Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems

We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m^–2 y^–1) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.     

春兰内生真菌的分离及其抑菌活性的初步研究

利用内蒙古锡林浩特国家气候观象台1994～2009年牧草生长季逐月实测资料,对CENTURY模型进行检验,模拟内蒙古典型草原1953～2010年间地上净初级生产力（ANPP）动态,并与26个气象因子进行相关性分析。模型检验结果显示,模拟值与观测值之间的相关系数为R²=0.66,斜率b=0.95,误差平方根值为50.51 g·m^-2,平均绝对百分比误差为44.19%。结果表明：（1）CENTURY模型能比较准确地模拟这类草原的季节动态和年际变化;在过去的58年中,内蒙古典型草原温度增加,降水减少,ANPP下降;ANPP变化趋势与降水量相似。（2）用实际气象观测资料模拟获得的ANPP随气温和降水的变化呈现出明显的变化规律,生长季内地上生物量对降水和温度的季节性分布也非常敏感;相关分析进一步表明,ANPP对生长季内降水量和极端高温非常敏感,而与年极端最低气温、平均地面温度、日照时数、平均风速和最大积雪深度无显著相关关系;过去58年研究区ANPP下降是降水减少、温度升高以及干旱事件频发共同作用的结果。（3）根据预测,在SRES B2情景下,未来50～100年内蒙古典型草原生长季平均最高气温和最低气温都将呈升高趋势,2080s分别升高4.01℃、4.35℃,每10年增加速率分别为0.35℃和0.38℃;降水量略呈增加,2020s、2050s和2080s研究区生长季将分别增加3.17%、5.13%和7.03%,每10年增加速率为0.09 mm;ANPP呈下降趋势年际间波动较大,2020s、2050s和2080s研究区将分别下降5.76%、7.52%和11.42%,每10年下降速率为0.76 g·m^-2。     

基于CENTURY模型模拟火烧对大兴安岭兴安落叶松林碳动态的影响

火作为森林生态系统重要的自然干扰因子之一,对森林的碳动态有着不可忽视的影响.本研究使用CENTURY模型模拟了大兴安岭呼中林区兴安落叶松林的碳收支对不同强度火烧的响应.结果表明:在不同强度火烧后,土壤总碳库呈先升后降再逐渐恢复的变化趋势,而林分生物碳库则先降后升,其中,林分细小组分碳库的恢复速度明显快于大组分,各碳库的波动程度随火烧强度的增大而增大.森林植被的净初级生产力(NPP)和土壤异养呼吸在火后均先降后升,但NPP的恢复快于土壤异养呼吸,二者的动态变化改变了林分的碳源/汇作用.轻微火烧后,兴安落叶松林仍表现为弱碳汇,并很快恢复到火前水平;其他强度的火烧使兴安落叶松林在短期内(9～12年)表现为碳源,随后逐渐转为碳汇.较低强度的林火不仅可以促进落叶松林的更新、减少死可燃物,也不会对林分的碳汇功能造成太大影响;高强度的严重林火对土壤和林木碳库造成严重损失,延缓森林的恢复,并可使林分表现为较长时间的碳源.     

Carbon balance along the Northeast China Transect (NECT-IGBP)

The Northeast China Transect (NECT) along a precipitation gradient was used to cal-culate the carbon balance of different vegetation types, land-use practices and temporal scales. NECT consists of mixed coniferous-broadleaved forest ecosystems, meadow steppe ecosystemsand typical steppe ecosystems. Analyses of the C budget were carried out with field measurement based on dark enclosed chamber techniques and alkali absorption methods, and the application of the CENTURY model. Results indicated that: (1) soil CO_2 flux had a strong diurnal and seasonal variation influenced by grassland type and land-use practices. However, the seasonal variation on soil CO_2 fluxes did not show obvious changes between non-grazing and grazing Leymus chinensis dominated grasslands. (2) Hourly soil CO_2 fluxes mainly depended on temperature, while dailyCO_2 fluxes were affected both by temperature and moisture. (3) NPP of the three typical ecosys-tems showed linear relationships with inter-annual precipitation, but total soil carbon of those eco-systems did not. NPP and total soil carbon values decreased westward with decreasing precipita-tion. (4) Model simulation of NPP and total soil carbon showed that mean annual precipitation was the major limiting factor for ecosystem productivity along NECT. (5) Mean annual carbon budget is the largest for the mixed coniferous- broadleaved forest ecosystem (503.2 gC m~(-2)a~(-1)), followed bythe meadow steppe ecosystem (227.1 gC m~(-2)a~(-1)), and the lowest being the typical steppe eco-system (175.8 gC m~(-2)a~(-1)). This study shows that concurrent field measurements of terrestrial ecosystems including the soil and plant systems with surface layer measurements along the wa-ter-driven IGBP-NECT are valuable in understanding the mechanisms driving the carbon cycle in different vegetation types under different land-use practices. Future transect research should be emphasized.     

