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

人类活动使陆地上可用的氮量增加了一倍多，主要是通过生产肥料和燃烧化石燃料。虽然氮常常限制植物生长，但过多的氮会在许多方面对生态系统产生有害影响，包括造成生物多样性的损失，以及导致水质问题。令人惊讶的是，这些影响在落基山脉高山冻土带被观察到，即使在相对较低的大气氮沉积水平。因此，随着氮输入的增加，高山冻土带抵抗显著变化的能力可能相当低。虽然从冻土带输入和输出的氮是相当众所周知的，但对氮保留和损失的控制却没有得到很好的解决。特别是，我们需要更多关于土壤中所含大型有机质库的潜在作用的信息。我们将在高寒冻土带的一系列长期氮肥地块上应用稳定的氮同位素标签。然后，我们将在接下来的几个月和几年里追踪这个标签的命运；这些信息将显示高山冻土带生态系统中多余的氮是如何以及在何处储存和/或损失的。这些发现将增强我们对高价值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.