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

人类活动主要是通过化肥生产和燃烧化石燃料，使陆地上的有效氮量增加了一倍以上。尽管氮往往会限制植物的生长，但过多的氮会在许多方面对生态系统造成有害影响，包括导致生物多样性的丧失，以及导致水质问题。令人惊讶的是，即使在大气氮沉积相对较低的情况下，这些影响也在落基山高山冻原上观察到了。因此，高山冻土带抵御氮素输入增加后的显著变化的能力可能相当低。尽管来自冻土带的氮的输入和输出是众所周知的，但对氮的保留和损失的控制解决得很差。特别是，我们需要更多关于土壤中包含的大型有机物质池的潜在作用的信息。我们将在高山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，我们将在随后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哪里储存和/或丢失的。这些发现将加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.