Knowledge about the role of litter and dung decomposition in nutrient cycling and response to climate change and grazing in alpine ecosystems is still rudimentary. We conducted two separate studies to assess the relative role of warming and grazing on litter mass loss and on the temperature sensitivity of litter and dung mass loss. Experiments were conducted for 1-2 years under a controlled warming-grazing system and along an elevation gradient from 3200 to 3800 m. A free-air temperature enhancement system (FATE) using infrared heaters and grazing significantly increased soil temperatures (average 0.5-1.6 1C) from 0 to 40 cm depth, but neither warming nor grazing affected soil moisture except early in the growing seasons at 30 cm soil depth. Heaters caused greater soil warming at night-time compared with daytime, but grazing resulted in greater soil warming during daytime compared with night-time. Annual average values of the soil temperature at 5 cm were 3.2, 2.4 and 0.3 1C at 3200, 3600 and 3800 m, respectively. Neither warming nor grazing caused changes of litter quality for the first year of the controlled warming-grazing experiment. The effects of warming and grazing on litter mass losses were additive, increasing litter mass losses by about 19.3% and 8.3%, respectively, for the 2-year decomposition periods. The temperature sensitivity of litter mass losses was approximately 11% 1C À1 based on the controlled warming-grazing experiment. The annual cumulative litter mass loss was approximately 2.5 times that of dung along the elevation gradient. However, the temperature sensitivity (about 18% 1C À1 ) of the dung mass loss was about three times that of the litter mass loss. These results suggest greater warming at night-time compared with daytime may accelerate litter mass loss, and grazing will enhance carbon loss to atmosphere in the region through a decrease of litter biomass and an increase of dung production with an increase of stocking rate in future warmer conditions.

Recently, plant-derived methane (CH 4 ) emission has been questioned because limited evidence of the chemical mechanism has been identified to account for the process. We conducted an experiment with four treatments (i.e. winter-grazed, natural alpine meadow; naturally restored alpine meadow eight years after cultivation; oat pasture and bare soil without roots) during the growing seasons of 2007 and 2008 to examine the question of CH 4 emission by plant communities in the alpine meadow. Each treatment consumed CH 4 in closed, opaque chambers in the field, but two types of alpine meadow vegetation reduced CH 4 consumption compared with bare soil, whereas oat pasture increased consumption. This result could imply that meadow vegetation produces CH 4 . However, measurements of soil temperature and water content showed significant differences between vegetated and bare soil and appeared to explain differences in CH 4 production between treatments. Our study strongly suggests that the apparent CH 4 production by vegetation, when compared with bare soil in some previous studies, might represent differences in soil temperature and water-filled pore space and not the true vegetation sources of CH 4 .

Knowledge of the response of litter mass loss to climate warming and litter quality in alpine ecosystems is still sparse. Here, we conducted a 507-day litter decomposition experiment along an elevation gradient from 3200 to 3800 m using different litter types to determine the influences of litter quality and climate change on the elemental mass losses and on the temperature sensitivity of litter mass losses (annual percentage decomposition (%) per 1°C temperature difference). Mass losses of C, nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca), and Magnesium (Mg) decreased with an increase in elevation. In general, N and Na concentrations in litter and ratios of C:N and lignin:N were the best predictors of C mass losses. A higher N concentration and C:N ratio in litter caused greater C mass losses, but higher lignin:N ratio in litter resulted in lower C mass losses. Litter decomposition occurred in a two-stage process. Carbon mass loss in litter was mainly limited by soil temperature in the first growing season of the decomposition period, whereas N concentration and ratios of C:P and N:P limited carbon mass loss in the remaining litter during the second growing season of the decomposition period. Soil moisture appeared not to affect litter mass loss and the temperature sensitivity of litter mass loss of grass litter was greater than that of shrub litter in the alpine region.

The temperature sensitivity of nutrient release from dung decomposition will influence ecosystem nutrient recycling in the future global warming. However, the relationship between temperature and nutrient release is not well understood. We conducted a 2-year-long study to understand the yak dung decomposition and its potential response to climate change along an elevation gradient from 3,200 to 4,200 m above sea level on an alpine meadow on the Qinghai-Tibetan plateau. Mass loss of different chemical components of dung [organic carbon (C), cellulose, hemicellulose, lignin, N, P, potassium (K), calcium (Ca) and magnesium (Mg)] significantly decreased with elevation. The ratios of C:N and N:P in the remaining dung increased significantly with decrease in elevation. The average temperature sensitivities (%°C -1 ) (i.e., increase of the mass loss (%) per 1°C temperature increase among elevations) were approximately 37, 75, 168, 41, 29, 37, 29, 34, and 31% per 1°C warming within a 273-day decomposition period, which decreased with decomposition time, for organic C, cellulose, hemicellulose, lignin, N, P, K, Ca, and Mg, respectively. The temperature sensitivity of organic C mass loss is positively correlated to the C:N ratios in dung. The average temperature sensitivity of phosphorus mass loss was higher than that of nitrogen mass loss for the first 273 days and thereafter this situation was reversed.