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

[00:78 . 325]众所周知，大气CO2正在上升，大气CO2的变化可能影响地球气候，气候变化引起生态系统净生产力（NEP，一种衡量生态系统碳交换的指标）的变化，而陆地生态系统对大气CO2起着调节机制的作用。虽然相关研究表明大气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。这可能是我们知识中最关键的空白，使我们很难（如果不是不可能的话）预测全球环境变化的速度和后果。这个IRCEB项目有三个组成部分——在一个独特的中大气设施中进行综合实验、实地实验以及统计和模拟建模——这将使研究人员能够明确地检验关于气候、大气二氧化碳和新能源p之间关系的四个假设：(1)在异常温暖的年份，观测到的全球大气二氧化碳的快速上升是由异养呼吸（Rh）增加引起的温度引起的新能源p减少造成的；(2)受刺激的Rh还会导致N矿化增加，导致土壤有效氮库增加，进而导致植物对N的吸收和储存增加；(3)暖年之后，恢复到更正常的温度和Rh水平，加上植物N储量高导致NPP增加，将导致NEP大幅增加；(4)极端温度将引起不同时间尺度的多种生态响应和反馈，从而影响NEP，从而影响大气CO2。其他反馈也将被测试。这项研究的核心是在沙漠研究所的中尺度EcoCELL渗滤仪实验室进行的一项实验。该设施能够在控制气候变量的同时，在生态系统尺度上连续测量新经济价值。EcoCELL实验包括在实验的第二年将环境温度提高4摄氏度，并结合一系列具体的测量来量化控制碳循环的生理过程，这将使研究人员能够了解NEP如何应对每年的温度变化。高草草原是世界上研究最多的草地生态系统之一，为该项目提供了一个模型生态系统；完整的土壤-植物单体将从草原场地提取并运送到EcoCELLS，为实验室测试提供基础。EcoCELL实验将与另外两个研究组成部分相关联，一个是实地的高草草原实验，另一个是建模数据合成。高草草原野外研究将有助于校准和衡量在受控环境下观察到的响应，并测试温度诱导的土壤水分和养分有效性效应的因果关系，这些效应被假设为温度诱导的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、对水分有效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。统计分析和两个具体模型将代表一系列技术，以确定控制生态系统对温度异常反应的过程，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.