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Ganjurjav H.,Chinese Academy of Agricultural Sciences | Ganjurjav H.,Key Laboratory for Agro Environment and Climate Change | Gao Q.,Chinese Academy of Agricultural Sciences | Gao Q.,Key Laboratory for Agro Environment and Climate Change | And 12 more authors.
PLoS ONE | Year: 2015

To analyze CO2 fluxes under conditions of climate change in an alpine meadow on the central Qinghai-Tibetan Plateau, we simulated the effect of warming using open top chambers (OTCs) from 2012 to 2014. The OTCs increased soil temperature by 1.62°C (P < 0.05), but decreased soil moisture (1.38%, P < 0.05) during the experiments. The response of ecosystem CO2 fluxes to warming was variable, and dependent on the year. Under conditions of warming, mean gross ecosystem productivity (GEP) during the growing season increased significantly in 2012 and 2014 (P < 0.05); however, ecosystem respiration (ER) increased substantially only in 2012 (P < 0.05). The net ecosystem CO2 exchange (NEE) increased marginally in 2012 (P = 0.056), did not change in 2013(P > 0.05), and increased significantly in 2014 (P = 0.034) under conditions of warming. The GEP was more sensitive to climate variations than was the ER, resulting in a large increase in net carbon uptake under warming in the alpine meadow. Under warming, the 3-year averages of GEP, ER, and NEE increased by 19.6%, 15.1%, and 21.1%, respectively. The seasonal dynamic patterns of GEP and NEE, but not ER, were significantly impacted by warming. Aboveground biomass, particularly the graminoid biomass increased significantly under conditions of warming. Soil moisture, soil temperature, and aboveground biomass were the main factors that affected the variation of the ecosystem CO2 fluxes. The effect of warming on inter- and intra-annual patterns of ecosystem CO2 fluxes and the mechanism of different sensitivities in GEP and ER to warming, require further researched. Copyright: © 2015 Ganjurjav et al.

Gao Q.,Chinese Academy of Agricultural Sciences | Gao Q.,Key Laboratory for Agro Environment and Climate Change | Wan Y.,Chinese Academy of Agricultural Sciences | Wan Y.,Key Laboratory for Agro Environment and Climate Change | And 10 more authors.
International Journal of Remote Sensing | Year: 2013

Using the Carnegie-Ames-Stanford Approach (CASA) model on remote-sensing (RS), climatic, and other related data from 1981 to 2004, the researchers estimated the net primary productivity (NPP) of alpine grassland in northern Tibet. Geographical information system (GIS) techniques were used to analyse the spatial pattern of change in the NPP of alpine grassland and its response to the intensity of human activity. The researchers found that the mean values of NPP on flat (slope gradients <1°) and sunny slopes were relatively lower. Between 1981 and 2004, the NPP of alpine grassland in northern Tibet tended to decrease, but with relatively large annual fluctuations. In northern Tibet, the alpine grassland NPP for high-elevation regions has a greater proportion of area (over 26%) showing a decreasing trend. The change is more significant in areas where the slope is 15-30° and aspect has little influence on the extent of the change. The negative effects of local residential areas on the rate of change of alpine grassland NPP are smaller than those of roads. © 2013 Copyright Taylor and Francis Group, LLC.

Ganjurjav H.,Chinese Academy of Agricultural Sciences | Ganjurjav H.,Key Laboratory for Agro Environment and Climate Change | Duan M.-J.,Beijing Institute of Landscape Architecture | Wan Y.-F.,Chinese Academy of Agricultural Sciences | And 10 more authors.
Rangeland Journal | Year: 2015

Grazing by large herbivores may have a strong impact on plant diversity and productivity, but the effects are expected to vary with grazing pressure. The changes in productivity and species diversity of Stipa purpurea-dominated semi-arid alpine steppe grassland were measured under four different stocking rates of Tibetan sheep [no grazing, light (2.4 sheep units ha-1), moderate (3.6 sheep units ha-1), and heavy (6.0 sheep units ha-1) grazing] in a 5-year (2006-2010) grazing experiment on the Qinghai-Tibetan Plateau, China. Herbage mass and aboveground net primary productivity of alpine steppe declined significantly with increasing stocking rate (P<0.05). Over the 5 years of the experiment, the proportion of forbs and sedges increased significantly under light and moderate grazing; the proportion of grasses decreased significantly, whereas the proportion of S. purpurea did not change compared with the no grazing treatment. Species diversity was highest under moderate grazing and was significantly higher than the no grazing treatment in 2 years (2008 and 2010). Moderate grazing enhanced the species diversity of the plant community due to an increase in the proportion of forbs. There were significant positive linear correlations between herbage mass and species diversity under no and light grazing. Species diversity was not related to productivity under moderate and heavy grazing. In conclusion, grazing by sheep reduced plant productivity; plant diversity increased under low and moderate grazing, and was as a result of changes in the composition of the plant community of a semi-arid alpine steppe. © 2015 Australian Rangeland Society.

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