Collaborative Research: Sensitivity of Ecosystem Processes to Precipitation Across a Grassland to Shrubland Vegetation Transition in the Southwestern U.S.

该项目提出了一个普遍的问题，即由不同类型的植物组成的生态系统如何使用水和处理二氧化碳。 具体而言，该项目将评估在半干旱，美国西南部的草原与灌木林生态系统中的水利用和碳处理的差异。在该地区，植被的水利用可以影响水流行为和随后人类奋进的水的可用性。 此外，该地区的植被如何处理大气中的碳可能会影响北美的碳汇与碳源特征。 该项目将在河岸和高地的五个地点评价水的使用和碳的处理，每个地点都将评价不同植被类型（在以草为主和以灌木为主之间）。 该项目将测量整个生态系统的光合作用行为，沿着通过大规模气象技术评估的植被用水模式。 降雨模拟将在草地和灌木丛中进行，以了解降雨事件的变化如何影响这些生态系统的功能。这项工作的动机是下世纪北美生物群落内植被组成的预期变化。 这种植被变化可以说是全球变化最普遍和最重要的表现。 目前北美草原和热带稀树草原生态系统中木本植物密度的增加可能是北美碳汇的一个重要贡献者。 植被组成的这种变化如何影响景观水收支尚不清楚，但可能直接影响地球仪水资源有限地区的社会。 最重要的问题是北美降雨时间和强度的预期变化。 这些问题共同表明，需要更好地了解植被类型、用水、碳处理和气候变化（主要是降雨量）之间的相互联系。 该项目将大大有助于国家科学基金会在产生跨学科知识和教育学生方面的目标。 该计划代表了具有不同背景和专业领域的几位研究人员之间的合作，因此将促进跨植物生理生态学，生态系统生态学和水文学的新的跨学科方法。 研究生，包括女性和代表性不足的群体，将参与所提出的科学的各个方面。 从事该项目的研究生将通过K-12教学/研究奖学金向其他人传播该项目的信息和热情。 该项目的研究目标和个人成员是国家科学基金会科学和技术中心“半干旱水文和河岸地区的可持续性”（SAHRA-http：//www.example.com）长期重点的关键组成部分。www.sahra.arizona.edu该项目将促进上圣佩德罗伙伴关系的目标，该伙伴关系是一个由20个机构和组织组成的联合体，致力于满足该地区居民的用水需求，同时保护圣佩德罗河（http：www.usppartnership.com）。在这个项目中雇用的本科生将从亚利桑那大学的一个项目（本科生物学研究项目）中招募，该项目积极鼓励为代表性不足的群体提供研究机会。

This project asks the general question of how ecosystems composed of different types of plants use water and process carbon dioxide. Specifically, this project will evaluate the differences in water-use and carbon processing in grassland versus shrubland ecosystems of the semi-arid, southwestern U.S. In this region, water-use by vegetation can influence stream behavior and the subsequent availability of water for human endeavor. Additionally, how vegetation in this region processes carbon from the atmosphere may influence the carbon sink-versus-source characteristics of North America. This project will evaluate water-use and carbon processing at five sites in both riparian and upland settings each with a gradient of vegetation types (between grass-dominated and shrub-dominated) will be evaluated. The project will measure the photosynthetic behavior of whole ecosystems, along with patterns of vegetation water-use as assessed via large-scale meteorological techniques. Rainfall simulations will be employed in grasslands and shrublands to understand how a change in rainfall events affects the way these ecosystems function.This work is motivated by the expected shift in vegetation composition within North America's biomes in the next century. This vegetation change is arguably the most ubiquitous and significant manifestation of global change. The current increase in the density of woody plants in North America's grassland and savanna ecosystems may be an important contributor to the North American carbon sink. How such a change in vegetation composition affects landscape water budgets is unknown, yet may directly influence society in water-limited regions of the globe. On top of these issues are the expected shifts in the timing and magnitude of rainfall in North America. Together these issues suggest the need for a greater understanding of how vegetation type, water-use, carbon processing and variation in climate (primarily rainfall) are interlinked. This project will contribute substantially to the goals of the National Science Foundation in the production of interdisciplinary knowledge and education of students. This program represents a collaboration among several researchers with distinct backgrounds and areas of expertise and hence will foster novel interdisciplinary approaches cutting across plant physiological ecology, ecosystem ecology and hydrology. Graduate students, including females and underrepresented groups, will be involved in all aspects of the science proposed. Graduate students working on this project will disseminate the information and enthusiasm derived from this project to others through K-12 Teaching / Research Fellowships. The research goals and individual members of this project are critical components of the long term focus of the NSF Science and Technology Center "Sustainability of semi-Arid Hydrology and Riparian Areas" (SAHRA-http://www.sahra.arizona.edu). This project will further the goals of the Upper San Pedro Partnership, a consortium of 20 agencies and organizations working to meet the water needs of area residents while protecting the San Pedro River (http://www.usppartnership.com). Undergraduate students employed in this project will be recruited from a program at the University of Arizona (Undergraduate Biology Research Program) that actively encourages research opportunities for under-represented groups.