Precipitation Controls of Carbon and Nitrogen Cycles in Arid-Semiarid Ecosystems

该奖项是根据《2009年美国复苏和再投资法案》(公共法律111-5)资助的。尽管降水被认为是干旱和半干旱地区植物生产的主要控制因素，但年降雨量只解释了草和灌木产量年间变化的20%-40%。这一失败表明，研究人员没有考虑到控制干旱生态系统跟踪降水波动能力的关键机制。然而，波动加剧是干旱地区气候预测的一个显著特征。该项目提出了四个假设来解释观测到的生态系统对降水变化的滞后反应，并通过改变总降水量和降水量变异性的模式，在有无氮素调控的情况下对它们进行了检验。这些操作，加上模型分析，将有助于确定生态系统对降水反应滞后的原因和程度。该项目的结果将有助于了解气候变化对碳汇、牧草生产和灌木入侵过程的影响，这些对美国西南部的利益相关者非常重要，从养牛场到担心供水和生态系统服务的市政当局。将与一个非营利性组织合作建立一个示范项目，该组织每年为新墨西哥州南部和得克萨斯州西部的12000多名儿童和4500多名成年人提供获奖的科学教育。此外，该项目还将开发网站和宣传材料，将调查结果传播到大学以外的地方。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Although precipitation is assumed to be the major control of the production of plants in arid and semiarid regions, annual precipitation explains only 20-40% of grass and shrub production variability among years. This failure suggests that researchers are not accounting for key mechanisms that control the ability of arid ecosystems to track fluctuations in precipitation. Yet increased fluctuations are a prominent feature of climate predictions in arid regions. This project puts forward four hypotheses to explain observed lags in ecosystem response to changing precipitation, and tests them by altering patterns of total precipitation and precipitation variability, with and without nitrogen manipulation. These manipulations, together with the model analysis, will help determine the cause and magnitude of lags in the ecosystem response to precipitation. Results from this project will contribute to understanding the effect of climate change on carbon sequestration, forage production and the process of shrub encroachment, which are very important for stakeholders of the southwestern U.S., ranging from cattle ranchers to city authorities worrying about water supplies and ecosystem services. A demonstration project will be established in partnership with a nonprofit organization that provides award-winning science education to more than 12,000 children and 4,500 adults annually in southern New Mexico and western Texas. In addition, the project will develop web sites and outreach materials to transmit findings beyond the university.