Dissertation Research: Responses and Feedbacks of Biological N Fixation to Elevated Atmospheric CO2 and Ecosystem N Availability

9801217 Vitousek关于陆地生物圈与大气二氧化碳（CO2）水平上升之间的反馈的经验和理论工作表明，许多生态系统增加碳（C）吸收和储存的能力受到有限资源（特别是氮（N））可获得性的强烈影响。生物固氮是许多陆地系统的主要氮源，并对环境条件的变化作出反应。因此，氮固定器的响应CO2浓度升高可能会影响生态系统的反应，通过氮的可用性的变化。 将在加州一年生草地生态系统中进行两个实验。第一个将测量CO2浓度升高下的生长和固氮的时间和幅度，以确定生长反应是否可以等同于生物N输入的变化。生物量，分配，和固氮活性的3豆科植物生长在环境和高浓度CO2将在整个生长季节的过程中进行测量。实验2将测试CO2浓度升高对氮固定和非固定植物的影响，这些植物沿着氮有效性的梯度一起和分开生长。主要的测量包括生物量和分配的反应，来自N固定的植物N的贡献，以及固定器和非固定器的组织化学的变化。

9801217 Vitousek Empirical and theoretical work on the feedbacks between the terrestrial biosphere and rising levels of atmospheric carbon dioxide (CO2) has demonstrated that the capacity of many ecosystems to increase carbon (C) uptake and storage is strongly influenced by the availability of limiting resources, particularly nitrogen (N). Biological N-fixation is a major source of N to many terrestrial systems and is responsive to changes in environmental conditions. As a result, the response of N fixers to elevated CO2 is likely to affect ecosystem responses through changes in N-availability. Two experiments will be carried out in a California annual grassland ecosystem. The first will measure the timing and magnitude of growth and N-fixation under elevated CO2 to determine whether growth responses can be equated with changes in biological N-inputs. Biomass, allocation, and N-fixing activity of 3 legumes grown under ambient and elevated CO2 will be measured over the course of the growing season. Experiment 2 will test the effects of elevated CO2 on N-fixing and non-fixing plants grown together and separately along a gradient of N-availability. Primary measurements include biomass and allocation responses, the contribution of plant N derived from N-fixation, and changes in tissue chemistry of fixers and non-fixers.