Dissertation Research: Biogeochemistry at the Desert Shrubland-Desert Grassland Boundary

灌木入侵草原导致植物长期变化 表明荒漠化的群落结构 美国西南部。 灌木取代草地可能 也影响生态系统养分循环的动态。 两 荒漠灌木的长寿和长期积累的 “肥沃之岛”沙漠灌木下的土壤养分可能 作为一个积极的生物反馈， 荒漠化 这项研究结合了最先进的稳定同位素技术， 传统的土壤科学和植物生态学方法来解决 以下问题：1）哪些土壤养分构成了一个岛屿， 生育能力？2)生物调节的土壤养分是否变得 随着荒漠化的发展，空间上的异质性如何？第三章 灌木的存在或不存在如何影响岛屿的比率？ 生育力的形成和退化？（4）土壤养分 浓度与肥力岛的程度有关 发展和C3灌木林最近取代C4草地， 新墨西哥州的塞维利亚西北铁路 这项研究的答案将提供有价值的见解， 更全面地了解荒漠化的动态 在美国西南部。

Shrub invasions into grassland cause long term changes in plant community structure that are indicative of desertification in the southwestern United States. Shrub replacement of grassland may also influence the dynamics of ecosystem nutrient cycling. Both the longevity of desert shrubs and the long term accumulation of soil nutrients under desert shrubs in "islands of fertility" may act in tandem as a positive biological feedback for continued desertification. This study combines state-of-the-art stable isotope techniques with traditional soil science and plant ecology methods to address the following questions: 1) Which soil nutrients comprise an island of fertility?; 2) Do biotically-regulated soil nutrients become more spatially heterogeneous over time as desertification proceeds?; 3) How does shrub presence or absence affect rates of island of fertility formation and degradation?; and 4) Does soil nutrient concentration correlate to the degree of island of fertility development and has C3 shrubland recently replaced C4 grassland at the Sevilleta NWR, New Mexico? Answers from this research will provide valuable insight towards a more complete understanding of the dynamics of desertification in the southwestern United States.