Effects of Vegetation Restoration on Soil Enzyme Activity in Copper and Coal Mining Areas

Accumulation and risk assessment of mercury in soil as influenced by mercury mining/smelting in Tongren, Southwest China

To investigate the influence of mercury (Hg) mining/smelting on the surrounding soil environment, ninety soil samples were collected around Hg mining/smelting areas in Tongren city, Guizhou Province, Southwest China. The total mercury (THg), methylmercury (MeHg), bioavailability and fractions of Hg in the soil and their potential risk were evaluated. The results showed that Hg mining/smelting significantly increased the soil pH and decreased the soil organic matter content (p < 0.05). The THg content in the surrounding soil was much higher than that at the control site, with almost all the samples exceeding the national standard in China (3.4 mg/kg, GB15618-2018). Similarly, the concentrations of MeHg (0.09-2.74 μg/kg) and bioavailable Hg (0.64-62.94 μg/kg) in these soil samples were also significantly higher than those in the control site. However, the MeHg/THg ratio was significantly lower in mining/smelting influenced soils (0.01-0.68%) than in control soils (0.60-3.72%). Fraction analysis revealed that residual (RES-Hg) and organic matter-bounded (OM-Hg) Hg accounted for more than 50% of the THg. Ecological risk assessment revealed that the potential ecological risk for most of the Hg mining/smelting-influenced soils (30.16 ≤ Er ≤ 2280.02) were higher than those at the control site (15.12 ≤ Er ≤ 27.1). In addition, these Hg mining/smelting-influenced soils posed acceptable noncarcinogenic risks to adults (except for two soil samples), with hazard indices (HIs) ranging from 0.04 to 1.11 and a mean HI of 0.44. However, children suffer serious noncarcinogenic risks, with HIs ranging from 0.34 to 7.43 and a mean HI of 3.10.

Effects of vegetation restoration on the concentrations of multiple metal elements in post-mining soils

Vegetation restoration is vital for soil ecological restoration in post-mining areas, but a global-scale quantitative assessment of its effects on soil metal elements is lacking. Here, we conducted a meta-analysis with 2308 paired observations collected from 137 publications to evaluate vegetation restoration effects on the concentrations of 17 metal elements, namely K, AK (available K), Ca, Na, Mg, Fe, Mn, Zn, Cu, Al, Cr, Co, Ni, Cd, Sb, Hg, and Pb in post-mining soils. We found that (1) vegetation restoration significantly increased the concentrations of K, AK, Ca, Mg and Co by 43.2, 42.5, 53.4, 53.7, and 137.2%, respectively, but did not affect the concentrations of Na, Fe, Mn, Zn, Cu, Al, Cr, Ni, Cd, Sb, Hg, and Pb; (2) the effects of vegetation restoration on soil metal concentration were seldom impacted by vegetation type, while soil depth only affected the responses of AK, Cd, and Pb concentrations to vegetation restoration, and leaf type only impacted the responses of Ca and Ni concentrations to vegetation restoration; (3) latitude, elevation, restoration year, climate, and initial soil properties were also important moderator variables of vegetation restoration effects, but their impacts varied among different metals. Overall, our results clearly showed that vegetation restoration in posting-mining areas generally have a positive effect on the concentrations of nutrient elements but did not influence that of toxic elements, which provides useful information for the restoration and reconstruction of soil ecosystem in post-mining areas.

Assessment of CuO NPs on soil microbial community structure based on phospholipid fatty acid techniques and phytotoxicity of bok choy seedlings

In this study, a soil culture and a hydroponic experiment were conducted to assess the toxicology effects of copper oxide nanoparticles (CuO NPs) on soil microbial community structure and the growth of bok choy. Results showed CuO NPs had an inhibitory effect on soil microbial abundance, diversity, and activity, as well as the bok choy seedling growth, whereas CuO NPs at low concentrations did not significantly affect the soil microbial biomass or plant growth. In soil, CuO NPs at high dose (80 mg kg^-1) significantly reduced the indexes of Simpson diversity, Shannon-Wiener diversity and Pielou evenness by 3.7%, 4.9% and 4.5%, respectively. In addition, CuO NPs at 20 and 80 mg kg^-1 treatment significantly reduced soil enzymes (urease, alkaline phosphatase, dehydrogenase, and catalase) activities by 25.5%-58.9%. Further, CuO NPs at 20 mg L^-1 significantly inhibited the growth of plant root by 33.8%, and catalase (CAT) activity by 17.9% in bok choy seedlings. The present study can provide a basis for a comprehensive evaluation of the toxicity effect of CuO NPs on soil microorganisms and phytotoxicity to bok choy seedlings.

Effect of yeast application on soil health and root metabolic status of corn seedlings under drought stress

The soil enzymes are the heart of the biochemical reactions that occur in the soil saving the soil nutrients needed for plant growth. Recently yeast's importance as plant growth-promoting microorganisms has great attention. This study evaluated the effect of yeast application on the soil enzymes activity and root metabolic status in corn plants under drought stress. A pot experiment was performed. The pots were divided into two groups; the first group was used for yeast application, the other group was used as a non-treated group. Each group was subdivided into two groups according to water treatment. One is 75%; the other is 45% of field capacity. Soil and root samples were taken at 5, 10, and 15 days after drought application for analysis. Soil samples were subjected to NPK and soil enzymes activity analysis. The root samples were subjected to determination NPK content, the osmolytes, lipid peroxidation, and antioxidant enzymes. The present results showed that yeast application upregulated the soil enzymes under drought which protected the NPK content in the soil. Therefore NPK in the treated group was significantly higher than that in the non-treated group. Also, yeast application improved the roots' osmotic status, the treated group showed significant osmolytes accumulation. Besides that the antioxidant enzymes activity status in the treated group was significantly higher than that in the non-treated group which significantly decreased the lipid peroxidation in the treated group. Yeast application can be an effective promising tool for improving the corn plant tolerance against drought stress.