Percent light penetration: 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.

生物多样性、二氧化碳与氮素（BioCON）是1997年于明尼苏达大学雪松溪生态系统科学保护区启动的一项生态学实验。本实验旨在探究植物群落对全球范围内正在发生的三类环境变化的响应机制，这三类变化分别为：氮沉降加剧、大气二氧化碳浓度升高以及生物多样性丧失。

为何选取生物多样性、二氧化碳与氮素作为研究对象？尽管全球变化生物学领域尚存诸多不确定性，但也存在若干已被充分证实的事实。其中包括：
1. 大气中的二氧化碳（CO₂）浓度持续上升。自工业革命以来，大气CO₂浓度已从约275 ppm（百万分比浓度）升至如今的约378 ppm，这在很大程度上源于化石燃料燃烧。据预测，CO₂浓度仍将持续攀升，到2050年或将达到约550 ppm。CO₂是光合作用的原料，已知其会对植物的生长与发育产生影响。
2. 近年来，流经陆地生态系统的氮素总量有所增加。尽管自然的“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添加的氮素已大幅增长。氮素是植物生长的关键营养元素，在多数环境中对植物群落结构与组成发挥着至关重要的作用。
3. 生物多样性水平正在下降。尽管相关研究与数据不如CO₂和氮素领域那般完备，但现有数据表明，全球物种数量正逐步减少。或许对生态系统功能而言更为关键的是，由于土地利用变化、生物入侵及其他诸多驱动因素，局地到区域尺度的生物多样性水平已出现下降。

尽管学界对上述各因素如何影响生态系统功能已具备不少认知，但仍有诸多问题有待解答。同时，关于这些因素之间如何相互影响，以及生态系统同时暴露于这些变化时可能产生哪些涌现特性的相关数据仍十分匮乏。本实验旨在通过这项在雪松溪生态系统科学保护区开展的多年期研究，对上述问题展开探索。