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: 0223188
• 负责人: Eric Davidson
• 金额: $ 12.45万
• 依托单位: Woodwell Climate Research Center, Inc.
• 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 2005-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0223188&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.

摘要 碳通过光合作用这一单一过程进入生态系统，几乎所有碳都通过呼吸返回到大气中，其中约 50-80% 发生在地下。土壤呼吸整合了根系代谢和分解生物的活动。虽然影响植物代谢（自养）呼吸和分解速率（异养呼吸）的主要过程是已知的，但预测土壤呼吸在空间和时间上的变化的能力是有限的——这是当前和未来碳循环的主要不确定性。这里提出的工作将结合新的测量和建模方法来分离自养和异养呼吸，并确定从土壤中呼吸的 C 的年龄。在跨越一系列北美生物群落和气候的 Ameriflux 网络现场，这些方法将包括：(1) 频繁、自动化地测量土壤呼吸和相关因素； (2) 基于呼吸二氧化碳中稳定同位素和放射性碳测量的同位素质量平衡方法； (3) 培养以确定异养呼吸成分对土壤条件变化的反应； (4) 在一些地点，通过排除降雨来控制土壤湿度。生成的数据将用于将土壤呼吸碳划分为自养和异养成分，确定异养呼吸碳的年龄并识别有助于其生产的土壤有机质成分，并确定这些关系如何与控制变量（光合作用速率、土壤条件等）发生变化。结果将用于参数化 CASA 生态系统模型的新自养呼吸组成部分，并测试该模型在季节到年际时间尺度上预测异养呼吸来源平衡的效果。 CASA 模型的预测将在跨越 (1) 气候层序和 (2) 从热带森林到苔原的一系列地点的区域梯度上进行进一步测试。我们将使用 C 同位素季节变化的大气记录（全球网络站点的 13C 和阿拉斯加州巴罗角大气 CO2 的 14C）作为 CASA 模型确定北半球陆地生态系统和大气之间 C 的季节到年际交换的能力的全球测试。智力价值。分离生态系统呼吸的组成部分是生态系统科学中最重要的研究挑战之一。这项活动将使用新工具，特别是在测量和模型中创新地使用放射性碳示踪剂，以在选定的 Ameriflux 地点对 C 通量进行过程层面的了解。产生更广泛的影响。这项工作将增进对陆地生态系统如何影响全球碳循环的基本了解，并将通过展示异养呼吸如何响应温度和湿度的变化来改进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来教育学生。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来研究陆地和海洋碳循环。