COLLABORATIVE RESEARCH: Nitrogen Retention and Ecosystem Succession: Theory Meets Data

氮是森林的关键营养物质，而氮的缺乏往往会限制森林的生长。生态学的理论考虑表明，随着森林年龄的增长和生长速度的放缓，它从土壤中吸收氮素的速度也应该会放缓，从而导致排水中氮素的损失增加。对新汉普郡哈伯德布鲁克实验森林中氮素的长期测量结果与预期的模式相矛盾。该项目试图通过测试以下假设来理解理论和数据之间的差异：幼林从深层土壤中提取氮素，但随着森林年龄的增长，土壤中氮素的重新积累会延缓排水中氮素的损失。这一假说将通过实地实验来验证，以确定不同树龄的林木下土壤中氮素的积累倾向，并仔细计算从15年到200年以上的森林序列中的氮素含量。此外，还将修订森林生态系统的计算机模拟模型，以纳入这些新的观测结果。这项工作对森林管理非常重要，以尽量减少氮的损失，氮是一种关键的植物养分。空气污染给森林增加了过量的氮，如果它消失在排水中，就会污染溪流和湖泊。该项目将培训两名研究生和两名博士后助理，教师培训模块将帮助两名高中科学教师开发一个在课堂上教授森林生态的单元。

Nitrogen is a critical nutrient for forests, and scarcity of nitrogen often limits forest growth. Theoretical considerations in ecology indicate that as a forest ages and its growth slows, its uptake of nitrogen from the soil should also slow, leading to increased loss of nitrogen in drainage water. Long-term measurements of nitrogen in streams draining the Hubbard Brook Experimental Forest in New Hampshire contradict this expected pattern. This project seeks to understand the discrepancy between the theory and the data by testing the hypothesis that young forests extract nitrogen from deep soils, but as the forest ages, re-accumulation of the nitrogen in the soil delays the loss of nitrogen in drainage water. The hypothesis will be tested by a field experiment to determine the propensity for nitrogen accumulation in soil beneath forest stands of different ages, and careful accounting of the amount of nitrogen in a sequence of forests ranging from 15 to over 200 years old. In addition, a computer simulation model of forest ecosystems will be revised to incorporate these new observations. This work is important for management of forests to minimize loss of nitrogen, a key plant nutrient. Air pollution adds excess nitrogen to the forest, and if it is lost in drainage water, it can pollute streams and lakes. The project will involve training of two graduate students and two postdoctoral associates, and a teacher training module will help two high school science teachers develop a unit for teaching about forest ecology in their classrooms.