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

将研究植物碳从根到土壤的移动，以及这种碳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的同位素示踪剂来跟踪14CO2和5NH4在种植黄松和无芒雀麦的根室(根管)中的移动和转化。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根据植物的根来确定。这些微生物的代谢状态将使用生命染色和显微放射自显影技术进行评估。氮矿化和固定化将通过短期的15N池稀释实验来确定。这些研究的结果将被用来比较根际微生物和土壤微生物的代谢状况，并确定微生物在土壤-根界面对植物养分的竞争对这些模式系统的重要性。该项目的意义在于，它将为今后关于植物根部碳与植物可利用氮量之间关系的工作提供一个有价值的数据库；也就是说，它将导致对土壤系统中控制N有效性的因素的深入了解。这是一个重要的问题，因为在全世界的生态系统中，氮往往是限制植物生长的养分。加州大学伯克利分校的设备非常适合这类研究。费尔斯通博士是一流的科学家和教师，这一领域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，就已经发表了三本书，证明她是一个很有前途的学生。

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.