Sewage sludge application stimulated soil N2O emissions with a low heavy metal pollution risk in Eucalyptus plantations.

Sewage sludge (SS) has been extensively used as an alternative fertilizer in forest plantations, which are beneficial in supplying timbers and mitigating climate change. However, whether the extra nitrogen (N) applied by SS would enhance the soil nitrous oxide (N2O) emission, an important greenhouse gas, in forest plantations have not been well understood. The objective of this study is to evaluate the ecological effects of SS application on soils, by investigating the soil N2O emission and the toxicity of the potentially toxic elements (PTEs) in soil. A field fertilization experiment was conducted in Eucalyptus plantations with four fertilization rates (0 kg m-2, 1.5 kg m-2, 3.0 kg m-2, and 4.5 kg m-2). The soil N2O emissions were monitored at a soil depth of 0-10 cm using static chamber method, soil chemical properties, and PTEs were determined at soil depths of 0-10 cm, 10-20 cm, and 20-40 cm. The average soil N2O emission rate was 8.1 µg N2O-N h-1 m-2 in plots without SS application (control). The application of SS significantly increased the soil N2O emissions by 7-10 times as to control. The increased N2O emissions were positively related to the soil total phosphorus and nitrogen and negatively correlated with copper and zinc, which increased with the SS application. However, the potential ecological risk index (Ei) and the comprehensive potential ecological risk index (RI) of PTEs were lower than 40 and 150 respectively, which indicating a low toxicity of PTEs to soil health. After seven months of SS application, the priming effects of SS on soil N2O emissions gradually diminished. These findings suggest that the application of SS may increase N2O emissions at the initial stages of application (<7 months) and may have a low PTEs pollution risk, even at a high SS addition rate (4.5 kg m-2).

[Significance and mechanisms of overexpression of PAK1 gene in epithelial ovarian neoplasms].

OBJECTIVE: To investigate the significance and mechanisms of overexpression of p21-activated kinase 1 gene (PAK1) in epithelial ovarian neoplasms. METHODS: Immunohistochemistry, fluorescence in situ hybridization and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling methods were used to examine the protein expression and amplification of PAK1 and cell apoptosis in 30 benign ovarian adenomas, 20 borderline tumors and 80 ovarian carcinomas by tissue microarray. RESULTS: In immunohistochemistry study, overexpression of PAK1 protein was observed in 7 (25.9%) informative benign ovarian adenomas, 7 (36.8%) borderline tumors and 53 (68.8%) ovarian carcinomas. A significant inverse correlation of PAK1 overexpression and cell apoptosis was observed in these epithelial ovarian neoplasm cohorts (P = 0.002). In addition, 27/31 (87.1%) poorly differentiated (G3) carcinomas showed overexpression of PAK1, the frequency was significantly higher than that in tumors of G1 - G2 (26/46, 56.5% , P =0.01). In fluorescence in situ hybridization study, only 2 (4.7%) informative ovarian carcinomas showed amplification of PAK1 gene. None of the borderline and benign ovarian tumors showed PAK1 amplification. CONCLUSION: Overexpression of PAK1 protein may be involved in the tumorigenesis of epithelial ovarian neoplasms and it is associated closely with the malignant histological phenotype of ovarian carcinomas. Mechanism other than gene amplification of PAK1 may play a more important role in the regulation of protein expression of PAK1 in ovarian tumors.