兴安落叶松林碳平衡及管理活动影响研究 （英文）

 在利用大兴安岭地区根河落叶松(Larix gmelini)林生态系统定位研究站的实际观测资料验证CENTURY模型的基础上,探讨了林业经营管理方式对兴安落叶松林碳循环的影响,指出：1）目前兴安落叶松林是一个碳汇,每年净吸收碳2.65 t·hm-2。2）砍伐将使兴安落叶松林生物量和生产力下降,土壤碳含量则有所增加。干扰强度越大则其植物总生物量、生产力和土壤碳含量变化幅度越大,伐后恢复时间也越长。3）连年去除枯枝落叶处理使兴安落叶松林土壤碳含量下降,土壤越来越贫瘠。植物总生物量在前30年迅速增加,之后则趋于稳     

Influence of spatially dependent,modeled soil carbon emission factors on life‐cycle greenhouse gas emissions of corn and cellulosic ethanol

Converting land to biofuel feedstock production incurs changes in soil organic carbon (SOC) that can influence biofuel life‐cycle greenhouse gas (GHG) emissions. Estimates of these land use change (LUC) and life‐cycle GHG emissions affect biofuels' attractiveness and eligibility under a number of renewable fuel policies in the USA and abroad. Modeling was used to refine the spatial resolution and depth extent of domestic estimates of SOC change for land (cropland, cropland pasture, grassland, and forest) conversion scenarios to biofuel crops (corn, corn stover, switchgrass, Miscanthus, poplar, and willow) at the county level in the USA. Results show that in most regions, conversions from cropland and cropland pasture to biofuel crops led to neutral or small levels of SOC sequestration, while conversion of grassland and forest generally caused net SOC loss. SOC change results were incorporated into the Greenhouse Gases, Regulated Emissions, and Energy use in Transportation (GREET) model to assess their influence on life‐cycle GHG emissions of corn and cellulosic ethanol. Total LUC GHG emissions (g CO₂eq MJ^?1) were 2.1–9.3 for corn‐, ?0.7 for corn stover‐, ?3.4 to 12.9 for switchgrass‐, and ?20.1 to ?6.2 for Miscanthus ethanol; these varied with SOC modeling assumptions applied. Extending the soil depth from 30 to 100 cm affected spatially explicit SOC change and overall LUC GHG emissions; however, the influence on LUC GHG emission estimates was less significant in corn and corn stover than cellulosic feedstocks. Total life‐cycle GHG emissions (g CO₂eq MJ^?1, 100 cm) were estimated to be 59–66 for corn ethanol, 14 for stover ethanol, 18–26 for switchgrass ethanol, and ?7 to ?0.6 for Miscanthus ethanol. The LUC GHG emissions associated with poplar‐ and willow‐derived ethanol may be higher than that for switchgrass ethanol due to lower biomass yield.     

内蒙古典型草原地上净初级生产力对气候变化响应的模拟

利用内蒙古锡林浩特国家气候观象台1994～2009年牧草生长季逐月实测资料,对CENTURY模型进行检验,模拟内蒙古典型草原1953～2010年间地上净初级生产力(ANPP)动态,并与26个气象因子进行相关性分析。模型检验结果显示,模拟值与观测值之间的相关系数为R2=0.66,斜率b=0.95,误差平方根值为50.51g.m-2,平均绝对百分比误差为44.19%。结果表明:(1)CENTURY模型能比较准确地模拟这类草原的季节动态和年际变化;在过去的58年中,内蒙古典型草原温度增加,降水减少,ANPP下降;ANPP变化趋势与降水量相似。(2)用实际气象观测资料模拟获得的ANPP随气温和降水的变化呈现出明显的变化规律,生长季内地上生物量对降水和温度的季节性分布也非常敏感;相关分析进一步表明,ANPP对生长季内降水量和极端高温非常敏感,而与年极端最低气温、平均地面温度、日照时数、平均风速和最大积雪深度无显著相关关系;过去58年研究区ANPP下降是降水减少、温度升高以及干旱事件频发共同作用的结果。(3)根据预测,在SRES B2情景下,未来50～100年内蒙古典型草原生长季平均最高气温和最低气温都将呈升高趋势,2080s分别升高4.01℃、4.35℃,每10年增加速率分别为0.35℃和0.38℃;降水量略呈增加,2020s、2050s和2080s研究区生长季将分别增加3.17%、5.13%和7.03%,每10年增加速率为0.09mm;ANPP呈下降趋势年际间波动较大,2020s、2050s和2080s研究区将分别下降5.76%、7.52%和11.42%,每10年下降速率为0.76g.m-2。     

