Soil moisture: 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, Biodiversity, CO2, and Nitrogen）实验是一项始于1997年的生态学野外实验，选址于明尼苏达大学雪松溪生态系统科学保护区。该实验的核心目标是探究植物群落对三类已被证实正全球发生的环境变化的响应机制，这三类变化分别为：氮沉降增加、大气CO₂浓度升高以及生物多样性丧失。

为何选取生物多样性、CO₂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科学事实，具体如下：
1. 大气中二氧化碳（CO₂）浓度持续攀升。自工业革命以来，大气CO₂浓度已从约275百万分比浓度（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浓度仍将持续上升，至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. 近期陆地生态系统中的氮素流通量显著增加。尽管自然状态下的“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投入的氮素已大幅增长。氮素是植物生长的关键营养元素，在多数生境中对植物群落结构与组成均发挥着至关重要的作用。
3. 生物多样性水平持续下降。尽管相关研究与数据尚不如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。而对生态系统功能而言或许更为关键的是，受土地利用变化、生物入侵及其他诸多驱动因素影响，局地至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单独影响生态系统功能已有较多认知，但仍有大量问题有待解答。此外，关于这些因素之间的相互作用，以及当生态系统同时暴露于这些变化时可能涌现的新特性，相关数据仍十分匮乏。BioCON实验正是旨在通过在雪松溪生态系统科学保护区开展的多年期研究，对上述问题进行探索与解答。