Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.
Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were ?7.4 and 5.4 g·m?2·d?1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were ?12.8 and 5.8 g·m?2·d?1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m?2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m?2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m?2·s?1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature. 相似文献
Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions. As a part of ChinaFLUX, eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia, China during 2003–2004 to quantify the response of carbon exchange to environmental changes. Results showed that gross ecosystem production (FGEP) and ecosystem respiration (Reco) of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season. Temperature was the dominant factor affecting FGEP and Reco in 2003, whereas soil moisture imposed a significant influence on both Reco and FGEP in 2004. Under wet conditions, Reco showed an exponentially increasing trend with temperature (Q10 = 2.0), but an apparent reduction in the value of Reco and its temperature sensitivity were observed during the periods of water stress (Q10=1.6). Both heat and water stress can cause decrease in FGEP. The seasonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation. With less precipitation in 2003, the steppe sequestrated carbon in June and July, and went into a senescence in early August due to water stress. As compared to 2003, the severe drought during the spring of 2004 delayed the growth of the steppe until late June, and the steppe became a CO2 sink from early July until mid-September, with ample precipitation in August. The semi-arid steppe released a total of 9.7 g C·m?2 from May 16 to the end of September 2003, whereas the net carbon budget during the same period in 2004 was close to zero. Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands. 相似文献
On the basis of the one-dimension infinite element theory, the coordinate translation and shape function of 3D point-radiate 8-node and 4-node infinite elements are derived. They are coupled with 20-node and 8-node finite elements to compute the compression distortion of the prestressed an- chorage segment. The results indicate that when the prestressed force acts on the anchorage head and segment, the stresses and the displacements in the rock around the anchorage head and segment con- centrate on the zone center with the anchor axis, and they decrease with exponential forms. Therefore, the stresses and the displacement spindles are formed. The calculating results of the infinite element are close to the theoretical results. This indicates the method is right. This article introduces a new way to study the mechanism of prestressed anchors. The obtained results have an important role in the re- search of the anchor mechanism and engineering application. 相似文献
Journal of Oceanology and Limnology - To assist the researches of toxic and harmful algae and provide government workers with judgment basis for decision-making related events, we established a... 相似文献