Mulches assist degraded soil recovery via stimulating biogeochemical cycling: metagenomic analysis.

Soil degradation of urban greening has caused soil fertility loss and soil organic carbon depletion. Organic mulches are made from natural origin materials, and represent a cost-effective and environment-friendly remediation method for urban greening. To reveal the effects of organic mulch on soil physicochemical characteristics and fertility, we selected a site that was covered with organic mulch for 6 years and a nearby lawn-covered site. The results showed that soil organic matter, total nitrogen, and available phosphorus levels were improved, especially at a depth of 0-20 cm. The activities of cellulase, invertase, and dehydrogenase in soil covered with organic mulch were 17.46%, 78.98%, and 283.19% higher than those under lawn, respectively. The marker genes of fermentation, aerobic respiration, methanogenesis, and methane oxidation were also enriched in the soil under organic mulch. Nitrogen cycling was generally repressed by the organic mulch, but the assimilatory nitrate and nitrite reduction processes were enhanced. The activity of alkaline phosphatase was 12.63% higher in the mulch-covered soil, and functional genes involved in phosphorus cycling were also enriched. This study presents a comprehensive investigation of the influence of organic mulch on soil microbes and provides a deeper insight into the recovery strategy for soil degradation following urban greening. KEY POINTS: • Long-term cover with organic mulches assists soil recovery from degradation • Soil physical and chemical properties were changed by organic mulches • Organic mulches enhanced genes involved in microbially mediated C and P cycling • Soil organic matter was derived from decomposition of organic mulch and carbon fixation • N cycling was repressed by mulches, except for assimilatory NO2- and NO3- reductions.

Temporal hormetic response of soil microbes to cadmium: A metagenomic perspective.

The hormetic response of microbes to cadmium (Cd) is often observed in soil, but the mechanisms are unclear. In this study, we proposed a novel perspective of hormesis that successfully explained the temporal hermetic response of soil enzymes and microbes, and the variation of soil physicochemical properties. Several soil enzymatic and microbial activities were stimulated by 0.5 mg·kg-1 exogenous Cd, but inhibited at higher Cd dosages. The phenomena suggested the hormetic response to 0.5 mg·kg-1 Cd was highly generalizable concerning soil enzymes and microbial activity. However, the response disappeared after incubation for >10 days. Soil respiration was also initially enhanced by exogenous Cd and decreased after consumption of labile soil organic matter. The metagenomic results revealed Cd stimulation of genes involved in labile soil organic matter decomposition. Additionally, Cd enriched the antioxidant enzymatic activity and abundances of the corresponding marker genes, rather than genes involved in the efflux-mediated heavy metal resistance. The microbes enhanced their primary metabolism to make up the energy gaps, with hormesis evident. The hormetic response disappeared after the labile compounds in soil were exhausted. Overall, this study illustrates the dose-dependence and temporal variation of stimulants and provides a novel and feasible strategy for the study of Cd in soil microorganisms.

[Contribution of environmental lead exposure to blood lead level among infants based on IEUBK model].

OBJECTIVE: To evaluate the influence of environmental lead exposure on infant's blood lead through integrated exposure uptake biokinetic model for lead in children (IEUBK) model, based on environmental lead and prenatal lead exposure. METHODS: The data is from a prospective study conducted among pregnant women during 2005 -2007. Blood lead of the pregnant women in the late pregnancy, environmental lead values including lead concentration in soil, air and drink-water were measured. Moreover, the blood lead concentrations of infants were measured as well. RESULTS: Infants were exposed to lead from the pregnant women during the pregnancy, and in the late pregnancy the geometric mean blood lead of pregnant women was (40.3 +/- 3.7) microg/L. The geometric mean blood lead concentration of six-month old infants was (54.7 +/- 6.7) microg/L and there were 17.3% infants whose blood lead concentration were above 100 microg/L. Lead in soil,atmosphere and drink-water were 45.57 mg/kg, 0.023 microg/m3 and 3.25 microg/L respectively. While based on the calculation of the IEUBK model, the value attributed to environmental lead exposure was 12.4 microg/L, accounting for 22.7% of the real blood lead level. CONCLUSION: The results indicated that environmental lead contamination in the rural area might not be the main reason of elevation in blood lead among infants, other lead resources such as food lead exposure might be the major sources for the intake of lead among infants and should be paid more attentions in future.

[Effects of oxidative stress and NF-kappaB levels in peripheral blood mononuclear cells on development of silicosis].

OBJECTIVE: To investigate the change of indicators of oxidative stress in serum and NF-kappaB in peripheral blood mononuclear cells of patients with silicosis, and explore the mechanism of the development of silicosis. METHODS: The subjects were divided into (1) 200 workers exposed to SiO2 for at least 1 years in a foundry served as the dust-exposure group; (2) 130 cases with silicosis (I phase silicosis 64 cases, II phase 46 cases III phase 20 cases) served as the silicosis group; (3) 32 cases with 0+ phase silicosis in the foundry served as the observed group,(4)100 subjects from a hotel served as the control group. The serum including superoxide dismutase (SOD), nitric oxide (NO), serum glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), nitric oxide synthase (NOS), lipid malondialdehyde (MDA) and NF-kappaB protein levels in peripheral blood mononuclear cells were determined, respectively. RESULTS: Compared with the control group, NO levels in dust-exposed group and silicosis group significantly increased, and SOD decreased significantly (P < 0.05 or P < 0.01). Compared with the control group and dust-exposed group, T-AOC, NOS, MDA levels in silicosis group significantly increased (P < 0.05 or P < 0.01). GSH-Px in dust-exposed group and silicosis group were (231.164 +/- 36.484) and (270.469 +/- 39.228)U/ml, respectively which were significantly than that [(223.360 +/- 46.838) U/ml] in control group (P < 0.05 or P < 0.01), and there was significant difference of GSHPx between the silicosis group and the dust-exposed group significantly (P < 0.01) . GSH-Px level [(290.750 +/- 39.129) U/ml] in III phase silicosis group were significantly higher than those [(256.906 +/- 21.41) and (259.594 +/- 34.79) U/ml] in observation group and I phase silicosis group (P < 0.05). NF-kappaB levels [(72.06 +/- 9.12) and (85.25 +/- 11.64) ng/L] in dust-exposed group and silicosis group were significantly higher than that [(59.71 +/- 9.27) ng/L] in control group (P < 0.01), and there was significant difference of between the silicosis group and the dust-exposed group (P < 0.01). There was a positive correlation between serum GSH-Px level and the silicosis stages (r = 0.507, P < 0.01). Also there was a positive correlation between NF-kappaB level and silicosis stages, age, GSH-Px or NO levels (r = 0.376, 0.243, 0.233, 0.221, P < 0.01). CONCLUSION: The imbalance of oxidative and anti-oxidation system and the activation of NF-kappaB are related with the occurrence and development of silicosis. The monitoring of oxidative stress indicators and NF-kappaB is beneficial to the prediction and prognosis assessment of silicosis.