International Research Fellowship Program: Does the Foliar Nitrogen Isoptope Variability in Rain Forest Trees Reflect Niche Partitioning, Biophysical Processes or Climate?

国际研究奖学金计划使美国科学家和工程师能够在国外进行9至24个月的研究。 该计划的奖项提供了联合研究的机会，以及使用国外独特或互补的设施，专业知识和实验条件。 该奖项将支持Jordan Mayor博士与Benjamin Turner博士在巴拿马史密森尼热带研究所开展为期24个月的研究。 植物氮素的有效性是世界上许多地区森林生产力和生态系统动态的主要控制因素。 热带森林被认为是相对丰富的N，但其生长和适应性的自然和人为的N循环和气候的变化作出反应。 由于氮循环的复杂性和各种类型的植物对氮限制的反应，有一个强烈的研究需要使用的重，轻稳定同位素测量的N的比例，以整合两个地球化学过程和植物群落对氮的波动的响应。 然而，要有信心在使用和解释叶片氮同位素比值，基本的机械过程必须得到更好的理解。 PI，而住在本杰明·特纳博士的土壤生物地球化学实验室内，将满足上述研究需要，通过测量稳定同位素比率从所有三种形式的植物有效土壤氮，沿着树根和树叶组织，在整个巴拿马雨林的三个实验系统。 实验系统的选择，以针对主要的假设控制植物N同位素值：降水，土壤养分的生物利用度，和类型的根相关的菌根真菌。 三个实验系统的目的是针对特定的假设，并结合起来，提供了一个统一的理论在热带森林树木N同位素模式的变异性的原因。 人类活动可以增加生态系统中氮的可用性，通过增加肥料或大气沉积增加氮的输入，或通过加速内部循环的N作为气候变化或景观退化的结果。 这项联合研究将为解释相对简单的叶分析提供信息，以便更好地理解N周期中复杂的时间综合差异，并容易检测到它们的变化。 在全球迅速变化的时代，这些自然指数无疑将证明对森林监测工作有用。 除了区分树的N同位素比的根本原因全球的好处，这些数据也将允许测试树的专业化对特定形式的土壤N -一个假设的机制，允许共存，而不是竞争性排斥，否则类似的树种在生物多样性的雨林。

The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a 24-month research fellowship by Dr. Jordan Mayor to work with Dr. Benjamin Turner at the Smithsonian Tropical Research Institute in Panama. The availability of nitrogen (N) to plants is a primary control over forest productivity and ecosystem dynamics throughout much of the world. Tropical forests are presumed to be relatively N-rich yet their growth and adaptations respond to natural and anthropogenic changes in N-cycling and climate. Due to the complexity of the N cycle and the various types of plant responses to N limitations, there is a strong research need to use the ratio of heavy to light stable isotope measurements of N to integrate both biogeochemical processes and plant community responses to fluctuations in N availability. However, to be confident in the use and interpretation of foliar N isotope ratios, underlying mechanistic processes must be better understood. The PI, while housed within the Soils Biogeochemistry laboratory of Dr. Benjamin Turner, will meet the above research need by measuring stable isotope ratios from all three forms of plant available soil N, along with tree root and leaf tissue, across three experimental systems throughout Panamanian rainforest. The experimental systems were selected to target the main hypothesized controls over plant N isotope values: precipitation, soil nutrient bioavailability, and the type of root-associated mycorrhizal fungi. Each of the three experimental systems is designed to target specific hypotheses and, when combined, provide for a unified theory on the causes of variability in tree N isotope patterns in tropical forests. Human activities can increase N availability in ecosystems either by increasing N inputs through fertilizer addition or atmospheric deposition, or by speeding up internal recycling of N as a result of altered climate or landscape degradation. This joint research will inform the interpretation of relatively simple foliar analyses so that complex, time-integrated differences in N-cycles can be better understood and changes to them easily detected. In a time of rapid global change, these natural indexes will undoubtedly prove useful to forest monitoring efforts. In addition to the benefits of differentiating the underlying causes of tree N isotope ratios globally, these data will also permit testing for tree specialization on specific forms of soil N - a hypothesized mechanism for permitting the coexistence, rather than competitive exclusion, of otherwise similar tree species in biodiverse rainforest.