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Hao Y.B.,University of Chinese Academy of Sciences | Cui X.Y.,University of Chinese Academy of Sciences | Wang Y.F.,University of Chinese Academy of Sciences | Mei X.R.,Institute of Environment and Sustainable Development in Agriculture CAAS | And 4 more authors.
Wetlands | Year: 2011

Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured at Zoige wetland using the eddy covariance technique. Analysis of CO2 fluxes in two years showed Zoige wetland was a net CO2 sink of -47.1 and -79.7 gC m-2 a-1 in 2008 and 2009, respectively. The peak NEE value was -0.54 mg CO2 m-2 s-1 (the negative value signifies net ecosystem carbon gain from air). The maximal daily integrated NEE was -4.1 gC m-2 d-1 during the peak growth season (from July to August). Gross ecosystem photosynthesis was likely more variable than ecosystem respiration at both seasonal and interannual timescales in this wetland. Our data strongly suggested that the combination of precipitation and temperature, as well as phenological stage of vegetation, controlled the dynamics of ecosystem carbon gain, even in drought years. Therefore, an accurate representation of these parameters in climate models is critical to the success of forecasting carbon budgets of alpine wetlands. © Society of Wetland Scientists 2011.


Zhang Q.,Institute of Environment and Sustainable Development in Agriculture CAAS | Wang Y.,Institute of Environment and Sustainable Development in Agriculture CAAS | Wu Y.,Institute of Environment and Sustainable Development in Agriculture CAAS | Wang X.,Chinese Research Academy of Environmental Sciences | And 3 more authors.
Soil Science Society of America Journal | Year: 2013

Little information is available regarding the effects of biochar amendment on soil thermal properties and soil temperature, especially under field conditions. The possible changes in soil thermal conductivity, surface reflectance, and temperature resulting from biochar addition might affect other biophysical-chemical processes in the soil. We examined the effects of biochar amendment on the thermal conductivity, surface reflectance, and temperature of soil. Soil thermal conductivity, reflectance, and temperature at a 5-cm depth were measured and monitored in an experimental field using a portable soil thermal property analyzer, a portable full-range spectrometer, and temperature and water potential probes. The field was located in the North China Plain and had been cropped in a winter wheat (Triticum aestivum L)-maize (Zea mays L.) system for 5 yr. With biochar amendment, soil thermal conductivity was decreased significantly by 3.48 and 7.49% with 4.5 (B4.5) and 9.0 t ha-1 yr-1 (B9.0) of biochar addition, respectively, which was consistent with a decrease in soil bulk density. Soil water potential slightly increased under B4.5 treatment but decreased under B9.0 treatment relative to the control. Reflectance increased in the near-ultraviolet and blue-light wavelengths (350-513 nm) and decreased in the infrared wavelength range (520-2350 nm) with biochar amendment. Biochar amendment reduced diurnal soil-temperature fluctuations on both daily and seasonal scales, although the annual average daily soil temperatures at a 5-cm depth showed no significant difference among treatments. Comparison with the control showed that biochar treatment moderated soil temperature extremes, lowering the temperature when soil temperature was high and raising it when soil temperature was low. This moderating capability was mostly within ±0.4 and ±0.8°C for mean daily temperature and mean diurnal temperature of soil, respectively. The effect of biochar amendment on soil temperatures can be explained by the combined action of changes in soil thermal conductivity and reflectance. © Soil Science Society of America, All rights reserved.


Hao Y.,University of Chinese Academy of Sciences | Wang Y.,University of Chinese Academy of Sciences | Mei X.,Institute of Environment and Sustainable Development in Agriculture CAAS | Cui X.,University of Chinese Academy of Sciences
Plant Ecology | Year: 2010

In water-limited grassland ecosystems, discrete and occasional precipitation events trigger brief but important episodes of biological activity. Differential responses of above- and below-ground biota to precipitation pulses may constrain biogeochemical transformations at the ecosystem scale. We examined the short-term dynamics of the whole ecosystem response to small precipitation events during 2003 and 2004 in a steppe on the Inner Mongolia Plateau. The results indicate that changes in soil moisture occur, with a 1-2 day time lag, only when the amount of precipitation exceeds 3 mm (from day of year [DOY] 120 to DOY 180) or 5 mm (after DOY 180). The interception of the developing plant canopy is a primary reason for the different temporal precipitation threshold. The lower threshold of effective rain is different between (Re,3 mm) and Gross Ecosystem Production (GEP,5 mm). The NEE reached a maximum 4-5 days after the end of effective rain events and dropped to 60-70% of the original fluxes after 10 days. However, the drop in GEP was greater than that of NEE and reached 30-50% of the original fluxes after 10-15 days without "effective rainfall." The characteristics of the response time can be attributed to the variation in soil water content and the time of readjusting for the ecological processes after the effective rainfall. In addition, the independent responses of photosynthesis, respiration and evapotranspiration to precipitation probably contributed to this time lag. The results support the hypothesis that the concept of an ecologically significant rainfall event can be developed for an ecosystem. © 2010 Springer Science+Business Media B.V.


Wang Y.F.,University of Chinese Academy of Sciences | Cui X.Y.,University of Chinese Academy of Sciences | Hao Y.B.,University of Chinese Academy of Sciences | Mei X.R.,Institute of Environment and Sustainable Development in Agriculture CAAS | And 4 more authors.
Science of the Total Environment | Year: 2011

The CO2 flux was measured by the eddy covariance method on a temperate Leymus chinensis steppe over a period of 17months spanning two consecutive growing seasons. The amount of precipitation was nearly normal, but it was low in the early and high in the late growing period in 2006. In the 2007 growing season, the amount of precipitation was about 45% less than the multi-year average and more evenly distributed. Comparisons were made between a moderately grazed site and a 28-year-old fenced site. The maximum instantaneous CO2 release and uptake rates were 0.12 (May) and -0.11mg CO2m-2s-1 (July) at the fenced site, and 0.11 and -0.16mg CO2m-2s-1 (both in July) at the grazed site. In both growing seasons, the grazed site always had a higher daily uptake rate or lower release rate than the fenced site. The grazed site was a CO2 sink during the growing season of 2007 and a CO2 source in the growing season of 2006, whereas the fenced site was a CO2 source in both seasons. Lower precipitation decreased CO2 loss during the growing season more in the grazed site than in the fenced site, mainly because of depression of total ecosystem respiration (Re) in the former and stimulation in the latter. During the dormant season (from October to April), the fenced and grazed sites released 60.0 and 32.4g of C per m2, respectively. Path analysis showed that temperature had the greatest effect on daily variation of ecosystem CO2 exchange during the growing seasons at the two study sites. The results suggest that decrease of precipitation and/or increase of temperature will likely promote C loss from L. chinensis steppes, whether fenced or grazed, and that a grazed site is more sensitive. © 2011 Elsevier B.V.

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