A detailed analysis of the photoluminescence ͑PL͒ from Si nanocrystals ͑NCs͒ embedded in a silicon-rich SiO 2 matrix is reported. The PL spectra consist of three Gaussian bands ͑peaks A , B, and C͒, originated from the quantum confinement effect of Si NCs, the interface state effect between a Si NC and a SiO 2 matrix, and the localized state transitions of amorphous Si clusters, respectively. The size and the surface chemistry of Si NCs are two major factors affecting the transition of the dominant PL origin from the quantum confinement effect to the interface state recombination. The larger the size of Si NCs and the higher the interface state density ͑in particular, Siv O bonds͒, the more beneficial for the interface state recombination process to surpass the quantum confinement process, in good agreement with Qin's prediction in Qin and Li ͓Phys. Rev. B 68, 85309 ͑2003͔͒. The realistic model of Si NCs embedded in a SiO 2 matrix provides a firm theoretical support to explain the transition trend.

Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550 °C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8 t ha with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8 t ha (B8) and 16 t ha (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8 t ha straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2 mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2 mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16 treatment. In conclusion, application of carbonized crop residue as biochar, especially at a rate of 16 t ha, could be a potential solution to recover the depleted SOC and enhance the formation of macro-aggregates in Loess Plateau soils of China.

In order to clarify the ensiling characteristics of stylo (Stylosanthes guianensis Swartz), the effects of wilting (no wilting, light wilting and heavy wilting) and storage temperatures (10°C, 20°C, 30°C and 40°C) on the fermentation quality and aerobic stability of stylo silage were investigated. Wilting had no significant influence on the contents of crude protein, ether extract and acid detergent fiber, and numbers of lactic acid bacteria, aerobic bacteria, yeasts and mold (P > 0.05). Heavy wilted material, wilted for 12 h, had higher neutral detergent fiber content and lower water-soluble carbohydrate content than unwilted and light wilted materials (P < 0.05). Wilting and storage temperatures had significant effects on pH value, acetic acid, butyric acid and NH(3) -N contents of stylo silage (P < 0.01 or P < 0.05). Wilting tended to reduce acetic acid and NH(3) -N contents and improve the fermentation quality of stylo silage. In all the silages, no wilting silage ensiled at 30°C had the highest butyric acid content (P < 0.05). High temperature of 40°C markedly restricted the growth of lactic acid bacteria and aerobic bacteria in silage, irrespective of wilting. The wilted silage or silage stored at low temperature had poor aerobic stability.

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As part of its Paris Agreement commitment, China pledged to peak carbon dioxide (CO 2) emissions around 2030, striving to peak earlier, and to increase the non-fossil share of primary energy to 20% by 2030. Yet by the end of 2017, China emitted 28% of the world's energy-related CO 2 emissions, 76% of which were from coal use. How China can reinvent its energy economy cost-effectively while still achieving its commitments was the focus of a three-year joint research project completed in September 2016. Overall, this analysis found that if China follows a pathway in which it aggressively adopts all cost-effective energy efficiency and CO 2 emission reduction technologies while also aggressively moving away from fossil fuels to renewable and other non-fossil resources, it is possible to not only meet its Paris Agreement Nationally Determined Contribution (NDC) commitments, but also to reduce its 2050 CO 2 emissions to a level that is 42% below the country's 2010 CO 2 emissions. While numerous barriers exist that will need to be addressed through effective policies and programs in order to realize these potential energy use and emissions reductions, there are also significant local environmental (e.g., air quality), national and global environmental (e.g., mitigation of climate change), human health, and other unquantified benefits that will be realized if this pathway is pursued in China.

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Abstract:In the Heihe River basin, China, increased salinity and water shortages present serious threats to the sustainability of arid wetlands. It is critical to understand the interactions between soil water and salts (from saline shallow groundwater and the river) and their effects on plant growth under the influence of shallow groundwater and irrigation. In this study, the Hydrus-1D model was used in an arid wetland of the Middle Heihe River to investigate the effects of the dynamics of soil water, soil salinization, and depth to water table (DWT) as well as groundwater salinity on Chinese tamarisk root water uptake. The modeled soil water and electrical conductivity of soil solution (ECsw) are for ECsw, during the model calibration and validation periods, respectively). The calibrated model was used in scenario analyses considering different DWTs, salinity levels and the introduction of preseason irrigation. The results showed that (I) Chinese tamarisk root distribution was greatly affected by soil water and salt distribution in the soil profile, with about 73.8% of the roots being distributed in the 20-60 cm layer; (II) root water uptake accounted for 91.0% of the potential maximal value when water stress was considered, and for 41.6% when both water and salt stress were considered; (III) root water uptake was very sensitive to fluctuations of the water table, and was greatly reduced when the DWT was either dropped or raised 60% of the 2012 reference depth; (IV) arid wetland vegetation exhibited a high level of groundwater dependence even though shallow groundwater resulted in increased soil salinization and (V) preseason irrigation could effectively increase root water uptake by leaching salts from the root zone. We concluded that a suitable water table and groundwater salinity coupled with proper irrigation are key factors to sustainable development of arid wetlands.