内蒙古典型草原不同群落净生态系统生产力的动态变化

Net ecosystem productivity dynamics of grassland communities on the typical steppe of Inner Mongolia

净生态系统生产力(net ecosystem productivity,NEP)是反映生态系统碳源汇功能的重要指标。本研究选取内蒙古锡林河流域的贝加尔针茅群落、大针茅群落、克氏针茅群落和羊草群落为对象,利用BIOME-BGC模型模拟了4个草地群落年际间和年内逐日NEP动态变化,分析了4个草地群落对降水量的响应特征和可能机制,并且探讨气候变化背景下4个草地群落水分胁迫系数、降水利用率和碳转化效率的变化规律。结果表明:1954—2012年贝加尔针茅群落、大针茅群落、克氏针茅群落和羊草群落的多年平均NEP分别为11.41、-7.82、-5.03和9.30 g C·m-2·a-1。总体来看,4种草地群落多年平均日NEP的年内季节动态均呈先释放、后固碳、再释放的变化特征。4种草地群落多年平均水分胁迫系数由高到低分别为:贝加尔针茅>羊草>大针茅>克氏针茅;多年平均降水利用效率由高到低分别为:贝加尔针茅>克氏针茅>大针茅>羊草;多年平均碳素转化效率由高到低分别为:贝加尔针茅>克氏针茅>大针茅>羊草。4种草地群落NEP与年降水量均存在显著的相关性,NEP为0时,4种草地群落年降水量平均值为295.76 mm,说明在年降水量大于该值时NEP多为正值,而小于该值时NEP多为负值。

The net ecosystem productivity （NEP） is an important indicator to reflect the carbon budget of ecosystems. Our objective was to probe the NEP dynamic pattern and its response to climate change on the typical steppe in Inner Mongolia to better understand mechanisms of grassland carbon budget. BIOMEBGC model was used to simulate the NEP dynamics of four grassland communities in Xilingol River Basin by using the ecophysiological parameters according to the reference and the daily climate data simulated by MT-CLIM model as inputs. The water stress index （WSI）, rain use efficiency （RUE） and carbon sequestration efficiency （CSE） were calculated based on other model outputs, including evapotranspiration （ET）, net primary productivity （NPP） and gross primary productivity （GPP）. During 1954 to 2012, the multiyear average NEP of Stipa baicalensis, S. grandis, S. krylovii and Leymus chinensis communities was 11.41, -7.82, -5.03 and 9.30 g C·m-2·a-1, respectively. NEP seasonally exhibited a pattern of releasing CO2-sequestrating CO2-releasing CO2 in a year. The order of multiyear average was S. baicalensis 〉 L. chinensis 〉 S. grandis 〉 S. krylovii for WSI, S. baicalensis 〉 S. krylovii 〉 S. grandis 〉 L. chinensis for RUE, and S. baicalensis 〉 S. krylovii 〉 S. grandis 〉 L. chinensis for CSE. There was a close relationship between NEP and precipitation, and the correlations were at an extremely significant level in S. grandis, S. krylovii and L. chinensis communities. NEP turned from being negative to being positive when the annual precipitation of the four grassland communities was greater than 295.76 mm.