Collaborative Research: Climate controls over ecosystem respiration: Using isotopes to determine the sources and age of respired carbon

合作研究：气候对生态系统呼吸的控制：利用同位素确定呼吸碳的来源和年龄

• 批准号: 0223157
• 负责人: James Randerson
• 金额: $ 10.55万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-10-01 至 2003-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0223157&HistoricalAwards=false
• 关键词: Collaborative; Research; Climate; controls; over

ABSTRACTCarbon enters ecosystems through a single process, photosynthesis, and nearly all is returned to the atmosphere through respiration, some 50-80% of which occurs below ground. Soil respiration integrates root metabolism and the activity of decomposer organisms. While the major processes affecting plant metabolic (autotrophic) respiration and decomposition rates (heterotrophic respiration) are known, the ability to predict variations in soil respiration in space and time is limited - a major uncertainty in the current and future carbon cycle. The work proposed here will combine new measurement and modeling approaches for separating autotrophic and heterotrophic respiration, and determining the age of C respired from soils. At field sites in the Ameriflux network that span a range of North American biomes and climates, these methods will include: (1) frequent, automated, measurements of soil respiration and related factors; (2) isotope mass balance methods based on measurements of stable isotopes and radiocarbon in respired CO2; and (3) incubations to determine responses of heterotrophic respiration components to changing soil conditions; and (4) at some sites, manipulation of soil moisture content through rainfall exclusion. The data generated will be used to partition soil respired C into autotrophic and heterotrophic components, to determine the age of heterotrophically respired C and identify the components of soil organic matter contributing to its production, and to determine how these relationships chance with controlling variables(photosynthesis rate, soil conditions, etc). The results will be used to parameterize a newautotrophic respiration component of the CASA ecosystem model, and to test how well the model predicts the balance of sources of heterotrophic respiration on seasonal to interannual timescales. Predictions of the CASA model will be further tested across regional gradients spanning (1) a climosequence and (2) a suite of sites from tropical forest to tundra. We will use atmospheric records of seasonal variation in C isotopes (13C at the global network sites and 14C in atmospheric CO2 at Point Barrow, Alaska) as a global test of the CASA model's ability to determine the seasonal to interannual exchange of C between northern hemisphere terrestrial ecosystems and the atmosphere.Intellectual merit. Separating the components of ecosystem respiration is one of the fundamentally important research challenges in ecosystem science. This activity will use new tools, in particular, innovative use of the radiocarbon tracer in measurements and models, to develop process level understanding of C fluxes at selected Ameriflux sites.Broader impacts. This work will advance fundamental understanding of how terrestrial ecosystems influence the global carbon cycle, and will improve projections of future atmospheric concentrations of carbon dioxide by showing how heterotrophic respiration will respond to changes in temperature and moisture. Our program to educate students through a short course in radiocarbon at the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry facility will train the next generation of scientists in the applications of radiocarbon to study land and ocean C cycling.

碳通过光合作用进入生态系统，几乎所有的碳都通过呼吸作用返回大气，其中50-80%发生在地下。土壤呼吸综合了根系代谢和分解生物的活动。虽然影响植物代谢（自养）呼吸和分解率（异养呼吸）的主要过程是已知的，预测土壤呼吸在空间和时间上的变化的能力是有限的-在当前和未来的碳循环的一个主要的不确定性。本文提出的工作将结合联合收割机新的测量和建模方法，用于分离自养和异养呼吸，并确定从土壤中呼吸的C的年龄。在Ameriflux网络中横跨北美生物群落和气候范围的实地，这些方法将包括：（1）经常自动测量土壤呼吸作用和相关因素;（2）同位素质量平衡方法，以测量呼吸的CO2中的稳定同位素和放射性碳为基础;（3）培养，以确定异养呼吸作用成分对变化的土壤条件的反应;（4）在某些地点，通过排除降雨来操纵土壤含水量。所产生的数据将被用来划分土壤呼吸C到自养和异养组件，以确定异养呼吸C的年龄，并确定土壤有机质的组成部分，有助于其生产，并确定这些关系的机会与控制变量（光合速率，土壤条件等）。结果将被用来parametriums的CASA生态系统模型的neprototrophic呼吸组件，并测试如何以及该模型预测的平衡源的异养呼吸的季节到年际的时间尺度。CASA模型的预测将在跨越（1）气候序列和（2）从热带森林到苔原的一系列地点的区域梯度上进一步测试。我们将使用大气中碳同位素的季节性变化记录（全球网络站点的13 C和阿拉斯加州巴罗巴罗点大气CO2中的14 C）作为CASA模型确定北方陆地生态系统和大气之间碳的季节至年际交换能力的全球测试。生态系统呼吸组分的分离是生态系统科学研究的重要挑战之一。这项活动将使用新的工具，特别是在测量和模型中创新性地使用放射性碳示踪剂，以发展对选定的Ameriflux站点的C通量的过程水平的理解。这项工作将促进对陆地生态系统如何影响全球碳循环的基本理解，并将通过显示异养呼吸如何对温度和湿度变化作出反应，改善对未来大气二氧化碳浓度的预测。我们的计划是通过在W.M.的放射性碳短期课程教育学生。凯克碳循环加速器质谱设施将培训下一代科学家应用放射性碳研究陆地和海洋碳循环。