DISSERTATION RESEARCH: Soil Organic Matter Controls Over Nitrogen Retention in Alpine Tundra

人类活动使土地上的可用氮量增加了一倍多，这主要是通过化肥生产和化石燃料的燃烧。尽管氮通常会限制植物生长，但过多的氮会以多种方式对生态系统产生有害影响，包括导致生物多样性丧失以及导致水质问题。令人惊讶的是，即使在大气氮沉降水平相对较低的情况下，在落基山高山苔原上也观察到了这些效应。因此，高山苔原抵抗氮输入增加后发生显着变化的能力可能相当低。虽然苔原氮的输入和输出众所周知，但对氮保留和损失的控制却很难解决。 特别是，我们需要更多关于土壤中大型有机物库的潜在作用的信息。我们将在高山苔原的一系列长期施氮肥地块上应用稳定氮同位素标签。 然后，我们将追踪这个标签在接下来的几个月和几年里的命运；此类信息将显示高山苔原生态系统中过量氮的储存和/或流失方式和地点。 这些发现将增强我们对高度重视的生态系统如何应对人类驱动的重大环境变化的理解，从而有可能为国家和区域环境政策提供信息。

Human activity has more than doubled the amount of available nitrogen on land, primarily through fertilizer production and the burning of fossil fuels. Though nitrogen often limits plant growth, too much nitrogen can deleteriously affect ecosystems in many ways, including causing losses in biodiversity, as well as leading to water quality problems. Surprisingly, these effects have been observed in Rocky Mountain alpine tundra, even at relatively low levels of atmospheric nitrogen deposition. Thus, alpine tundra may have a fairly low capacity to resist significant changes following increasing nitrogen inputs. While inputs and exports of nitrogen from the tundra are fairly well known, the controls over nitrogen retention and loss are poorly resolved. In particular, we need much more information on the potential role of the large organic matter pools contained in soils. We will apply a stable nitrogen isotope label to a range of chronic nitrogen fertilizer plots in alpine tundra. We will then trace the fate of this label over subsequent months and years; such information will show how and where excess nitrogen is stored and/or lost in alpine tundra ecosystems. These findings will enhance our understanding of how a highly valued ecosystem may respond to a major human-driven environmental change, and thus have the potential to inform national and regional environmental policy.