Dissertation Research: Constraints on Invasion by a Nitrogen-fixing Woody Shrub and Consequences for Resident Grassland Species

灌木(尤其是固氮灌木)对草原的入侵已经引起了人们的广泛关注，但我们还不清楚固氮在入侵过程中所起的作用。特别是，我们不知道土传互助者对固氮效率施加了什么限制，也不知道居民群落的养分限制在多大程度上有助于固氮的竞争优势。这项研究将调查三个问题，以解决限制固氮灌木入侵加州沿海草原栖息地的能力，以及这种固定对栖息地物种相互作用的影响：(1)扫帚进入草原栖息地的成功定植如何随着栖息地物种的营养限制而变化？(2)无毒根瘤菌的可用性或质量如何影响该物种入侵和固定氮素的能力？(3)土壤固氮的肥沃如何影响物种之间的相互作用？加州沿海草原提供了进行这项研究的理想机会，因为它们缺乏重要的本地固氮成分，本身就是氮素有限的，目前正经历着几种引入的固氮灌木的戏剧性入侵。

0073068D'AntonioInvasions by wood shrubs (particularly those that fix nitrogen) into grasslands have received much attention, yet we do not understand the role that N-fixation plays in the invasion process. In particular, we do not know what constraints may be imposed by soil-borne mutualists on fixation efficiency, nor the degree to which nutrient limitation of the resident community contributes to the competitive advantage of N-fixation. This research will investigate three questions that address constraints on a nitrogen-fixing shrub's ability to invade a coastal California grassland habitat, and the consequences of that fixation for resident species interactions: (1) How does the success of colonization by broom into grassland habitat change with nutrient limitation of the resident species? (2) How does availability or quality of Rhizobium innoculum affect this species" ability to invade and fix nitrogen? (3) How does enrichment of soil by N-fixation affect species interactions? Coastal California grasslands offer an ideal opportunity to perform this research because they lack a significant native N-fixing component, are themselves nitrogen limited, and are currently experiencing dramatic invasions by several introduced N-fixing shrubs.