Soil ammonium: BioCON : Biodiversity, Elevated CO2, and N Enrichment

BioCON (Biodiversity, CO2, and Nitrogen) is an ecological experiment started in 1997 at the University of Minnesota's Cedar Creek Ecosystem Science Reserve. BioCON's goal is to explore the ways in which plant communities will respond to three environmental changes that are known to be occurring on a global scale: increasing nitrogen deposition, increasing atmospheric CO2, and decreasing biodiversity. Why Biodiversity, CO2, and Nitrogen? While there are many uncertainties in global change biology, there are also some well documented facts. Some of these are: 1. The amount of carbon dioxide (CO2) in the atmosphere is rising. Since the industrial revolution, the CO2 concentration in the atmosphere has increased from approximately 275 parts per million (ppm) to about 378 ppm today. This has been largely the result of fossil fuel burning. It is expected that CO2 levels will continue to rise, and that by the year 2050 these levels will be approximately 550 ppm. CO2 is the raw material for photosynthesis and is known to affect plant growth and development. 2. The amount of nitrogen moving through terrestrial ecosystems has increased in the recent past. While natural "background" levels of nitrogen fixation have remained constant, human additions to the system through fertilizer production and fossil fuel use have increased dramatically. Nitrogen is a key nutrient for plant growth and plays a critical role in plant community structure and composition in many environments. 3. Biodiversity levels are falling. While the research and data are not as complete as they are for CO2 and nitrogen, data indicate that the number of species globally, is being reduced. Perhaps more important for ecosystem function, diversity levels on local to regional scales have fallen due to land use change, biotic invasion and many other drivers. While much is known about how each of these factors affects ecosystem functioning, many questions remain. There is also little data on how these issues affect each other, and what emergent qualities may arise when systems are exposed to these changes simultaneously. BioCON seeks to address these issues with this multi-year study at Cedar Creek Ecosytem Science Preserve.BioCON（生物多样性、二氧化碳与氮素）是1997年于美国明尼苏达大学雪松溪生态系统科学保护区（Cedar Creek Ecosystem Science Reserve）启动的一项生态学实验。该实验旨在探究植物群落对三种已知正在全球范围内发生的环境变化的响应模式：氮沉降增加、大气CO₂浓度升高以及生物多样性丧失。 为何聚焦生物多样性、二氧化碳与氮素？ 全球变化生物学领域虽尚存诸多不确定性，但亦存在诸多已有充分实证支撑的科学事实，具体如下： 1. 大气中二氧化碳(CO₂)的含量持续攀升。自工业革命以来，大气CO₂浓度已从约275百万分比浓度(parts per million, ppm)升至当前的约378 ppm，这一现象主要源于化石燃料燃烧。据预测，CO₂浓度将持续上升，至2050年左右将达到约550 ppm。CO₂是光合作用的原料，已知可影响植物的生长与发育。 2. 近几十年来，流经陆地生态系统的氮素总量有所增加。尽管自然“本底”固氮水平保持稳定，但人类通过化肥生产与化石燃料使用向生态系统输入的氮素已大幅增长。氮素是植物生长的关键营养元素，在诸多生境中对植物群落结构与组成发挥着至关重要的作用。 3. 生物多样性水平正持续下降。尽管相关研究与数据不如CO₂和氮素领域那般完备，但现有数据显示全球物种数量正在减少。或许对生态系统功能而言更为关键的是，受土地利用变化、生物入侵及其他诸多驱动因子影响，局地至区域尺度的生物多样性水平已出现下滑。 尽管学界对上述各因素如何影响生态系统功能已有诸多认知，但仍存在大量未决问题。目前关于这些因素间的相互作用机制，以及生态系统同时暴露于这些变化时可能产生的涌现特性，相关数据仍十分匮乏。BioCON项目旨在通过在雪松溪生态系统科学保护区开展的这项多年期研究，对上述问题进行探究。