Collaborative Research: Experimental Studies of Ecosystem Responses to Elevated CO2: Interactions with Nitrogen, Water, and Species Characteristics

Drs。Field、Chapin和Mooney将对加州一年生草地对资源平衡改变的响应进行综合研究，重点研究控制生态系统对二氧化碳升高响应的因素。他们的研究包括协调经验和建模程序，以测试一系列假设，这些假设可能解释控制系统级行为的机制和反馈，这些机制和反馈控制着地上和地下的生产、分解和营养循环，以响应资源的变化。二氧化碳浓度升高的系统级效应的概念模型是基于系统级响应机制和直接效应位点的两个假设。首先，他们假设二氧化碳浓度升高可能会产生新的资源平衡，但植物生长的响应可以通过资源平衡中其他变化的响应来理解和预测，这些变化会改变碳的可用性，相对于其他资源。其次，他们假设系统水平对二氧化碳升高的反应主要是通过对植物的直接影响来驱动的。本研究项目由五个部分组成：1)研究自然生态系统对开顶箱中二氧化碳浓度升高的响应。2)利用开放式顶室人工微生态系统，探索生态系统对一系列变化的响应，包括二氧化碳浓度升高、养分和水分有效性改变以及物种组成改变。3)利用其他实验的凋落物和同位素示踪剂，通过室内、田间和微生态系统试验研究了分解和养分循环的控制因素。4)通过一系列温室试验探索资源对植物生长、分配和组织化学的影响。5)建立模型，整合实验结果，连接和扩展现有的生态系统、群落和植物模型。这个项目有潜力推进我们对全球气候变化的系统级响应的几个方面的理解。首先，加州一年生草地二氧化碳含量升高的研究将补充其他草原的二氧化碳研究，其结果来自一个独特的低碳储存和快速平衡系统。其次，植物的矮小，加上系统平衡的小时间常数，将使研究人员能够探索广泛的资源可用性和植物物种特征的后果。最后，强调系统级响应的机制，通过关联模型整合，应该使本研究的结果推广到其他生态系统。

Drs. Field, Chapin and Mooney will conduct integrated studies of the responses of California annual grassland to altered resource balance, focusing on factors controlling the response of the ecosystem to elevated CO2. Their research involves coordinated empirical and modeling programs to test a series of hypotheses that potentially account for the mechanisms and feedbacks governing system-level behavior of aboveground and belowground production, decomposition, and nutrient cycling in response to altered resources. The conceptual model for the system-level effects of elevated CO2 is based on two hypotheses concerning the mechanisms of the system level responses and the loci of the direct effects. First, they hypothesize that elevated CO2 may generate novel resource balance, but the response of plant growth can be understood and predicted from responses of other variations in resource balance that change the availability of carbon, relative to other resources. Second, they hypothesize that system-level responses to elevated CO2 are driven primarily through direct effects on plants. This research program consists of five components: 1) a study of the responses of natural ecosystems to elevated CO2 in open top chambers. 2) a probe of ecosystem responses to a range of modifications, including elevated CO2, altered nutrient and water availability, and altered species composition, using artificial microecosystems in open top chambers. 3) a study of controls on decomposition and nutrient cycling with laboratory, field and microecosystem experiments using plant litter from the other experiments as well as isotopic tracers. 4) an exploration of the resource effects on plant growth, allocation, and tissue chemistry with a series of greenhouse experiments. 5) a modeling effort to integrate the experimental results and to link and extend existing ecosystem, community, and plant models. This program has the potential to advance several aspects of our understanding of system-level responses to global climate change. First, studies with elevated CO2 in the California annual grassland will complement CO2 studies in other grasslands, with results from a system that is unique in terms of low carbon storage and rapid equilibration. Second, the small stature of the plants, combined with the small time constant for system equilibration, will allow the investigators to explore consequences of a broad range of resource availabilities and plant species characteristics. Finally, the emphasis on mechanisms of system-level responses, integrated through linked models, should make the results of this study generalizable to other ecosystems.