The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106km2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation...The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106km2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation. An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux of alpine meadow from July to October, 2003. The continuous carbon flux data were used to analyze the relationship between net ecosystem carbon dioxide exchange (NEE) and photosynthetically active radiation (PAR), as well as the seasonal patterns of apparent quantum yield (α) and maximum ecosystem assimilation (Pmax). Results showed that the daytime NEE fitted fairly well with the PAR in a rectangular hyperbola function, with α declining in the order of peak growth period (0.0244 μmolCO2 · μmol-1PAR) > early growth period > seed maturing period > withering period (0.0098 μmolCO2 · μmol-1PAR). The Pmax did not change greatly during the first three periods, with an average of 0.433 mgCO2 · m-2 · s-1,i.e. 9.829 μmolCO2 · m-2 · s-1. However, during the withering period, Pmax was only 0.35 mgCO2 · m-2 · s-1, i.e. 7.945 μmolCO2 · m-2 · s-1. Compared with other grassland ecosystems, the α of the Tibetan Plateau alpine meadow ecosystem was much lower.展开更多
The Tibetan Plateau is characterized by lower atmospheric pressure, lower air temperature and high daily and seasonal variation due to high elevation. The photosynthesis of aaplants is significantly influenced by thes...The Tibetan Plateau is characterized by lower atmospheric pressure, lower air temperature and high daily and seasonal variation due to high elevation. The photosynthesis of aaplants is significantly influenced by these alpine environmental factors. Apparent quantum yield (αA) is one of the basic parameters of photosynthesis and mass production. Its accuracy determination is of significance to model photosynthesis of C3 plants and global change on the plateau. In the Lhasa Plateau Ecological Station with 65.4 kPa of atmospheric pressure at an elevation of 3688 m, Li-Cor 6400 portable photosynthesis system was used to measure light response curves of winter wheat in different temperatures and intercellular CO2 concentration (C,). The slope of light response curve in weak light area of PFD from 0 to 150 μmol m-2 s-1 was used to evaluate the value of αA. The dependence of αA on temperature and intercellular concentration was analyzed. In 30℃, the average value of αA was 0.0476±0.0038. It is not quite different from the values in low elevation areas. αA is influenced both by temperature and by the ratio of CO2 and O2 partial pressure ([CO2]/[O2]). The measured values in the previous study were much lower. This might be due to systematic errors from instrument and data processing methods. The values of αA decreased linearly with temperature. It decreased 0.0007 in every 1℃ increase of temperature. The decrease slope is similar to those of C3 plants in the previous researches. While [O2] is constant,αA increases with Ciwith a hyperbolic relationship. In comparison with low elevation areas, the αA on the Tibetan Plateau is more sensitive to increase of CO2.展开更多
研究采用目前先进的光合作用测定系统L i-Cor-6400测定濒危物种西藏巨柏的光合作用,自然环境条件下的西藏巨柏光合日进程表现为单峰型曲线,在12:00时左右达到最高峰,其光合作用不存在“午休现象”。在12:00时,西藏巨柏的气孔限制值和水...研究采用目前先进的光合作用测定系统L i-Cor-6400测定濒危物种西藏巨柏的光合作用,自然环境条件下的西藏巨柏光合日进程表现为单峰型曲线,在12:00时左右达到最高峰,其光合作用不存在“午休现象”。在12:00时,西藏巨柏的气孔限制值和水分饱和亏缺分别达到最大值,此时的水分利用效率较高,在9:00时,西藏巨柏获得一天中最大的表观量子效率,水分利用效率达到最大值。其蒸腾速率在13:00时最大,这个时间并不与光合速率最大值同步,这说明在西藏特殊的气候环境条件下,影响光合速率的因素很多。在光合速率的日进程中,高光合速率值(大于4.00μm o lCO2/(m2.s))持续时间在5h左右,这使得西藏巨柏的光合作用产物得以有效积累,也为西藏巨柏在半干旱环境中的生长创造了有利条件。展开更多
基金This work was jointly supported by the Major State Basic Research Development Program of China(Grant No.2002CB412501)the National Natural Science Foundation of China(Grant Nos.30170153 and 30470280)the Key Innovation Project of Institute of Geographic Sciences and Natural Resources Research,CAS(Grant No.CXIOG-E01-03-03).
