investigate the effects of nitrate nitrogen (N-NO₃⁻), ammonium nitrogen (N-NH₄⁺) and amide nitrogen (N-amide) with different concentrations of 25, 50 and 75 mg N·kg⁻¹ combined with (S,S)-ethylenediaminedisuccinic acid (EDDS) (1 mmol·L⁻¹) on growth, biomass and phytoextraction efficiency of Bidens. pilosa L. and the bioavailability of cadmiun (Cd) in 15 mg·kg⁻¹ Cd-contaminated soil. The results demonstrated that the application of 50 mg N·kg⁻¹ N-NO₃⁻ and EDDS not only promoted plant growth and increased biomass, it also changed Cd distribution between operational fractions, increased available Cd content in soil, thereby maximizing the Cd uptake, thus enhancing the Cd enrichment capability of B. pilosa L. This combination achieved the maximum phytoextraction efficiency of 12.12% and the maximum soil Cd removal of 12.38% across all treatments. The comprehensive score obtained using the membership function method also showed that the treatment with 50 mg N·kg⁻¹ N-NO₃⁻ and EDDS had the highest score. In conclusion, combination of 50 mg N·kg⁻¹ N-NO₃⁻ and EDDS resulted in the greatest biomass production, and highest phytoremediation efficiency, indicating that it has great potential for application in phytoremediation with B. pilosa L. in Cd-contaminated soil.

As an important bioactive signaling molecule, nitric oxide (NO) participates in the responses of plants to various environmental stresses. The aim of this study was to investigate the influence of exogenous NO on the growth and cadmium (Cd) accumulation of alfalfa (Medicago sativa) during early growth. The results showed that Cd significantly inhibited alfalfa seedling growth and induced membrane lipid peroxidation. Addition of sodium nitroprusside (SNP, as an NO donor) significantly promoted seedling growth and induced the mobilization of seed photosynthate reserves, leading to an increase in total soluble sugar (SS) and reducing sugar (RS) contents. Application of SNP mitigated membrane peroxidation damage caused by Cd stress by enhancing catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and peroxidase (POD) activities in order to eliminate reactive oxygen species (ROS), thereby improving Cd resistance and increasing Cd accumulation in alfalfa. This promoting effect of SNP depended on its concentration; the most optimal SNP concentration to promote the growth and Cd absorption of alfalfa under Cd stress was found to be 200 µM. The fresh weight (FW), dry weight (DW) and Cd accumulation of seedlings treated with 200 µM SNP increased significantly by 23.10%, 30.32% and 82.50%, respectively, on the fifth day, compared with the Cd-only treatment.