Potential for recovery of arctic tundra from atmospheric nitrogen deposition

这个项目研究北极苔原从大气氮沉降的影响中恢复。在汽车、发电站和工业中燃烧化石燃料会产生氮氧化物。这些气体在大气中传播很长一段距离，然后沉积到地表，在那里氮引起植被和土壤的变化。北极苔原受到来自北半球的空气污染，对其非常敏感。20年前，我们在北极高海拔地区的斯瓦尔巴群岛开始了一项实验，研究氮沉积对冻土带植物的影响。我们在植被上浇灌的氮影响了植物的生理机能和不同物种的丰度；一些物种几乎灭绝，另一些物种却繁衍生息。本实验结果用于设定冻土带氮的“临界负荷”；也就是说，国际上商定的生态系统在被破坏之前可以容忍多少氮的数字。在制定国际污染控制立法时，考虑到所有欧洲生态系统的临界负荷值。我们的北极实验还在继续；三年后，我们停止向一些试验田添加氮，但又过了七年，很明显植被没有恢复。在这个项目中，我们将回到实验中来衡量18年来发生了多少恢复。这很重要，因为国际立法已经减少了整个欧洲的氮氧化物排放，我们需要了解一旦沉积在生态系统上的氮量减少，生态系统恢复的潜力是什么。如果结果显示恢复非常缓慢，考虑到氮沉积引起的生态变化不易逆转，可能会降低冻土带氮的临界负荷。

This project investigates the recovery of arctic tundra from the effects of atmospheric nitrogen deposition. Fossil fuel burning in vehicles, power stations and industry produces nitrogen oxides. These gases travel long distances in the atmosphere before being deposited back to the ground surface where the nitrogen causes changes to the vegetation and soil. The arctic tundra receives such air pollution from around the northern hemisphere and is very sensitive to it. Twenty years ago we began an experiment on Svalbard, in the high Arctic, to investigate the effects of nitrogen deposition on tundra plants. The nitrogen that we watered onto the vegetation affected the physiology of plants and the abundance of different species; some species almost died out, others thrived. The results of this experiment were used to set the 'critical load' of nitrogen for tundra; that is, the internationally agreed number for how much nitrogen the ecosystem can tolerate before it is damaged. Critical load values for all European ecosystems were taken into account in the development of international pollution control legislation. Our Arctic experiment continued; after three years we stopped adding nitrogen to some of our experimental plots but after another seven years it was clear that the vegetation had not recovered. In this project we will return to the experiment to measure how much recovery has occurred over 18 years. This is important because international legislation has reduced nitrogen oxide emissions across Europe and we need to understand what the potential is for ecosystems to recover once the amount of nitrogen being deposited on them decreases. Should the results show that recovery is very slow, it is possible that the critical load of nitrogen for tundra will be reduced to take into account the fact that ecological changes caused by nitrogen deposition are not readily reversible.