The Effect of Temperature on the Root Growth of Coniferous Seedlings
The purpose of this study was to determine the effect of temperature on the root growth of eight principal coniferous tree species prevalent in the western United States--Pseudotsuga menziesii, Pinus ponderosa, Pinus contorts, Picea engelmanni, Pinus edulis, Picea pungens, Abies lasiocarpa, and Abies concolor. Each year billions of seeds fall from these trees, providing ample opportunity for the establishment of dense young stands of seedlings, yet only a small fraction of the seeds become established as plants. What factors then are involved in the establishment and elimination of tree seedlings? Many, perhaps even most, of the seeds never have a chance to germinate. The reasons for failure are numerous and include considerable loss from rodents, insects, and disease. Some seeds are not viable to begin with. Moisture, in optimum concentration, is a beneficial factor which promotes germination. A prolonged period without water, however, will cause seeds to lose their viability. On the other hand, an excessive amount of water may encourage the growth of fungi, some types of which are capable of destroying seeds. In spite of the above handicaps many seeds manage to germinate, but a number of factors influence the growth of new plants, some causing heavy mortality. A small proportion of the plants originating from germinated seeds survives to become mature trees. First emerging from the seed after germination is the radicle, or root. This embryonic component emerges from an insulated environment within the seedcoat to face various environmental conditions which prevail in the microclimate where the seed has fallen. Barring destruction from natural catastrophe or from fungal attack, each seedling's further development is dependent upon the effect of several environmental factors. In order for the seedling to survive, the factors must react favorably upon the newly exposed radicle; for unless the seed has fallen directly on mineral soil the radicle must reach down into the soil. This exposure to the air accounts for considerable mortality, and unless the seed has a cover of some type, it probably will not even geminate. Since a comprehensive study of all environmental factors and their effect on growth would have been much too exhaustive for this project, the study of only one factor and its effect on one plant part was undertaken. More specifically, this study attempted to isolate some effects of temperature on root elongation and root penetration in the soil. Other findings which were useful in the interpretation of the results were included. The basic data received from the experiment were from the scientific than the practical point of view. Possibly the greatest value was experience gained in working under controlled conditions and in the development of techniques. In spite of the type of data which was gathered, however, several discoveries were made concerning both plant reaction to temperature and plant growth in general which helped to explain some ecological phenomena. The need for experimentation in this field is evident when one reads the recently published textbook on tree physiology by Kramer and Koslowski (1960). Nearly all of the 14 pages devoted to temperature and growth discussed the various plant injuries caused by temperature. Little information was offered concerning temperature and growth rates, especially with conifers. That, of course, was no fault of the authors but merely served to emphasize the need for research in this area.
Owen, Thomas J. (1962). The effect of temperature on the root growth of coniferous seedlings. MS. 131p.