Biogeochemical Controls on Nitrogen Fixation in a Diverse Neotropical Forest

生物地球化学对不同新热带森林固氮作用的控制，普林斯顿大学，Lars Hedin和Anne Kraepiel热带森林中和未来二氧化碳温室气体排放的能力关键取决于这些森林是否会越来越受到土壤养分的限制。 该项目将在巴拿马热带森林中使用最先进的措施，以研究对CO2的反应的一个关键组成部分：热带森林中土壤微生物和某些高等植物从大气中自然获取（或“固定”）必需营养氮的能力。 对于固氮作用是否会随着其他营养物质对固氮剂的严重限制而减少，主要科学家之间存在相当大的争议。 然而，几乎没有第一手的了解，决定热带森林固氮率的因素。 该项目将使用直接的固氮措施，结合氮，磷和钼等营养物质的操作，以检查和量化这些因素。 NOAA/GFDL地球系统模型的最新运行表明，解决碳和气候问题（即，如果热带地区受到营养物质的严重限制，那么在未来50年内，稳定在500 ppm大气CO2下的难度将增加一倍。这意味着热带森林中营养物质的作用是我们理解二氧化碳温室气体排放如何影响未来地球气候系统的最大不确定性之一。 该项目是基础科学（即，基本自然过程的研究）对气候变化等实际问题具有直接和潜在的深刻影响。 如果该项目成功地理解了对固氮作用的控制，就有可能将这些过程纳入全球地球系统模型，这反过来又将有助于减少关于未来是否存在二氧化碳排放的自然汇的重大不确定性。

Biogeochemical Controls on Nitrogen Fixation in a Diverse Neotropical Forest.Lars Hedin and Anne Kraepiel, Princeton University The ability of tropical forests to neutralize future emissions of CO2 greenhouse gases depends critically upon whether these forests will become increasingly limited by soil nutrients. This project will use state-of-the art measures in Panamanian tropical forests to examine a crucial component of the response to CO2: the ability of soil microbes and certain higher plants in tropical forests to naturally acquire (or 'fix') the essential nutrient nitrogen from the atmosphere. There is considerable controversy among leading scientists as to whether or not nitrogen fixation will decrease as other nutrients become severely limiting to nitrogen fixers in response to climate change. However, there exists virtually no first-hand understanding of the factors that determine nitrogen fixation rates in tropical forests. This project will use direct measures of nitrogen fixation in combination with manipulations of nutrients including nitrogen, phosphorus and molybdenum, to examine and quantify these factors. Recent runs of the NOAA/GFDL earth system model show that solving the carbon and climate problem (i.e., stabilization at 500 ppm atmospheric CO2) is fully twice as difficult over the next fifty years if the tropics become severely limited by nutrients. This means that the role of nutrients in tropical forests constitutes one of the greatest uncertainties in our understanding of how CO2 greenhouse gas emissions will affect the Earth's climate system in the future. This project is an example of how basic science (i.e., the study of fundamental natural processes) has immediate and potentially deep implications for practical issues such as climate change. If the project is successful in understanding controls on nitrogen fixation, it becomes possible to incorporate these processes in the global earth system models, which, in turn, will contribute to reducing a major uncertainty about the existence of future natural sinks for CO2 emissions.