Do Internal N Signals Regulate Interspecific Variability in N Uptake Response to Elevated CO?

虽然科学家们普遍认为，预计大气中二氧化碳浓度的上升将对陆地生态系统的生产力和组成产生深远影响，但我们可靠地预测这些变化的确切性质的能力仍然很薄弱。氮（N）和水等其他环境因素的未知影响是这种不确定性的主要来源。氮素是一种重要的矿质营养元素，其有效性和利用率调节植物对高CO2的反应。当人们考虑到植物生物学中碳（C）和氮之间的复杂联系时，氮的这种高杠杆作用是偶然的。众所周知，在短期内，暴露于高CO2的植物将提高其C吸收。然而，从理论上讲，只有那些能够维持N和C需求之间的平衡的物种才能维持长期的积极影响。少数可用的数据表明，植物物种在其氮吸收响应高CO2变化很大。然而，从一些经验性研究的观察不能外推到覆盖地球仪周围的广泛物种，我们目前缺乏一个机制的理解，以制定这样的路线图。在这里，我们建议阐明的主要机制（S），控制植物N吸收时，CO2浓度升高，使用对比生态系统的物种。我们建议开发的生理和生化标记，可用于衡量在何种程度上，目标物种可以保持其N和C平衡。这里所针对的生理和生化标志物是已知的，以控制植物氮素吸收在自然条件下，因此很可能控制氮素吸收的反应，以及在高CO2。这些发现对于基础研究和管理/政策问题同样重要，因为这些问题必须应对日益增加的压力，以科普未来的气候。拟议的研究将在六个国家资助的自由空气二氧化碳富集（FACE）实验，意大利和新西兰的两个CO2天然温泉，以及芝加哥伊利诺伊大学的一些开顶室进行。这里产生的结果将是至关重要的预测模型，旨在预测未来气候的陆地生态系统的命运的发展。

While there is a general consensus among scientists that the projected rise in the concentration of atmospheric CO2 will have a profound impact on productivity and composition of terrestrial ecosystems, our capacity to reliably predict the exact nature of these changes remain tenuous. The unknown effects of other environmental factors such as nitrogen (N) and water are major sources of this uncertainty. N is an essential mineral nutrient whose availability and utilization regulates plant responses to high CO2. This high leverage by N is fortuitous when one considers the intricate connection between carbon (C) and N in plant biology. It is well recognized that in the short term, plants exposed to high CO2 will enhance their C uptake. Theoretically, however, only those species that can maintain a balance between N and C demand will sustain a long-term positive effect. The few available data indicate that plant species vary widely in their N uptake responses to high CO2. However, observations from a few empirical studies can not be extrapolated to cover a wide range of species around the globe and we currently lack a mechanistic understanding to develop such a roadmap. Here we propose to elucidate the major mechanism(s) that control plant N uptake when CO2 concentration is elevated using species from contrasting ecosystems. We propose to develop physiological and biochemical markers that could be used to gauge the extent to which a target species can maintain its N and C balance. The physiological and biochemical markers targeted here are known to control plant N uptake under natural conditions and therefore are likely to control N uptake responses under high CO2 as well. The findings are equally important for basic research and management/policy issues that must deal with increasing pressure to cope with the future climate. The proposed research will be conducted at six nationally funded Free Air Carbon dioxide Enrichment (FACE) experiments, two CO2 natural springs in Italy and New Zealand, and a number of open-top chambers at the University of Illinois at Chicago. The results generated here will be critical for the development of predictive models designed to forecast the fate of terrestrial ecosystems in a future climate.