Cycling of NO3-N in Northern Hardwood Forests: Regulation and Consequences of N Saturation

北方阔叶林NO3-N的预先循环：N饱和的调控和后果将在密歇根州糖枫林中进行一系列实验，以确定慢性大气硝酸盐（NO3-）沉积的潜在后果。该实验将利用一种示踪剂，即稳定的同位素15N，来进行研究，以确定添加的NO3-的即时和长期命运。这些试验将监测对森林健康和生产力至关重要的过程，这些研究地块接收的NO3—N输入量是正常大气NO3—N输入量的四倍。研究人员将跟踪添加的NO3-的内部生态系统循环，从而评估密歇根糖枫林对大气氮输入的N饱和的敏感性。假设长期添加NO3-将逐渐增加氮素有效性，改变地上和地下森林生产力。当森林吸收添加的NO3-的能力最终超过时，就会发生氮饱和，导致NO3-和其他营养物质（如钙和镁）的大量淋失，可能导致营养失衡和生产力下降。这项密歇根糖枫森林研究将检验这些假设，并为生态系统调节氮饱和度的内部机制提供更基本的理解。

9629842 Pregitzer Cycling of NO3-N in Northern Hardwood Forests: Regulation and Consequences of N Saturation A series of experiments will be conducted in Michigan sugar maple forests to determine the potential consequences of chronic atmospheric nitrate (NO3-) deposition. The experiments will utilize a tracer, the stable isotope 15N, to do studies to determine the immediate and long-term fates of added NO3-. The experiments will monitor processes important to forest health and productivity on study plots that receive four times the amount of normal atmospheric NO3--N inputs. The researchers will follow internal ecosystem cycling of the added NO3-, enabling the assessment of the susceptibility of Michigan sugar maple forests to N saturation from atmospheric nitrogen inputs. It is hypothesized that long-term NO3- additions will gradually increase N availability, altering above- and below-ground forest productivity. When the forest's capacity to assimilate added NO3- is finally exceeded, N saturation should occur, resulting in large leaching losses of NO3- and other nutrients such as calcium and magnesium, potentially leading to nutrient imbalances and decreased productivity. This Michigan sugar maple forest study will test these hypotheses and provide a more fundamental understanding of the internal mechanisms through which ecosystems regulate N saturation.