Collaborative Research: Belowground drivers of aboveground nutrient cycling and productivity in growing forests

年轻的、快速生长的森林可以封存大量的碳，但这种潜力预计最终将受到生物质生长所需营养的限制。考虑到它们的年龄和可用的土壤养分，一些森林的生产力比预期的要高。例如，在低地哥斯达黎加，试验性种植园在经过22年的生长后，仍然具有很高的生产力，并循环使用大量的氮素。这项研究的主要目的是了解为什么这些热带雨林保持生产力。具体地说，该项目将解决这样的假设，即高产森林为细根和土壤微生物提供更多地下碳。预计地下分配的增加将主要通过细根生长和微生物过程对土壤资源的更大开发来促进养分循环，这些过程反馈刺激地上森林的生长。我们将采用大规模和小规模实验相结合的方法来评估碳分配给根部、共生根部微生物和自由生活的土壤微生物对碳氮循环的影响。这项研究的结果将有助于我们更好地理解热带森林生物地球化学的地下途径，从而提高我们模拟和预测森林在当前和未来全球碳氮循环中的作用的能力。这一新信息将为规划和制定潜在的缓解战略提供信息，以应对大气中二氧化碳的增加。此外，该项目将促进学生指导、实地学生教育和国际合作。为了增加代表不足的群体的参与，将提供一门基于探究的热带野外生物学特别短期课程；本科生将由NSF Louis Stokes联盟的董事确定并招募，以支持威斯康星州和伊利诺伊州的少数群体参与计划。我们的目标是向这些学生介绍生态学，并灌输信心和灵感，鼓励他们申请未来的研究奖学金，并最终进入研究生院。

Young, fast-growing forests can sequester huge amounts of carbon, but this potential is expected to be limited eventually by the nutrients required for biomass growth. Some forests are more productive than expected, given their age and available soil nutrients. In lowland Costa Rica, for example, experimental plantations were still highly productive and cycling large amounts of nitrogen after 22 years of growth. The broad aim of this research is to understand why these tropical forests remain productive. Specifically, this project will address the hypothesis that highly productive forests supply more carbon belowground to fine roots and soil microbes. Increased belowground allocation is expected to promote nutrient cycling largely through greater exploitation of soil resources by fine-root growth and microbial processes, which feed back to stimulate aboveground forest growth. A combination of large-scale and small-scale experimental approaches will be used to evaluate how carbon allocation to roots, symbiotic root microbes, and free-living soil microbes influence carbon and nitrogen cycling.The results of this research will provide an improved understanding of the belowground pathways underlying tropical forest biogeochemistry, thereby advancing our ability to model and predict the role of forests in current and future global carbon and nitrogen cycling. This new information will inform planning and development of potential mitigation strategies in response to increasing atmospheric CO2. Furthermore, the project will facilitate student mentoring, field based student education, and international collaboration. To increase participation by underrepresented groups, an inquiry-based special short course in Tropical Field Biology will be offered; undergraduate students will be identified and recruited by the Directors of NSF Louis Stokes Alliances for Minority Participation Programs for Wisconsin and Illinois. The goal is to introduce these students to ecology and instill confidence and inspiration that will encourage them to apply for future research fellowships, and ultimately to graduate school.