Potential for recovery of arctic tundra from atmospheric nitrogen deposition

本计画调查北极苔原受大气氮沈积影响之复原。车辆、发电站和工业中燃烧的化石燃料会产生氮氧化物。这些气体在大气中传播很长的距离，然后沉积到地面，氮导致植被和土壤发生变化。北极苔原受到来自北方的这种空气污染，对它非常敏感。20年前，我们开始在北极高纬度地区的斯瓦尔巴特群岛进行一项实验，研究氮沉降对苔原植物的影响。我们浇灌在植被上的氮影响了植物的生理和不同物种的丰富程度;一些物种几乎灭绝，另一些则蓬勃发展。这项实验的结果被用来设定冻原氮的“临界负荷”;也就是说，国际上公认的生态系统在受到破坏之前可以承受多少氮的数量。在制定国际污染控制立法时考虑到了欧洲所有生态系统的临界负荷值。我们的北极试验继续进行;三年后，我们停止在一些试验田里施氮，但又过了七年，植被显然没有恢复。在这个项目中，我们将回到实验，以衡量有多少恢复发生了18年。这一点很重要，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。如果结果表明恢复非常缓慢，则可能会降低冻原的氮临界负荷，以考虑到氮沉降引起的生态变化不容易逆转的事实。

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.