Biological Controls on Nitrate Retention in Northeastern Forest Ecosystems

最近有报告说，大量硝酸盐从森林出口到 地表沃茨引起了人们对硝酸盐损失关注 与相关的酸性和阳离子，可能会导致逐渐 森林土壤肥力下降和水生生物减少 森林集水区下游的生态系统， 富营养化和酸化。 现场实验将 进行：1）量化和比较硝酸盐保留 森林生态系统的能力 东北地区; 2）比较不同土壤类型对硝酸盐吸收的重要性， 生长植被与硝酸盐固定化分解 有机质作为过量硝酸盐的汇; 3）相关树木 物种生长速率和氮利用效率， 铵有效性 这项工作将利用两个正在进行的研究 项目 一个是美国环保署的流域管理项目（WMP）， 一项大型的多研究者研究， 硫酸沉降对土壤生态地球化学过程的影响， 土壤溶液化学在地块和集水水平在一个 缅因州的混合物种森林。 另一个是情节级别N 在哈佛森林NSF-LTER进行的富集实验 在马萨诸塞州的一个地点，调查人员正在研究 长期施氮对氮循环速率的影响 生产力和冠层化学。 环保署的现场项目 提供了一个独特的机会来追踪路径， 硝酸盐对森林生态系统的影响。 这个项目 将支持N同位素研究，这将允许这一点。 来自WMP样地的土壤和组织的初步15 N分析 表明这里提出的技术的高灵敏度将 允许量化重要生态系统中的硝酸盐保留 件. 这项研究将提高我们对 森林生态系统的过程是重要的控制 向河流、湖泊和河口输出硝酸盐和酸度 生态系统 它也将提高我们预测变化的能力 在森林生产力中， 由于自然过程和人为造成的N沉积。

Recent reports of large nitrate exports from forests to surface waters raise concern that losses of nitrate, together with associated acidity and cations, may result in gradual decrease in forest soil fertility and impoverishment of aquatic ecosystems downstream of forested catchments through eutrophication and acidification. Field experiments will be conducted to: 1) quantify and compare nitrate retention capacities of several different forest ecosystems in the Northeast; 2) compare the importances of nitrate uptake by growing vegetation vs. nitrate immobilization in decomposing organic matter as sinks for excess nitrate; and 3) relate tree species growth rates and N use efficiencies to both nitrate and ammonium availabilities. The work will take advantage of two on-going research projects. One is the EPA's Watershed Manipulation Project (WMP), a large multiple-investigator study of the effects of nitric and sulfuric acid deposition on soil biogeochemical processes and soil solution chemistry at both plot and catchment levels in a mixed-species forest in Maine. The other is a plot-level N enrichment experiment conducted at the Harvard Forest NSF-LTER site in Massachusetts where investigators are now studying the effects of chronic N additions on N cycling rates, primary productivity, and canopy chemistry. The in-place, EPA project provides a unique opportunity to trace the paths and to identify the fate of nitrate additions to forest ecosystems. This project will support N isotope studies that will allow for this. Preliminary 15N analysis of soils and tissues from the WMP plots show that the high sensitivity of techniques proposed here will allow for quantifying nitrate retention in important ecosystem components. This research will improve our basic understanding of forest ecosystem processes that are important in controlling exports of nitrate and acidity to stream, lake, and estuarine ecosystems. It will also improve our ability to predict changes in forest productivity as patterns and rates of N cycling change due to both natural processes and human caused N deposition.