Carbon balance along the Northeast China Transect(NECT-IGBP)

The Northeast China Transect (NECT) along a precipitation gradient wasused to calculate the carbon balance of different vegetation types, land-use practices and temporal scales. NECT consists of mixed coniferous-broadleaved forest ecosystems, meadow steppe ecosystems and typical steppe ecosystems. Analyses of the C budget were carried out with field measurement based on dark enclosed chamber techniques and alkali absorption methods, and the application of the CENTURY model. Results indicated that: (1) soil CO2 flux had a strong diurnal and seasonal variation influenced by grassland type and land-use practices. However, the seasonal variation on soil CO2 fluxes did not show obvious changes between non-grazing and grazing Leymus chinensis dominated grasslands. (2) Hourly soil CO2 fluxes mainly depended on temperature, while daily CO2 fluxes were affected bothby temperature and moisture. (3) NPP of the three typical ecosystems showed linear relationships with inter-annual precipitation, but total soil carbon of those ecosystems did not. NPP and total soil carbon values decreased westward with decreasing precipitation. (4) Model simulation of NPP and total soil carbon showed that mean annual precipitation was the major limiting factor for ecosystem productivity along NECT. (5) Mean annual carbon budget is the largest for the mixedconiferous- broadleaved forest ecosystem (503.2 gC m-2 a-1), followed by the meadow steppe ecosystem (227.1 gC m-2 a-1), and the lowest being the typical steppe ecosystem (175.8 gC m-2 a-1). This study shows that concurrent field measurements of terrestrial ecosystems including the soil and plant systems with surface layer measurements along the water-driven IGBP-NECT are valuable in understanding the mechanisms driving the carbon cycle in different vegetation types under different land-use practices. Future transect research should be emphasized.     

基于CENTURY模型研究干旱区人工绿洲开发与管理模式变化对土壤碳动态的影响

近半个世纪前,中国西北干旱区人类大规模的水土开发活动使得流域下部的荒漠覆被土地转变成了人工绿洲,强烈的人类耕作活动使得人工绿洲土壤有机碳库发生了显著变化。以干旱区典型的三工河流域下部的人工绿洲为例,基于CENTURY模型,研究人工绿洲开发前后及农业管理模式变化对表层土壤有机碳库(0-20cm)的影响。CENTURY模型模拟结果表明:(1)研究区荒漠灌木林地开垦为人工绿洲后,在最初的2a土壤总有机碳(TOC)快速增加,随后呈逐渐下降的趋势;(2)研究区人工绿洲在被开发后50a的连续耕作下,平均土壤TOC呈先增后减再增的"N"型变化趋势,但最终土壤TOC超过了原始自然状态下的TOC,而且2008年土壤TOC比原始荒漠状态增加7.74%,说明研究区表层土壤有机碳总体呈"碳汇"趋势。尤其在研究区实施了免耕、秸秆粉碎还田、科学测土配方施肥等保护性耕作措施后,土壤固碳效应明显,这完全不同于热带森林、中国北部温带半干旱草原及非洲Savanna半干旱稀树草原开垦为耕地后土壤有机碳大量损失的结论。     

21世纪上半叶内蒙古草地植被净初级生产力变化趋势

基于中国气象局国家气候中心新发布的中短期适应气候变化的新情景(RCP4.5)和极端情景(RCP8.5)下的气候预估数据,采用空间化后的CENTURY模型模拟探讨2011－2050年内蒙古草地植被净初级生产力(NPP)的时空变化特征.结果表明: 区域尺度上,未来气候变化情景下内蒙古草地NPP年下降速率分别为0.57 g C·m^-2·a^-1(RCP4.5)、0.89 g C·m^-2·a^-1(RCP8.5);相对于基准时段,RCP4.5情景下内蒙古草地NPP在2020s、2030s、2040s分别下降11.6%、12.0%、18.0%,而RCP8.5情景下降幅分别为23.8%、21.2%、30.1%.不同气候情景下内蒙古草地NPP时空变化特征差异较大,但即使在RCP4.5下未来40年绝大部分草地NPP也将呈现下降趋势,15.6%的草地减产超过20%.这表明未来气候变化情景下内蒙古草地降水略增的态势不足以补偿因温度升高对草地植被初级生产力所产生的负面作用,草地资源的可持续发展将面临更大挑战.