COLLABORATIVE RESEARCH: Responses of Productivity and Nutrient Dynamics to Elevated CO2 in an Intact Mojave Desert Ecosystem.

内华达沙漠FACE设施（NDFF）是一个长期研究项目，旨在研究完整的莫哈韦沙漠生态系统对二氧化碳升高的反应。在NDFF运行的前4年，我们发现初级产量在CO2升高的情况下显著增加，但仅在湿润年，并且外来一年生草的响应比本地灌木和一年生草更强烈。因此，我们的初步结果表明，占地球陆地面积30%的生态系统类型（旱地）可能不会像现有的全球变化模型所预测的那样，以一种简单的方式对二氧化碳的升高做出反应。在这些结果的背景下，以及我们的沙漠FACE实验的长期性，我们建议在本研究中解决三个首要问题：二氧化碳浓度升高是否会继续刺激外来一年生物种不成比例的增加，从而改变莫哈韦沙漠的群落组成和结构？我们所观察到的因二氧化碳的阶梯式增加而引起的产量的增加和营养动态的变化是否会随着时间的推移而持续？我们能否利用已证实的沙漠生态系统功能模型来预测莫哈韦沙漠生态系统对未来二氧化碳浓度升高的反应？这一建议的智力价值在于我们的概念方法，我们专注于物种组成和生态系统功能之间的功能相互作用，通过一个明确的建模组件联系在一起。该模型将是对已建立的、经过验证的沙漠模型（PALS, Patch Arid Lands Simulator）的改编，该模型将用于对干旱生态系统中碳、氮和水通量对二氧化碳升高的生物和非生物控制进行综合理解。这项研究的更广泛的影响将是研究外来物种对二氧化碳升高的潜在入侵，以及这一过程如何影响沙漠环境中的生态系统功能，从而影响生态系统服务。通过这个研究项目，我们还在五个研究校区之间建立了一个有凝聚力的网络。迄今为止，我们的研究小组在培养NDFF的本科生、研究生和博士后学者方面有着出色的记录，包括代表性不足的群体的成员。这项研究同样将在NDFF和我们的支持实验室培养广泛的学生和博士后。

The Nevada Desert FACE Facility (NDFF) is a long-term research project examining the responses of an intact Mojave Desert ecosystem to elevated CO2. In the first four years of NDFF operation, we found that primary production increased substantially at elevated CO2, but only in wet years, and that an exotic annual grass responded more strongly than did native shrubs and annuals. Therefore, our initial results suggest that an ecosystem type (drylands) that represents 30% of the earth's terrestrial surface area may not respond to elevated CO2 in a simple manner, as predicted by existing models of global change.In the context of these results and the long-term nature of our desert FACE experiment, we propose to address three overarching questions in this study:1. Will elevated CO2 alter community composition and structure in the Mojave Desert by continuing to stimulate a disproportionate increase in an exotic annual species?2. Will the increases in production and changes in nutrient dynamics that we have observed in response to a step-change increase in CO2 be sustained over time?3. Can we adapt proven models of desert ecosystem function to predict how this Mojave Desert ecosystem will respond to elevated CO2 in the future?The intellectual merit of this proposal lies in our conceptual approach in which we are focusing on the functional interactions between species composition and ecosystem function, tied together by an explicit modeling component. The model will be an adaptation of an established, validated desert model (PALS, the Patch Arid Lands Simulator) that will be used to develop a synthetic understanding of biotic and abiotic controls on carbon, nitrogen, and water fluxes to elevated CO2 in this arid ecosystem. The broader impact of this proposed study will be an examination of the potential invasion of an exotic species in response to elevated CO2, and how this process may impact ecosystem function, and therefore ecosystem services, in a desert environment. Through this research program, we are also forging a cohesive network between five research campuses. To date, our research group has an excellent record of training undergraduate, graduate, and postdoctoral scholars at the NDFF, including members of underrepresented groups. This study will similarly train a wide spectrum of students and postdocs, both at the NDFF and in our support laboratories.