Atmospheric nitrogen deposition is the third largest cause of global biodiversity loss, with rates that have more than doubled over the past century. This is especially threatening for tropical regions where the deposition may soon exceed 25 kg of N ha−1 year−1, well above the threshold for physiological damage of 12–20 kg of N ha−1 year−1, depending on plant species and nitrogenous compound. It is thus urgent to monitor these regions where the most diverse biotas occur. However, most studies have been conducted in Europe, the USA and recently in China. This review presents the case for the potential use of biological organisms to monitor nitrogen deposition, with emphasis on tropical plants. We first present an overview of atmospheric chemistry and the nitrogen metabolism of potential biomonitors, followed by a framework for monitoring nitrogen deposition based on the simultaneous use of various functional groups. In particular, the tissue nitrogen content responds to the rate of deposition, especially for mosses, whose nitrogen content increases by 1‰ per kilogram of N ha−1 year−1. The isotopic signature, δ15N, is a useful indicator of the nitrogen source, as the slightly negative values (e.g. 5‰) of plants from natural environments can become very negative (−11.2‰) in sites with agricultural and husbandry activities, but very positive (13.3‰) in urban environments with high vehicular activity. Mosses are good biomonitors for wet deposition and atmospheric epiphytes for dry deposition. In turn, the nitrogen saturation of ecosystems can be monitored with trees whose isotopic values increase with saturation. Although given ecophysiological limitations of different organisms, particular studies should be conducted in each area of interest to determine the most suitable biomonitors. Overall, biomonitors can provide an integrative approach for characterizing nitrogen deposition in regions where the deployment of automated instruments or passive monitoring is not feasible or can be complementary.
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机译：大气氮沉积是造成全球生物多样性丧失的第三大原因，在过去一个世纪中，氮的沉积速度增加了一倍以上。这对于热带地区尤其具有威胁，在热带地区沉积物可能很快超过25 kg N ha -1 年 -1 ，远高于生理损害阈值12–20 kg N ha -1 年 -1 的时间取决于植物种类和含氮化合物。因此，迫切需要监测这些生物群最多的地区。但是，大多数研究已在欧洲，美国以及最近在中国进行。这篇综述介绍了潜在利用生物有机体监测氮沉积的案例，重点是热带植物。我们首先介绍一下大气化学和潜在生物监测器的氮代谢，然后介绍一个基于同时使用各种官能团的监测氮沉积的框架。尤其是组织中的氮含量对沉积速率有响应，特别是对于苔藓而言，其每千克N ha -1 年 -1 的氮含量增加1‰。同位素特征δ 15 N是氮源的有用指标，因为自然环境中植物的负值（例如5‰）可能会在站点中变为非常负值（-11.2‰）。农业和畜牧业活动，但在汽车活动频繁的城市环境中非常积极（13.3‰）。苔藓是用于湿沉降的良好生物监测剂，而对于干沉降则是大气附生植物。反过来，可以用树木的同位素值随饱和度增加而监测生态系统的氮饱和度。尽管考虑到不同生物的生态生理限制，但应该在每个感兴趣的领域中进行特定的研究，以确定最合适的生物监控器。总体而言，生物监测器可以提供一种综合方法来表征在自动化仪器或被动监测的部署不可行或可以互补的区域中氮沉积的特征。
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