Collaborative Research: Disrupted Nitrogen Cycles in the Brazilian Amazon

提供资金用于研究巴西亚马逊地区的氮(N)循环。这项研究旨在量化新热带地区自然和农业环境中氮素的转化和运输途径。农业的转移加上热带地区氮肥投入的增加，有可能导致一氧化二氮向大气中的大量损失，或增加向河流和溪流中的可溶性氮的移动。拟议的实地研究将量化包气带、地下水和自然条件下(热带森林)、大豆单作以及大豆和玉米两熟种植下的N2O通量和N的去向。遥感将被用于将实地和模型的结果放大到亚马逊地区，并将研究成果纳入动态植被模型(IBIS)，该模型已经为亚马逊地区设定了参数，并将用于估计未来不同气候和土地利用管理情景下的N排放。这项工作将检验两个假设：(1)与天然林相比，增加氮肥将导致适度但不是很大的N2O排放，因为土壤排水良好，预计不会有足够长的厌氧时间来积累N2O；(2)由于玉米作物对氮肥的高吸收速率，以及通过阴离子交换将残留的N淋滤液保留在深层粘性土壤中，氮素在施氮肥的地块中损失最小。这项研究将有助于了解改变农业做法对亚马逊地区温室气体排放和溪流污染的影响。与巴西当地科学家的合作以及对美国和巴西学生的培训将是这项研究的重要影响。将通过已建立的联系定期向巴西的农业生产者和政策制定者介绍成果，并支持一名美国记者访问研究现场，这是长期生态和生物地球化学研究的地点，从而实现公共宣传和成果的广泛传播。

Funds are provided to study nitrogen (N) cycles in the Brazilian Amazon. The research aims at quantifying N transformation and transport pathways in natural and agricultural settings in the Neotropics. The shift in agriculture combined with the increase in nitrogen fertilizer inputs in tropical regions have the potential to drive profound losses of nitrous oxide to the atmosphere, or increased movement of soluble N to rivers and streams. The proposed field research will quantify N2O fluxes and N fate in the vadose zone, groundwater and streams under natural conditions (tropical forest), single cropping of soybeans, and double cropping with soybeans and maize. Remote sensing will be used to scale up results from the field and model to the Amazon region, and incorporation of research results into a dynamic vegetation model (IBIS) that has been parameterized for the Amazon and will be used to estimate N emissions under different climate and land use management scenarios in the future. The work will test two hypotheses: (1) that increased N fertilization will lead to moderately but not greatly higher N2O emissions compared to natural forest because soils are well-drained and are not expected to go anaerobic long enough for accumulation of N2O, and (2) that N losses to streams will be minimal in N-fertilized plots because of high rates of uptake by maize crop and retention of any residual N leachates in deep, clay soils through anion exchange.The research will aid in understanding effects of changing agricultural practices on greenhouse gas emissions and stream pollution in the Amazon. Partnerships with local Brazilian scientists and training of US and Brazilian students will be important impacts from the research. Public outreach and broad dissemination of results will be achieved through regular presentations to agricultural producers and policy makers in Brazil through established contacts, as well as the support of a US journalist to visit the research field sites, which are locations of long-term ecological and biogeochemical research.