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。该高原主要由高山草原覆盖，在该地区的碳收支中发挥着重要作用。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，我们开发了一个新的模拟模型，高寒草地碳动态模型（CDMag）。CDMag模型由包含光合抑制模拟的总光合作用（Ac）子模型、同时考虑自养和异养呼吸的生态系统呼吸（ER）子模型、胞间CO_2分压和冠层电导率子模型组成。本文采用光抑制模拟的方法来描述高山生态系统对高光照环境的总生产力响应。采用多层辐射传输方案来估算草地冠层内阳光照射和遮荫叶片上的辐射，以及耦合的冠层。 ...更多信息 电导-净光合作用函数被集成到Ac子模型中。利用CDMag模拟了青藏高原分布最广的高寒草地--嵩草草甸生态系统的碳动态。CDMag较好地描述了2001 - 2003年利用涡动协方差方法获得的净生态系统交换（NEE）和夜间ER数据的日变化和季节变化。在3年的测量期间，平均测量的NEE约为1.62 μmol m^<-2>s^<-1>;测量和模拟NEE之间的平均偏差为-0.16至0.33 μmol m^<-2>s^<-1>。由于光抑制，日总光合量损失约5.3%-5.6%。冠层上部受阳光照射的叶片Ac减少7.5%~ 7.8%是造成损失的主要原因。高寒草甸光能利用效率具有季节动态，在生长季中期最高。此外，青藏高原高紫外线辐射也会影响光合CO_2吸收。结果表明，在长时间的人工增强UV-B辐射下，光合CO_2吸收速率和光合O_2释放速率均未发生显著变化。然而，UV-B-吸收化合物，在300毫米处的吸光度检测，增强UV-B照射后，似乎增加。高UV-B辐射下，高山植物叶片的叶绿素和其他色素含量以及叶片厚度均显著增加，表明这些高山植物改变了叶片的形态和生化特性，以避免UV-B辐射对CO2吸收的显著影响。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