DISSERTATION RESEARCH: Nitrogen Deposition and Population Dynamics of a Declining Nitrogen-fixing Plant Species

大气氮沉降可能对全球生物多样性产生重大影响，特别是在温带森林。豆类和其他固定大气氮的植物可能对氮沉积的增加特别敏感，但这种敏感性在种群下降中的可能作用尚未被调查。在过去的30-40年里，随着美国东北部氮素沉降量的增加，新英格兰多年生豆科植物--虎杖(大苞片三叶草)的种群数量有所下降。这些种群数量的减少与栖息地的丧失、转换或碎片化无关。结合广泛的地理取样、温室实验和人口模型，将确定是否可以至少部分地通过氮沉积对个体生长、繁殖和生存的影响来解释虎杖的衰落。范围广泛的遗传分析将调查遗传多样性的模式是否符合最近人口下降的预期。由于可用于保护的资源有限，使一系列相似物种受益的努力比只关注一个物种的努力更可取。虎杖是新英格兰110种需要研究的珍稀植物之一，是豆科植物科(Fabaceae)的成员，占《国家濒危植物名录》物种的10%。此外，这种植物家族中36%的成员在美国被认为处于危险之中。这项研究的结果将有助于确定保护重点，指导虎杖的管理，并将影响其他稀有豆科植物的保护策略。

Atmospheric nitrogen deposition is likely to have globally significant effects on biodiversity, particularly in temperate zone forests. Legumes, and other plants that fix atmospheric nitrogen, may be particularly sensitive to increases in nitrogen deposition but the possible role of this sensitivity in population declines has not been investigated. In the last 30-40 years, New England populations of the perennial legume, Desmodium cuspidatum (large-bracted tick-trefoil), have declined as nitrogen deposition in the northeastern US has increased. These population declines are not associated with habitat loss, conversion or fragmentation. A combination of wide geographical sampling, greenhouse experiments and demographic modeling will be used to determine whether the decline of D. cuspidatum can be explained, at least in part, by the effects of nitrogen deposition on individual growth, reproduction, and survivorship. Range-wide genetic analyses will investigate whether patterns of genetic diversity correspond with those expected from recent population declines. Because resources available for conservation are limited, efforts that benefit a suite of similar species are preferable to those that focus on only one. Desmodium cuspidatum is among 110 rare plant species in need of research in New England and is a member of the plant family (Fabaceae) that accounts for 10% of the species in the National Collection of Endangered Plants. Furthermore, 36% of the members of this plant family are considered at risk in the US. The results of this study will help determine conservation priorities, will guide management for D. cuspidatum, and will influence conservation strategies for other rare legumes.