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Based on the remote sensing and meteorological data collected from the 1981-2004 period, we calculated the alpine grassland Net Primary Productivity (NPP) in Northern Tibet using the Carnegie-Ames-Stanford Approach (CASA), and subsequently analyzed the trend of grassland NPP changes and its response to climate change from 1981 to 2004. The results show that alpine grassland NPP in Northern Tibet was very low in the last 24 years with a relatively large yearly variation. Most of the grassland area (88.61%) in Northern Tibet did not show a significant annual NPP change. The area with a significant decrease of annual NPP variation accounted for only 11.30% of the total grasslands surface, whereas that with a significant increase accounted for 0.09%. In recent years, the precipitation variation in Northern Tibet resulted in an increase of grassland NPP, though solar radiation resulted in decreased grassland NPP. During the 1981-2004 period, total solar radiation, precipitation and temperature, with a decreasing impact magnitude factor, have impacted the grassland NPP in Northern Tibet. The impact of regional climate change on grassland NPP was overall more detrimental than positive.

Epidemiological studies link ambient fine particulate matter (PM2.5) pollution to abnormalities in the male reproductive system. However, few toxicological studies have investigated this potentially important adverse effect of PM2.5 pollution. Therefore, in the present study, we analyzed the effects of PM2.5 exposure on spermatogenesis and hypothalamic-pituitary-gonadal (HPG) axis in a murine model. Fourteen male C57BL/6J mice were subjected to a 4-month exposure to filtered air or concentrated ambient PM2.5 (CAP). Their sperm count, testicular histology, spermatogenic parameters, and the major components of HPG axis were assessed. Exposure to CAP significantly reduced sperm count in the epididymis. This was accompanied by Sertoli cell vacuolization, immature germ cell dislocation, and decreases in pachytene spermatocytes and round spermatids of stage VII seminiferous tubules, suggesting a marked impairment of spermatogenesis in these mice. This impairment of spermatogenesis appeared to be attributable to a suppression of HPG axis subsequent to CAP exposure-induced hypothalamic inflammation, as exposure to CAP significantly increased TNFα and IL1b mRNA levels and meanwhile decreased gonadotropin-releasing hormone mRNA expression in the hypothalamus. Moreover, CAP exposure significantly reduced circulating testosterone and follicle-stimulating hormone, testicular testosterone and mRNA expression of follicle-stimulating hormone target gene SHBG and luteinizing hormone target genes P450scc, 17βHSD, and StAR. The present data demonstrate that exposure to ambient PM2.5 impairs spermatogenesis in murine model, raising the concern over effects of ambient PM2.5 pollution on the male reproductive function.

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Detection and identification of the impacts of climate change on ecosystems have been core issues in climate change research in recent years. In this study, we compared average annual values of the normalized difference vegetation index (NDVI) with theoretical net primary productivity (NPP) values based on temperature and precipitation to determine the effect of historic climate change on global grassland productivity from 1982 to 2011. Comparison of trends in actual productivity (NDVI) with climate-induced potential productivity showed that the trends in average productivity in nearly 40% of global grassland areas have been significantly affected by climate change. The contribution of climate change to variability in grassland productivity was 15.2–71.2% during 1982–2011. Climate change contributed significantly to long-term trends in grassland productivity mainly in North America, central Eurasia, central Africa, and Oceania; these regions will be more sensitive to future climate change impacts. The impacts of climate change on variability in grassland productivity were greater in the Western Hemisphere than the Eastern Hemisphere. Confirmation of the observed trends requires long-term controlled experiments and multi-model ensembles to reduce uncertainties and explain mechanisms.

Global change caused by increasing greenhouse gas (GHG) emission has become a common concern of the international community. As the largest emitter of GHGs and the second largest irrigator in the world, a clear understanding of how much GHG is emitted from irrigation in China is of great importance. But no previous studies address this question. So based on Chinese official statistical data, this study estimates GHG emissions from agricultural irrigation in order to inform strategies for reasonable use of water resources and emission reduction. The study finds that in 2010 the total carbon dioxide (CO 2 ) equivalent (CO 2 -e) emission from agricultural irrigation is 36.72~54.16 Mt. Emissions from energy activities in irrigation (including water pumping and conveyance) account for 50 %~70 % of total emissions from energy activities in the agriculture sector. Ground water pumping is the biggest emission source, accounting for 60.97 % of total irrigation emissions. Given the extent of global ground water over exploitation, balancing conservation and exploitation of ground water resources is very important to both emission reduction and sustainable development. The GHG emission intensity of irrigation depends largely on water use efficiency, so improvement of water use efficiency (both technical and managerial) can be an effective way to reduce emissions. Enhanced overall management of water utilization, balanced exploitation of water resources to avoid excessive ground water consumption, and active promotion of water use efficiency can contribute to reducing GHG emissions and pressure on water resources and advance sustainable agricultural production.

Assessment of indirect emission factors (EF 5r ) of nitrous oxide (N 2 O) from agricultural river networks remains challenging, and results are uncertain due to limited data availability. This study compared two methods of assessing EF 5r using data from long-term observations at high temporal resolution in a typical agricultural catchment in subtropical central China. The concentration method (method 1) and the Intergovernmental Panel on Climate Change (IPCC) 2006 method (method 2) were employed to evaluate the emission factor. EF 5r estimated using method 1 (i.e., EF 5r1 ) was 0.00077 ± 0.00025 (0.00038−0.00097). EF 5r calculated using method 2 (i.e., EF 5r2 ) was lower than EF 5r1 , with a mean value of 0.00004 (0.000015−0.00012). Both EF 5r1 and EF 5r2 were significantly lower than the IPCC 2006 default value of 0.0025, suggesting that N 2 O emissions from China and world river networks may be grossly overestimated. A complex N 2 O production pathway and diffusion mechanism were responsible for the transfer of N 2 O from the sediment to river water and then to the atmosphere. These findings provide essential data for refining national greenhouse gas inventories and contribute evidence for downward revision of indirect emission factors adopted by the IPCC.