Search

Abstract: Four sets of remote sensing images from 1987, 1994, 2000, and 2006, 50 years of meteorological and soil moisture data corresponding to different desertified lands were combined with populations and livestock data to analyze the process and cause of desertification in a portion of the Qinghai–Tibetan Plateau (QTP). It showed that surface soil temperature in the region has increased at an average rate of 0.6 °C per decade between 1980 and 2005, the thawing days on the surface have increased by 60 days from 1983 to 2001, and the depth of the seasonal thawing layer has increased by 54 cm, 102 cm and 77 cm in April, May and June, respectively, from 1983 to 2003. As a result, the upper soil layer has become drier due to the thickening active layer and soil water infiltration. These changes, in turn, have inhibited the growth of alpine meadow vegetation that has shallow root systems. It is concluded that climate warming and permafrost thawing have caused desertification in grazing regions of the Qinghai–Tibetan Plateau (QTP). [Copyright &y& Elsevier]

Partitioning evapotranspiration ( ET ) into soil evaporation ( E a ) and plant transpiration ( T r ) is important to understand response of ecosystem water balance to climate warming. A field experiment was conducted to investigate the effect of additional infrared radiation as a simulation of climate warming (W1: 130 W m −2 and W2: 150 W m −2 ) on ET , E a , T r , and soil moisture in an alpine meadow in the Qinghai-Tibet plateau (QTP). ET was calculated by using an energy balance model and a soil moisture correction function. E a in warm-rainy season was estimated by a multiple linear regression with latent heat, soil moisture in 0–10 cm layer and soil temperature in 20 cm depth as independent variables. T r was quantified as the difference between ET and E a . Results showed that annual ET increased by 92 mm and 89 mm, annual E a increased by 29.12 mm and 33.37 mm, and annual T r increased by 63.53 mm and 55.81 mm in W1 and W2 treatments, respectively. The results suggest that T r stimulation accounts for most of the ET change and is the major reason for the soil surface layer drying in alpine meadow ecosystem on the QTP. [ABSTRACT FROM AUTHOR]

Responses of ecosystem carbon (C) fluxes to human disturbance and climatic warming will affect terrestrial ecosystem C storage and feedback to climate change. We conducted a manipulative experiment to investigate the effects of warming and clipping on soil respiration (Rs), ecosystem respiration (ER), net ecosystem exchange (NEE) and gross ecosystem production (GEP) in an alpine meadow in a permafrost region during two hydrologically contrasting years (2012, with 29.9% higher precipitation than the long-term mean, and 2013, with 18.9% lower precipitation than the long-tem mean). Our results showed that GEP was higher than ER, leading to a net C sink (measured by NEE) over the two growing seasons. Warming significantly stimulated ecosystem C fluxes in 2012 but did not significantly affect these fluxes in 2013. On average, the warming-induced increase in GEP (1.49 µ mol m−2s−1) was higher than in ER (0.80 µ mol m−2s−1), resulting in an increase in NEE (0.70 µ mol m−2s−1). Clipping and its interaction with warming had no significant effects on C fluxes, whereas clipping significantly reduced aboveground biomass (AGB) by 51.5 g m−2 in 2013. These results suggest the response of C fluxes to warming and clipping depends on hydrological variations. In the wet year, the warming treatment caused a reduction in water, but increases in soil temperature and AGB contributed to the positive response of ecosystem C fluxes to warming. In the dry year, the reduction in soil moisture, caused by warming, and the reduction in AGB, caused by clipping, were compensated by higher soil temperatures in warmed plots. Our findings highlight the importance of changes in soil moisture in mediating the responses of ecosystem C fluxes to climate warming in an alpine meadow ecosystem. [ABSTRACT FROM AUTHOR]