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.

AbstractCarbon通过单个过程，光合作用进入生态系统，并且几乎所有过程都通过呼吸返回到大气中，其中约50-80％发生在地下。土壤呼吸整合了根代谢和分解生物的活性。虽然已知影响植物代谢（自养）呼吸和分解率（异养呼吸）的主要过程，但预测时空和时间的土壤呼吸变化的能力是有限的 - 当前和未来的碳循环中的主要不确定性。这里提出的工作将结合新的测量和建模方法，用于分离自养和异养的呼吸，并确定C呼吸的C年龄。在跨越一系列北美生物群落和气候的Ameriflux网络中的现场地点，这些方法将包括：（1）频繁，自动化，土壤呼吸的测量以及相关因素； （2）基于稳定同位素和放射性CO2中稳定同位素的测量方法的同位素质量平衡方法； （3）孵育以确定异养呼吸成分对不断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水分含量。产生的数据将用于将土壤呼吸C分配为自养和异养成分，以确定异养呼吸的C的年龄，并确定有助于其生产的土壤有机物的成分，并确定这些关系的机会如何控制变量（光合作用率，土壤条件，等）。结果将用于参数化CASA生态系统模型的纽约营养性呼吸成分，并测试该模型在季节性到年际时间表上的异养呼吸源的平衡。 CASA模型的预测将在跨越（1）升级的区域梯度和（2）从热带森林到苔原的一套地点进行进一步测试。我们将使用C同位素（全球网络站点的13C和14C在阿拉斯加的Barrow，Alaska Pointeric CO2中的13C）的季节性变化的大气记录，作为CASA模型确定季节性与北半球陆地生态系统和大气之间的CASA季节性交换的能力的全球测试。分离生态系统呼吸的组成部分是生态系统科学中重要的研究挑战之一。该活动将使用新工具，尤其是在测量和模型中对放射性碳示踪剂的创新使用，以在选定的Ameriflux站点对C通量的过程水平理解。这项工作将进一步了解陆地生态系统如何影响全球碳循环，并通过展示异性营养呼吸将如何响应温度和水分的变化来改善未来大气浓度的二氧化碳的预测。我们的计划通过W.M.凯克碳循环加速器质谱设施将训练下一代科学家在放射性碳的应用中研究土地和海洋C循环。