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

众所周知，大气二氧化碳正在上升，大气二氧化碳的变化可能会影响地球气候，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，以及陆地生态系统对大气二氧化碳的调节机制。虽然相关研究表明，大气CO2、气候和NEP之间存在密切联系，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，使得预测全球环境变化的速度和后果变得困难，如果不是不可能的话。这个IRCEB项目有三个组成部分--一个独特的中观设施中的综合实验、田间实验以及统计和模拟模型--这将使研究人员能够明确地检验关于气候、大气CO2和NEP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CO2的快速上升是由于温度导致异养呼吸(Rh)增加导致NEP下降；(2)刺激Rh还将导致N矿化增加，从而增加土壤有效N库，这反过来将导致植物N的吸收和储存增加；(3)在温暖的一年后，温度和相对湿度恢复到更正常的水平，以及较高的植物N贮量导致NPP的增加，将导致NEP的大幅增加；(4)极端温度将导致不同时间尺度和反馈的多种生态响应，从而影响NEP，从而影响大气CO2。这项研究的中心是将在沙漠研究所的中尺度EcoCELL蒸渗仪实验室进行的一项实验。该设施有能力在生态系统范围内连续测量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4摄氏度，结合一系列具体的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如何应对温度的年复一年变化。高草草原是世界上研究最多的草原生态系统之一，它为该项目提供了一个模型生态系统；完整的土壤-植物整体将从草原现场提取并运输到EcoCELLS，为实验室测试提供基础。EcoCELL实验将与另外两个研究部分联系起来，即田间本地高粱草原实验和模型数据合成。Tallgras草原田间研究将有助于校准和衡量在受控环境下观测到的反应，并测试温度诱导对土壤水分和养分有效性的影响的因果关系，这被认为是温度诱导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、水可获得性或营养动态影响Tallgras草原生态系统碳交换。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，并使人们能够了解和发展实验室和实地实验之间的联系。

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.