文摘The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106km2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation. An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux of alpine meadow from July to October, 2003. The continuous carbon flux data were used to analyze the relationship between net ecosystem carbon dioxide exchange (NEE) and photosynthetically active radiation (PAR), as well as the seasonal patterns of apparent quantum yield (α) and maximum ecosystem assimilation (Pmax). Results showed that the daytime NEE fitted fairly well with the PAR in a rectangular hyperbola function, with α declining in the order of peak growth period (0.0244 μmolCO2 · μmol-1PAR) > early growth period > seed maturing period > withering period (0.0098 μmolCO2 · μmol-1PAR). The Pmax did not change greatly during the first three periods, with an average of 0.433 mgCO2 · m-2 · s-1,i.e. 9.829 μmolCO2 · m-2 · s-1. However, during the withering period, Pmax was only 0.35 mgCO2 · m-2 · s-1, i.e. 7.945 μmolCO2 · m-2 · s-1. Compared with other grassland ecosystems, the α of the Tibetan Plateau alpine meadow ecosystem was much lower.
基金This work was supported by the National Key Basic Research and Development Project(Grant No.2002CB41250l)the National Natural Science Foundation of China(Grant Nos.90211006,30370257 and 30470280)the Knowledge Innovation Project of Institute of Geographical Sciences and Natural Resources Research,CAS(Grant No.CXIOG-E01-03-03).
文摘The Tibetan Plateau is characterized by lower atmospheric pressure, lower air temperature and high daily and seasonal variation due to high elevation. The photosynthesis of aaplants is significantly influenced by these alpine environmental factors. Apparent quantum yield (αA) is one of the basic parameters of photosynthesis and mass production. Its accuracy determination is of significance to model photosynthesis of C3 plants and global change on the plateau. In the Lhasa Plateau Ecological Station with 65.4 kPa of atmospheric pressure at an elevation of 3688 m, Li-Cor 6400 portable photosynthesis system was used to measure light response curves of winter wheat in different temperatures and intercellular CO2 concentration (C,). The slope of light response curve in weak light area of PFD from 0 to 150 μmol m-2 s-1 was used to evaluate the value of αA. The dependence of αA on temperature and intercellular concentration was analyzed. In 30℃, the average value of αA was 0.0476±0.0038. It is not quite different from the values in low elevation areas. αA is influenced both by temperature and by the ratio of CO2 and O2 partial pressure ([CO2]/[O2]). The measured values in the previous study were much lower. This might be due to systematic errors from instrument and data processing methods. The values of αA decreased linearly with temperature. It decreased 0.0007 in every 1℃ increase of temperature. The decrease slope is similar to those of C3 plants in the previous researches. While [O2] is constant,αA increases with Ciwith a hyperbolic relationship. In comparison with low elevation areas, the αA on the Tibetan Plateau is more sensitive to increase of CO2.
文摘研究采用目前先进的光合作用测定系统L i-Cor-6400测定濒危物种西藏巨柏的光合作用,自然环境条件下的西藏巨柏光合日进程表现为单峰型曲线,在12:00时左右达到最高峰,其光合作用不存在“午休现象”。在12:00时,西藏巨柏的气孔限制值和水分饱和亏缺分别达到最大值,此时的水分利用效率较高,在9:00时,西藏巨柏获得一天中最大的表观量子效率,水分利用效率达到最大值。其蒸腾速率在13:00时最大,这个时间并不与光合速率最大值同步,这说明在西藏特殊的气候环境条件下,影响光合速率的因素很多。在光合速率的日进程中,高光合速率值(大于4.00μm o lCO2/(m2.s))持续时间在5h左右,这使得西藏巨柏的光合作用产物得以有效积累,也为西藏巨柏在半干旱环境中的生长创造了有利条件。
