With a pace of about twice the observed rate of global warming, the temperature on the Qinghai-Tibetan Plateau (Earth's 'third pole') has increased by 0.2°C per decade over the past 50 years, which results in significant permafrost thawing and glacier retreat. Our review suggested that warming enhanced net primary production and soil respiration, decreased methane (CH 4 ) emissions from wetlands and increased CH 4 consumption of meadows, but might increase CH 4 emissions from lakes. Warming-induced permafrost thawing and glaciers melting would also result in substantial emission of old carbon dioxide (CO 2 ) and CH 4 . Nitrous oxide (N 2 O) emission was not stimulated by warming itself, but might be slightly enhanced by wetting. However, there are many uncertainties in such biogeochemical cycles under climate change. Human activities (e.g. grazing, land cover changes) further modified the biogeochemical cycles and amplified such uncertainties on the plateau. If the projected warming and wetting continues, the future biogeochemical cycles will be more complicated. So facing research in this field is an ongoing challenge of integrating field observations with process-based ecosystem models to predict the impacts of future climate change and human activities at various temporal and spatial scales. To reduce the uncertainties and to improve the precision of the predictions of the impacts of climate change and human activities on biogeochemical cycles, efforts should focus on conducting more field observation studies, integrating data within improved models, and developing new knowledge about coupling among carbon, nitrogen, and phosphorus biogeochemical cycles as well as about the role of microbes in these cycles.

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[1] The study aimed to understand the methane (CH 4 ) emission and its controlling factors in the Three Gorges Reservoir Region and to explore its implication for large dams. We measured CH 4 emissions from four vegetation stands in newly created marshes in the drawdown area of the Three Gorges Reservoir, China, in the summer of 2008. The results showed highly spatial variations of methane emissions among the four stands, with the smallest emission (0.25 ± 0.65 mg CH 4 m À2 h À1) in the Juncus amuricus stand, and the greatest (14.9 ± 10.9 mg CH 4 m À2 h À1) in the Scirpus triqueter stand. We found that the spatial variations of CH 4 emissions are caused by difference in standing water depth and dissolved organic carbon (DOC). Results also showed a special seasonal variation of CH 4 emissions in this area, i.e., maximal emissions in early July followed by a low and steady value before the winter flooding. The seasonality of CH 4 emissions was found closely related to temperature and standing water depth. Because of the large area of the drawdown zones for global dam reservoirs and a large CH 4 emission rate, such newly created marshes should not be neglected when estimating CH 4 emissions from reservoirs.

Gao et al.: Impacts of grazing intensity on nitrogen pools and nitrogen cycle in an alpine meadow on the eastern Tibetan Plateau - Abstract. Grazers may influence nitrogen (N) pools and alter N inputs and outputs (losses) to the ecosystem in a number of ways. In this study, we evaluated N pools within the plant-soil system (0-30 cm) and soil N transformation under three different grazing intensities by yaks (light: 1.2, moderate: 2.0, and heavy: 2.9 yaks ha -1 ) in an alpine meadow on the eastern Tibetan Plateau. Total plant and soil N at 0-30 cm depth tended to increase as grazing intensity increasing (plant N: 26.6, 31.4 and 36.7 g m -2 ; soil N: 905, 939 and 1125 g m -2 for light, moderate and heavy grazing, respectively). Soil N transformation rates, such as net N mineralization, gross nitrification, denitrification and N 2 O emissions, generally increased under heavy grazing intensity. Results indicate that heavy grazing intensity accelerated the N cycling rates between system components and leaded to increases in plant-soil system N in this alpine meadow.