IRCEB: Interannual Climate Variability and Ecosystem Processes: A Quantitative Assessment Combining Modeling with Field and Mesocosm Experiments

0078325Arnone 众所周知，大气CO2正在上升，大气CO2的变化很可能影响地球气候，气候变化导致净生态系统生产力（NEP，生态系统碳交换的衡量标准）的变化，陆地生态系统充当大气CO2的调节机制。尽管相关研究表明大气CO2、气候和NEP之间存在紧密联系，但事实是我们无法明确量化它们之间的联系和反馈。这也许是我们知识中最关键的空白，使得预测全球环境变化的速度和后果变得困难甚至不可能。该IRCEB项目由三个组成部分组成——在独特的中宇宙设施中进行综合实验、现场实验以及统计和模拟建模——这将使研究人员能够明确检验关于气候、大气二氧化碳和NEP之间关系的四个假设：（1）在异常温暖的年份中观察到的全球大气二氧化碳的快速上升是由于异养呼吸（Rh）增加导致温度引起的NEP下降所致； (2) 受刺激的 Rh 还会导致氮矿化增加，导致土壤有效氮库增加，进而导致植物氮吸收和储存增加； (3) 暖年后，气温和Rh水平恢复正常，加上植物氮储存量高导致NPP增加，将导致NEP大幅增加； (4) 极端温度会在不同时间尺度引起多种生态反应，并反馈影响 NEP，从而影响大气 CO2。其他反馈也将得到测试。该研究的核心是在沙漠研究所的中宇宙规模 EcoCELL 蒸渗仪实验室中进行的一项实验。该设施能够在生态系统规模上连续测量 NEP，同时控制气候变量。 EcoCELL 实验涉及在实验的第二年将环境温度提高 4OC，结合一系列具体测量来量化控制碳循环的生理过程，将使研究人员能够了解 NEP 如何响应逐年的温度变化。高草草原是世界上研究最多的草原生态系统之一，为该项目提供了一个生态系统模型；完整的土壤植物巨石将从草原现场提取并运输到 EcoCELLS，为实验室测试提供基础。EcoCELL 实验将与其他两个研究部分相关联，即现场本地高草草原实验和建模数据合成。高草草原实地研究将有助于校准和衡量受控环境下观察到的反应，并测试温度引起的土壤水分和养分可用性影响的因果关系，假设这是温度引起的 NEP 变化的关键因素。这些实验将有助于确定温度变化是否通过直接影响、对水可用性的影响或对营养动态的影响来影响高草草原生态系统的碳交换。统计分析和两个特定模型将代表一系列技术，用于识别控制生态系统对温度异常响应的过程，并允许理解和发展实验室和现场实验之间的联系。

0078325ArnoneIt is well known that atmospheric CO2 is rising, that changes in atmospheric CO2 are likely to affect the earth's climate, that changes in climate cause changes in net ecosystem productivity (NEP, a measure of ecosystem carbon exchange), and that terrestrial ecosystems act as a regulatory mechanism for atmospheric CO2. Although correlative studies have demonstrated that there are tight connections between atmospheric CO2, climate, and NEP, the fact is that we cannot explicitly quantify the links and feedbacks among them. This is perhaps the most critical void in our knowledge making it difficult, if not impossible, to predict the rate and consequences of global environmental change. This IRCEB project has three components - integrating experiments in a unique mesocosm facility, field experiments, and statistical and simulation modeling - that will allow the investigators to explicitly test four hypotheses regarding the relationships among climate, atmospheric CO2 and NEP: (1) an observed rapid rise in global atmospheric CO2 in anomalously warm years results from temperature-induced decreases in NEP resulting from increased heterotrophic respiration (Rh); (2) stimulated Rh will also lead to increased N mineralization causing increases in available soil N pools which in turn will result in increased plant N uptake and storage; (3) following the warm year, a return to more normal temperatures and Rh levels, along with high plant N stores causing an increase in NPP, will result in a large increase in NEP; and (4) temperature extremes will cause a multitude of ecological responses at different time scales and feedback to affect NEP, and therefore atmospheric CO2. Other feedbacks will be tested, as well.The centerpiece of the study is an experiment to be conducted in the mesocosm-scale EcoCELL lysimeter laboratory at the Desert Research Institute. This facility has the capability to continuously measure NEP on an ecosystem scale while simultaneously controlling climate variables. The EcoCELL experiment involves the imposition of a 4OC increase in ambient temperature during the second year of the experiment, which combined with an array of specific measurements to quantify physiological processes that control the carbon cycle, will enable the investigators to understand how NEP responds to year-to-year variation in temperature. Tallgrass prairie, one of the world's most studied grassland ecosystems, provides a model ecosystem for the project; and intact soil-plant monoliths will be extracted from a prairie field site and transported to the EcoCELLS providing the basis for the laboratory test.The EcoCELL experiment will be linked to two other study components, a native tallgrass prairie experiment in the field and modeling-data synthesis. The tallgrass prairie field study will help to calibrate and scale the observed responses under controlled environments and test causal relationships of temperature-induced effects on the availability of soil moisture and nutrients, hypothesized to be key factors in temperature-induced changes in NEP. These experiments will help determine whether variation in temperature affects tallgrass prairie ecosystem carbon exchange via direct effects, effects on water availability, or effects on nutrient dynamics. Statistical analysis and two specific model will represent a range of techniques to identify the processes that control ecosystem responses to temperature anomalies, and allow understanding and development of linkages between the laboratory and field experiments.