Examination on Processes and Mechanisms Involved in Carbon Dynamics in an Alpine Meadow on the Qinghai-Tibetan Plateau

青藏高原是世界上最高的高原。高原主要由高寒草原覆盖，在该地区的碳收支中起着重要作用。高原的特点是高辐照度、低气压和低温。为了研究高原草地生态系统的碳动态，建立了高寒草地碳动态模型（CDMag）。CDMag由包含光抑制模拟的总光合作用（Ac）子模型、考虑自养和异养呼吸的生态系统呼吸（ER）子模型和细胞间CO_2分压和冠层电导子模型组成。通过光抑制模拟来描述高寒生态系统对高辐照度环境的响应，采用多层辐照度转移方案来估计草木冠层内受光照和遮荫叶片的辐照度，并结合耦合的冠层，将更多的电导-净光合作用函数纳入Ac子模型。利用CDMag对青藏高原分布最广泛的高寒草地——矮嵩草草甸生态系统的碳动态进行了模拟。CDMag很好地描述了2001 ~ 2003年利用涡旋协方差方法获得的净生态系统交换（NEE）和夜间ER的日变化和季节变化。3年的NEE平均值约为1.62 μmol m^<-2>s^<-1>；实测NEE与模拟NEE的平均偏差为-0.16 ~ 0.33 μmol m^<-2> s^<-1>。由于光抑制作用，日总光合作用损失约5.3% ~ 5.6%。损失的主要原因是上冠层受光照叶片的Ac减少了7.5% ~ 7.8%。此外，高寒草甸光能利用效率具有季节动态特征，在生长季中期达到最高值。我们将CDMag推广到整个高原其他高寒草原。此外，青藏高原的高紫外线照射也会影响光合作用对CO_2的吸收。结果表明，在长时间人工增强UV-B辐射后，光合CO_2吸收速率和光合O_2演化速率均未发生显著变化。然而，吸收UV-B的化合物，在300 mm处的吸光度检测，似乎在增强UV-B照射后增加。高UV-B辐射下，高寒植物叶片生化成分（包括叶绿素和其他色素）和叶片厚度均显著增加，表明高寒植物改变了叶片形态和生化特征，以避免在高UV-B辐射下co2吸收的显著减少。少

The Qinghai-Tibetan Plateau is the highest plateau in the world. Covering mainly by alpine grasslands, the plateau plays an important role in the region's carbon budget. The plateau is characterized by high irradiance, low atmospheric pressure, and low temperature. To examine the carbon dynamics of grassland ecosystems on the plateau, we developed a new simulation model, the carbon dynamics model for alpine grasslands (CDMag). CDMag is composed of a gross photosynthesis (Ac) submodel including pbotoinhibition simulation, an ecosystem respiration (ER) submodel that considers both autotrophic and heterotrophic respiration, and an intercellular CO_2 partial pressure and canopy conductance submodel. A photoinhibition simulation is included to describe the gross production of alpine ecosystems in response to the high-irradiance environment A multilayered irradiance transfer scheme is adopted to estimate the irradiance on sunlit and shaded leaves within grassy canopies, and a coupled canopy … More conductance - net photosynthesis function is integrated into the Ac submodel. CDMag was used to simulate the carbon dynamics of the most extensively distributed alpine grassland, a Kobresia meadow ecosystem on the Qinghai-Tibetan Plateau. CDMag described well the diurnal and seasonal variation of net ecosystem exchange (NEE) and nighttime ER data obtained from 2001 to 2003 using the eddy-covariance method. The mean measured NEE was about 1.62 μmol m^<-2>s^<-1> for the measured periods of the 3 years ; the mean of the deviations between measured and simulated NEE was -0.16 to 0.33 μmol m^<-2> s^<-1>. Owing to photoinhibition, daily gross photosynthesis lost about 5.3%-5.6%. The losses were mainly contributed by the 7.5%-7.8% reduction in Ac of sunlit leaves of the upper canopy layer. In addition, the light-use efficiency of the alpine meadow had seasonal dynamics, with the highest values in the middle of the growing season. We have generalized CDMag for other alpine grasslands on the entire plateau.In addition, high UV irradiation on the Qinghai-Tibetan plateau could also affect photosynthetic CO_2 uptake. We found that neither the photosynthetic CO_2 uptake rate nor the photosynthetic O_2 evolution rate changed significantly after a long period of artificially enhanced UV-B radiation. However, UV-B-absorbing compounds, detected by absorbance at 300 mm, seemed to increase after enhanced UV-B irradiation. Both biochemical components including chlorophyll and other pigments, and leaf thickness increased significantly under high UV-B radiation, suggesting that these alpine plants changed their leaf morphology and biochemistry to avoid a significant decrease in CO_2 uptake under UV-B elevation. Less