Collaborative Research: Organic Nitrogen Cycling in Northern Hardwood - Conifer Forests

目前美国东北部森林氮素循环的概念模型强调了无机氮形态(即铵和硝酸盐)对树木生长和森林生产力的重要性。然而，有机形态的氮也被植物吸收。这项建议的总体目标是量化有机氮在美国东北部温带森林生态系统中作为营养源的重要性。为了实现这一目标，将研究影响土壤中有机氮生产和周转的因素，特别是氨基酸和氨基糖。将对有机氮的生产和周转之间的平衡进行评估，以确定优势树种吸收的氮的类型和形式。这些目标将通过在康涅狄格州西部和马萨诸塞州两种土壤母质上的单一树种林中建立植物来实现。田间和实验室研究将被用来测量土壤中有机氮的池、通量和吸收。土壤中氮的有效性限制了森林生态系统的生产力及其隔离二氧化碳浓度上升的能力，二氧化碳是一种温室气体。通过了解影响林木吸收N的形式和数量的因素，这项建议将阐明调节一种关键的生长限制土壤资源的可用性的过程，以及可以在多大程度上依赖森林生态系统从地球大气中吸收二氧化碳。

The current conceptual model for the nitrogen (N) cycle of northeastern US forests stresses the importance of inorganic N forms (i.e., ammonium and nitrate) for tree growth and forest productivity. However, organic forms of N are also be taken up by plants. The overall objective of this proposal is to quantify the importance of organic N as a nutrient source in temperate forest ecosystems of the northeastern U.S. To achieve this objective, the factors that affect the production and turnover of organic N in the soil will be studied, focusing specifically on amino acids and amino sugars. The balance between the production and turnover of organic N will be assessed to determine the types and forms of N taken up by dominant tree species. These objectives will be met by establishing plants in single-species stands on two types of soil parent materials in western Connecticut and Massachusetts. Field and laboratory studies will be used to measure the pools, fluxes and uptake of organic N in the soil. The availability of N in the soil limits the productivity of forest ecosystems and their capacity to sequester rising concentrations of carbon dioxide, a greenhouse gas. By understanding the factors that affect the form and the quantity of N taken up by forest trees, this proposal will shed light on the processes regulating the availability of a key growth limiting soil resource and the degree to which forest ecosystems can be relied upon to absorb CO2 from the earth's atmosphere.