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。豆科植物和其他固定大气氮的植物可能对氮沉降的增加特别敏感，但这种敏感性在种群减少中的可能作用尚未得到调查。在过去的30-40年里，随着美国东北部氮沉降的增加，新英格兰地区多年生豆科植物虎斑蝶（大苞叶蜱三叶草）的种群数量有所下降。这些种群的减少与栖息地的丧失、转换或破碎化无关。广泛的地理采样、温室实验和人口统计学模型相结合，将用于确定虎杖的下降是否可以解释，至少部分，氮沉降对个体生长、繁殖和生存的影响。范围广泛的遗传分析将调查遗传多样性的模式是否与最近人口下降的预期相一致。由于可用于保护的资源是有限的，因此对一组相似物种有利的努力比只关注一种物种更可取。虎棘菊是新英格兰110种需要研究的稀有植物之一，是占美国国家濒危植物收藏物种10%的豆科植物的一员。此外，该植物家族中36%的成员在美国被认为处于危险之中。本研究结果将有助于确定虎杖草的保护重点，指导虎杖草的管理，并对其他珍稀豆科植物的保护策略产生影响。

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.