Activity and Survival of Frankia in Soil

法兰克属植物在土壤中作为固氮剂的重要性，以及法兰克属植物在造林领域的应用前景具有重要的生态意义。本研究将重点研究法兰克腐生生长和根际对其代谢活性的影响。一个区分土壤中法兰克属生理类别的概念模型将指导检验法兰克属在土壤中腐生生长的假设。量化Frankia种群（生物量）和土壤感染单位变化的方法将包括使用DNA探针和限制性片段长度多态性（RFLP）分析来鉴定和追踪低水平接种到非无菌土壤系统中的Frankia菌株。聚合酶链反应作为一种手段，以提高这种方法的敏感性将被使用。测试法兰克菌腐生能力的实验包括接种低水平的非无菌土壤，在桤木亲和性组中纯培养孢子阴性型法兰克菌。将测量其种群生物量（DNA含量）和感染单位数（MPN生物测定）随时间的变化。变量包括红桤木、黄桦和道格拉斯冷杉三种植物的根际土壤和非根际土壤，以检验寄主或非寄主植物的根际土壤是否促进法兰克腐生生长。孢子作为感染单位的作用将通过实验来检验根际是否刺激孢子萌发。

The importance of Frankia as a nitrogen fixer in soils, and the future of Frankia in the area of silviculture is of ecological significance. This proposal will focus on the saprophytic growth and the influence of the rhizosphere on metabolic activity of Frankia. A conceptual model distinguishing physiological classes of Frankia in soil will guide testing of the hypothesis that Frankia can grow saprophytically in soil. Methods that quantify changes in the Frankia population (biomass) as well as infective units in soil, will include use of DNA probes and restriction fragment length polymorphism (RFLP) analysis to identify and trace a Frankia strain inoculated at low levels into a non-sterile soil system. Polymerase chain reactions as a means to increase the sensitivity of such methods will be used. The experiment to test for Frankia saprophytic competence involves inoculation of non-sterile soil at low levels with a pure culture of a spore-negative type of Frankia in the alder compatability group. Changes in its population biomass (DNA content) and numbers of infective units (MPN bioassay) with time will be measured. Variables include rhizosphere vs. non- rhizosphere soil for three plant species: red alder, yellow birch and Douglas-fir, to test if rhizosphere soil of host or non-host plants promote saprophytic growth of Frankia. The role of spores as infective units will be examined by experiments to test whether rhizosphere stimulates spore germination.