Is plant biodiversity loss and recovery in N polluted ecosystems regulated by phosphorus acquisition?

化石燃料燃烧和农业向大气排放的氮(N)增加，增加了这些N向生态系统沉积的速度。这些增加的氮沉积速率是全球生态系统生物多样性丧失的最重要原因之一。例如，在北欧，许多最先获得这些高N投入的生态系统(如物种丰富的草原)已经失去了许多生物多样性，包括稀有或受保护物种的丧失。因此，最重要的是，我们要了解推动这一物种变化的机制，使我们能够预测对生态系统的影响，并更好地管理和恢复已经受到污染的系统。在生态系统中，磷通常是决定植物生长的最重要或次要的营养物质。因此，氮污染对植物磷吸收的影响可能会对植物的生长产生重大影响，从而改变植物群落的生物多样性。最近的证据表明，这种情况可能正在发生。特别是，物种丰富的石灰性草原的主要植物类型在N污染下表现出相当大的丰度变化(莎草和草的丰度增加，减少了草本植物的多样性，包括许多具有保护重要性的诱人的花朵)。重要的是，这些主要植物类群有不同的磷吸收方法。莎草(以及程度较小的禾本科植物)具有特殊的根系适应性，而杂草则依赖菌根共生来获取磷。因此，很明显，氮污染对这些不同的磷吸收机制的影响可能会推动物种的变化。利用植物区系丰富的石灰质草原(英国德比郡山顶地区国家公园)，这项研究计划将是第一次确定和比较N沉降对主要植物类型内磷吸收的独特机制的影响。它将确定氮沉积对植物磷供应的影响，并确定这些影响是否可以驱动物种变化。它还将决定，当氮沉积由于有效的控制措施而下降时，植被是否能够从这些对磷供应的影响中恢复过来。这项工作对那些关心保护生态系统和保护生物多样性的人具有相当重要的意义。它将向政策制定者通报污染物N负荷的影响，使我们能够更好地预测污染物N对生态系统的影响，并更好地建立“临界负荷”。这种机械性的理解还将为全球其他相关系统如何应对污染物N负荷提供重要的见解，特别是在其他系统中，磷供应是决定植物生长的最重要因素。

Increased emissions of nitrogen (N) to the atmosphere from fossil fuel burning and agriculture are increasing the rates of deposition of this N to ecosystems. These increased rates of N deposition are one of the most important causes of biodiversity loss in ecosystems at a global scale. Within northern Europe, for example, many ecosystems first to receive these high N inputs (such as species rich grasslands), have lost much biodiversity, including loss of rare or protected species. It is most important, therefore, that we understand the mechanisms that drive this species change, both to allow us to predict impacts on ecosystems, and better manage and restore already polluted systems. In ecosystems, phosphorus (P) is generally the most or second most important nutrient for determining the growth of plants. An impact of N pollution on plant P uptake could therefore significantly impact on plant growth and therefore also alter the biodiversity of plant communities. Recent evidence suggests that this may be happening. In particular, the major plant types of species rich calcareous grasslands show considerable change in abundance under N pollution (sedges and grasses increase in abundance which reduces the diversity of herbaceous plants, including many attractive flowers that give these grasslands their conservation importance). Importantly, these major plant groups have contrasting methods of P uptake. Sedges (and to a lesser extent grasses) have special root adaptations while forbs are reliant on mycorrhizal symbioses to acquire P. It is therefore apparent that N pollution impacts on these contrasting P uptake mechanisms could drive species change. Using a floristically rich calcareous grassland (Peak District National Park, Derbyshire, UK), this programme of research will be the first study to determine and compare the impacts of N deposition on the distinctive mechanisms of P acquisition within the major plant types. It will determine the impacts of N deposition on plant P supply and determine whether these impacts can drive species change. It will also determine whether vegetation can recover from these impacts on P supply when N deposition declines as a result of effective control measures. The work is of considerable importance to those concerned with the conservation of ecosystems and preservation of biodiversity. It will inform policy makers of the impacts of pollutant N loading and allow us to better predict pollutant N impact on ecosystems and better establish 'critical loads'. The mechanistic understanding will also provide important insight into how other related systems around the globe may respond to pollutant N loading, particularly other systems where P supply is the most important factor in determining plant growth.