Effects of Elevated CO2 on a Mojave Desert Ecosystem

9524144目前大气中的二氧化碳水平比工业化前的水平高出25%以上。 根据目前碳进入大气层的速度所作的预测表明，在不到一个世纪的时间里，大气层中的二氧化碳含量将增加一倍。 尽管人们对这一增加是否会导致严重的全球变暖存在争议，但毫无疑问，这一增加将对植物产量产生潜在的巨大影响，并可能导致世界主要生态系统的植物组成发生变化。 有必要了解由于大气中温室气体浓度上升，特别是二氧化碳浓度上升，世界主要生态系统类型将出现的各种反应，而且这些实验必须在完整的生态系统中进行，而不是在温室或生长室等人工条件下。 沙漠占地球陆地面积的最大百分比 区域， 和 通过工艺 的 全球荒漠化地区的地表面积增长最快。 荒漠化也是预计对全球变化最敏感的生态系统类型，因为二氧化碳的升高缓解了植物水分胁迫的影响。 二氧化碳浓度升高可能会严重影响 的生产力和生物多样性 的 荒漠生态系统的变化，并导致这一普遍生态系统类型的功能和土地使用模式发生重大变化。 然而，还没有任何大规模的研究， 全球变化的影响， 沙漠生态系统 莫哈韦沙漠是北美最干旱的沙漠之一，与世界其他地区的真正沙漠最相似，因此有可能作为研究沙漠植被对二氧化碳浓度升高的反应的模型系统。 A自由空气二氧化碳 浓缩（FACE）系统目前 正在内华达州南部莫哈韦沙漠内的内华达州试验场建造。 这项技术需要一系列实验性的“环”，其中不断向每个环内的完整生态系统提供升高的二氧化碳，并且不会改变气候。 的 网站 人工围栏。 本研究将进行的具体实验包括分析植物生产、繁殖和生存以及景观水平衡对二氧化碳浓度升高的响应。 这些具体的实验将通过一个 系列 将专门为莫哈韦沙漠开发的基于生态系统的模型。 模拟工作将特别强调两个综合概念：（1）在极端干燥和贫瘠的沙漠土壤下，植物之间的激烈竞争控制着生态系统的功能，而二氧化碳浓度升高可能会改变竞争性 目前存在的余额; 和 (2)招聘 和植物的生存 沙漠 由偶发性条件（干旱和异常湿润循环）决定，二氧化碳浓度升高可能会改变植物对这些偶发性条件的反应。 沙漠生态系统可能 在二氧化碳浓度升高的情况下，生态系统的生产力会更高，用水效率也会更高，但复杂的生态系统反馈过程可能会长期限制这一反应。 像这样的实验将提供我们需要的数据来预测这些变化将如何影响干旱的土地。

9524144 Current atmospheric carbon dioxide levels are more than 25% higher than pre-industrial levels. Projections based upon the present rate of carbon input into the atmosphere indicates that the atmospheric carbon dioxide content will double in less than a century. Although there is debate as to whether this increase will result in significant global warming, there is little doubt that this increase will have potentially dramatic effects on plant production and will possibly result in changes in plant composition of major world ecosystems. There is a need to understand the spectrum of responses that will occur over the major ecosystem types of the world as a consequence of rising atmospheric greenhouse gas concentrations, most notably carbon dioxide, and it is critical that these experiments be conducted in intact ecosystems, not in artificial conditions such as greenhouses or growth chambers. Deserts account for the largest percentage of the earth's land surface area, and through the process of global desertification, are showing the most rapid increase in surface area. Deserts are also the ecosystem type that are predicted to be the most sensitive to global change because elevated carbon dioxide relaxes the effects of water stress in plants. Elevated carbon dioxide may significantly impact the productivity and biodiversity of desert ecosystems and result in a substantial change in the function and land-use patterns of this prevalent ecosystem type. However, there have yet to be any large-scale studies of the effects of global change on desert ecosystems. The Mojave Desert is one of the most arid deserts in North America and most resembles true deserts in other parts of the world, giving the potential to serve as a model system for the study of the response of desert vegetation to elevated carbon dioxide. A Free Air carbon dioxide Enrichment (FACE) system is currently being constructed on the Nevada Test Site within the Mojave Desert of southern Nevada. This technology entails a series of experimental "rings" in which elevated carbon dioxide is constantly supplied to an intact ecosystem within each ring, and does not otherwise alter the climate of the site with artificial enclosures. Specific experiments to be conducted in this study include analysis of the responses of plant production, reproduction and survival, and landscape water balance to elevated carbon dioxide. These specific experiments will be integrated through a series of ecosystembased models that will be developed specifically for the Mojave Desert site. The modeling effort will particularly emphasize two integrating concepts: (1) under the extremely dry and infertile soils of deserts, intense competition between plants controls the function of the ecosystem, and elevated carbon dioxide may change the competitive balance that currently exists; and (2) recruitment and survival of plants in deserts are determined by episodic conditions (droughts and abnormal wet cycles), and elevated carbon dioxide may change plant responses to these episodic conditions. Desert ecosystems may become more productive and will use water more efficiently under elevated carbon dioxide, but complex ecosystem feedback processes may limit this response over the long term. Experiments like this will provide the data we need to predict how these changes will affect arid lands.