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的影响，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。其他环境因素（如氮和水）的未知影响是这种不确定性的主要来源。氮是一种必需的矿质养分，其有效性和利用调节着植物对高CO2的响应。考虑到植物生物学中碳(C)和氮之间的复杂联系，氮的高杠杆作用是偶然的。众所周知，在短期内，植物暴露在高CO2环境中会增强其对C的吸收。然而，从理论上讲，只有那些能够维持氮和碳需求平衡的物种才能维持长期的积极影响。现有的少量数据表明，植物物种对高CO2的氮吸收反应差异很大。然而，从一些实证研究的观察结果不能推断到覆盖全球范围内的广泛物种，我们目前缺乏一个机制的理解来制定这样的路线图。在这里，我们建议利用来自不同生态系统的物种来阐明当二氧化碳浓度升高时控制植物氮吸收的主要机制。我们建议开发生理生化标记，可以用来衡量目标物种维持其N和C平衡的程度。已知这些生理生化标记在自然条件下控制植物对氮的吸收，因此也可能在高CO2条件下控制植物对氮的吸收反应。这些发现对于基础研究和管理/政策问题同样重要，因为它们必须应对日益增长的应对未来气候的压力。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二氧化碳天然温泉以及芝加哥伊利诺伊大学的一些开顶室中进行。这里产生的结果将对旨在预测陆地生态系统在未来气候中的命运的预测模型的发展至关重要。

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.