Tracing and evaluating functional root connections among stems within aspen clones

TitleTracing and evaluating functional root connections among stems within aspen clones
Publication TypeThesis
Year of Publication1961
AuthorsDe Byle NValentine
DegreeDoctor of Philosophy
Number of Pages269 pp.
UniversityUniversity of Michigan
CityAnn Arbor, MI

Root suckering of both quaking aspen (Populus tremuloides Michx.) and largetooth aspen (P. grandidentata Michx.) commonly produces clones of genetically identical stems. Due to this origin, the stems in each clone are, to some extent, joined through the parent root system. This study was conducted to clarify and evaluate the physiological importance of these parent root connections, and to determine their persistence through 40 to 50 years of stand age. Data were gathered from aspen clones which had been vegetatively reproducing for one or more generations in northern Lower Michigan. Some root systems were excavated, but the majority of interstem connections were discovered through the use of dye, phytocide, and radioisotope tracers. A number of tracer injection techniques were tested, with the use of cone-frustum reservoirs attached near the bases of stems being found most satisfactory for introducing tracer solutions into donor trees. Tracers were inoculated into more than 120 largetooth aspen clones which were divided among 3 age classes, ranging from 6 to 40 years, on 4 sites. Excavation of root systems revealed parent root connections among largetooth aspen stems up to 50 years old. A number of dead stumps with live root systems, which were in turn joined to living trees through the parent roots, existed on these exposed anastomotic networks. Excavation on one site exposed root grafts that had united several 40-year old largetooth aspen trees with their neighbors. Eosin bluish dye and sodium arsenite were the best tracers. Both were readily absorbed by the xylem of the donor trees and transported through the roots to attached receptor trees in which their presence was visibly evident. Radioactive rubidium-86 could only be detected in receptors through time-consuming monitoring. There were 105 receptor trees distributed among 71 largetooth aspen clones injected with eosin, 48 receptors among 24 clones injected with sodium arsenite, and 17 among 24 clones injected with Rb-86. The use of tracers indicated that largetooth aspen clones of sucker origin each consist of a number of interconnected stem groups. These groups may vary in size from 2 to 10 stems, with the average being 3. The number of stems per group decreased slightly with age, but there was no evidence for decay of parent root connections among healthy trees. The increase in percentage of receptor stems in older stands suggested that interconnected groups had a greater survival capacity than independent aspen trees. Stem to stem transfer of needed materials may contribute to this capacity. Tracer transport implied that translocation of materials may occur among stems under natural conditions. Survival and growth of root pruned, stem girdled, and defoliated largetooth aspen trees were used as criteria for the physiological importance of the parent root system for sucker stems from 3 to 25 years old. Removal of both ends of the parent root significantly reduced growth and was frequently fatal to the treated tree. The few roots that originate from the base of these young suckers were also found to influence growth. Defoliating and girdling allowed a comparison of growth resulting from stored foods with that from currently sysnthesized foods. Leaf areas and leaf weights of aspen suckers were also determined as part of this experiment.