Dissertation Research: Rhizodeposition Control on Spatial Compartmentalization of Active Microorganisms and Nitrogen Mineralization/Immobilization

研究植物碳从根系到土壤的运动及其对土壤中氮矿化和固定过程的影响。实验将使用放射性和稳定同位素示踪剂跟踪14CO2和5NH4在种植黄松和凤尾松的根室（根管）中的运动和转化。微生物的质量和活性将是研究的中心焦点。微生物生物量的空间分布将与植物根系有关。这些微生物的代谢状态将被评估使用生命染色和显微放射自显影。通过短期15N池稀释实验确定氮矿化和固定化。这些研究的结果将用于比较根际和大块土壤微生物的代谢状态，并确定微生物在土壤-根界面对这些模型系统的植物养分竞争的重要性。该项目的意义在于，它将为未来研究植物根系碳与植物可利用氮量之间的关系提供有价值的数据基础；也就是说，它将导致洞察是什么控制了土壤系统中的氮有效性。这是一个重要的问题，因为在世界范围内的生态系统中，氮通常是限制植物生长的养分。加州大学伯克利分校（University of California, Berkeley）的设施非常适合这类研究。费尔斯通博士是一流的科学家和教师，这方面的研究是她的专长之一。诺顿女士在开始她的博士工作之前就已经发表了三篇论文，这表明她是一个有前途的学生。

The movement of plant carbon from roots into the soil and the effects of this carbon on nitrogen mineralization and immobilization processes in the soil will be studied. Experiments will be performed using radioactive and stable isotope tracers to follow the movement and transformations of 14CO2 and 5NH4 in root chambers (rhizotrons) planted with Pinus ponderosa and Bromus mollis. The mass and activity of microorganisms will be a central focus of the research. The spatial distribution of microbial biomass will be determined in relation to plant roots. The metabolic state of these microorganisms will be assessed using vital stains and microautoradiography. Nitrogen mineralization and immobilization will be determined using short-term 15N pool dilution experiments. Results from these studies will be used to compare the metabolic status of rhizosphere and bulk soil microorganisms and to determine the importance of microbial competition for plant nutrients at the soil-root interface for these model systems. The significance of this project is that it should yield a valuable data base for future work on the relationship between plant carbon from roots and the amount of N available to plants; that is, it will lead to insight as to what controls N availability in soil systems. This is an important issue since N is often the nutrient limiting plant growth in ecosystems world- wide. The facilities at the University of California, Berkeley, are excellent for this type of research. Dr. Firestone is a first-rate scientist and teacher and this area of research is one of her specialties. Ms. Norton shows all evidence of being a promising student with three publications to her credit even before beginning her doctoral work.