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

灌木入侵草原导致植物群落结构的长期变化，这表明美国西南部的荒漠化。灌木替代草地也可能影响生态系统养分循环的动态。荒漠灌木的寿命和“肥沃之岛”荒漠灌丛下土壤养分的长期积累可能对持续荒漠化起到积极的生物反馈作用。这项研究将最新的稳定同位素技术与传统的土壤科学和植物生态学方法相结合，以解决以下问题：1)哪些土壤养分构成肥力岛？2)随着荒漠化的进行，生物调节的土壤养分是否在空间上变得更加不均匀？3)灌木的存在或不存在如何影响肥力岛的形成和退化的速度？4)土壤养分浓度是否与肥力岛的发育程度有关，新墨西哥州塞维莱塔西北地区的C3灌丛最近是否取代了C4草地？这项研究的答案将为更全面地了解美国西南部的荒漠化动态提供宝贵的见解。

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.