Shortgrass Steppe Ecosystem Dynamics and Trace Gas Exchange Under Elevated CO2

9524068未来大气中的二氧化碳浓度几乎肯定会至少是目前浓度的两倍。至关重要的是，研究解决这种戏剧性的变化将如何影响生态系统，特别是那些粮食生产所需的生态系统。大平原广袤的半干旱草原几千年来一直被广泛放牧，由具有正常(C3)和节水(C4)光合作用途径的草种组成。目前尚不清楚大气中二氧化碳浓度升高将如何影响美国西部的短草草原生态系统。二氧化碳浓度的增加可能会通过提高单个植物的碳、氮和水的利用效率来影响干旱和半干旱生态系统的生产力，并可能因为C3和C4植物的不同反应而影响它们之间的竞争平衡。生长模式、养分利用和物种组成的改变可能会改变土壤的氮和碳循环，并影响草原的长期生存能力。这项研究将使用大型开顶式气室进行田间二氧化碳浓缩，并通过土壤氮素循环和微量气体通量测量来研究植物生理和土壤养分平衡。本研究有三个基本目标。首先，它将确定二氧化碳加倍对C3和C4两种优势草种的光合作用、生产力、水分和氮素利用效率、植物水分关系以及地上和地下碳和氮分配的影响。其次，它将确定二氧化碳倍增对土壤水氮动态的影响。从这些研究中获得的知识将被整合到模拟模型中，从而能够通过土壤水分、养分循环、植物生产力和整体生态系统响应的时间和空间进行现实的外推。该计划将深入了解二氧化碳升高对该生态系统的影响，以帮助维持短草草原的长期生存能力。

9524068 Future atmospheric carbon dioxide concentrations will almost certainly be at least twice as high as current concentrations. It is crucial that research address how such a dramatic change will affect ecosystems, especially those needed for food production. The vast semiarid grasslands of the Great Plains has been grazed extensively for thousands of years, and is comprised of grass species that have "normal" (C3) and water-efficient (C4) photosynthetic pathways. It is not known how elevated atmospheric carbon dioxide concentration will affect the shortgrass steppe ecosystem of the western United States. Increasing carbon dioxide concentrations will likely impact the productivity of arid and semiarid ecosystems through increased carbon, nitrogen and water use efficiencies in individual plants and may affect the competitive balance between C3 and C4 plants because of their different responses. Changing patterns of growth, nutrient use, and species composition may alter soil nitrogen and carbon cycles and affect the long term viability of the grassland. This research couples the use of large, open-top chambers for field carbon dioxide enrichment with studies of plant physiology and soil nutrient balance through soil nitrogen cycling and trace gas flux measurements. There are three basic objectives in this research. First, it will determine the impact of doubling carbon dioxide on photosynthesis, productivity, water and nitrogen use efficiency, plant water relations, and allocation of carbon and nitrogen above- and below-ground in two dominant grass species, one a C3 grass and the other a C4 grass. Second, it will determine the impact of doubling carbon dioxide on soil water and nitrogen dynamics. The knowledge gained from these studies will be incorporated into simulation models that will allow for realistic extrapolation through tim e and space of soil moisture, nutrient cycling, plant productivity, and overall ecosystem response. This program will provide insight into the effect of elevated carbon dioxide on this ecosystem to help maintain long term viability of the shortgrass steppe.