Impact of experimental warming on soil temperature and moisture of the shallow active layer of wet meadows on the Qinghai-Tibet Plateau

Climate change is now increasingly evident on the Qinghai-Tibet Plateau and has a strong impact on both the abiotic and biotic components of ecosystems, particularly on permafrost, active layer thickness, vegetation, and soil properties. Permafrost ecosystems are recognized to be sensitive to the influences of the changing climate, which may disturb the permafrost soil carbon (C) pool and lead to huge C emissions. To facilitate the assessment of warming effects on the temperature and moisture patterns in the shallow soil of the active layer of the wet meadows on the Qinghai-Tibet Plateau, near-surface air temperature was passively increased by using open-top chambers (OTCs) with two different temperature increments. Soil temperature and moisture were continuously monitored at depths of 5, 20, and 40 cm at hourly intervals in a wet meadow in the Beiluhe region on the Qinghai-Tibet Plateau from October 1, 2007 to June 24, 2009. When near-surface air temperature increased by 5.29 °C and 1.84 °C in the OTC2 and OTC1 plots, respectively, relative to the control plots, soil temperatures at depths of 5, 20, and 40 cm were seen to increase by 3.84°C, 2.23°C, and 1.42 °C, respectively, in the OTC2 plots and by 0.94°C, 0.27°C, and 0.25 °C, respectively, in the OTC1 plots. Soil moisture content at depths of 5, 20, and 40 cm declined by 8.04%, 1.79%, and 1.52%, respectively, in the OTC2 plots and by 5.33%, 0.69%, and 0.09%, respectively, in the OTC1 plots. Near-surface warming was found to extend the continuous thawing time of the shallow soil, delay the occurrence of the autumnal freezing process, and shorten the duration of continuous freezing. It was also seen to increase both the temperature of the shallow soil and the accumulated temperatures at different depths. Near-surface warming could be one of the main factors leading to the degradation of vegetation, thus threatening the stability of the soil C pool and the ecological safety of the Qinghai-Tibet Plateau.