It is also possible that weak phytotoxins could have been responsible. The extract 

 experiment revealed potential phytotoxins in green needles, bark, duff, and roots, and 

 the soil leachates experiments failed to eliminate the possibility of weak toxins or 

 breakdown products accumulating on the soil. Therefore, weak toxins in the canopy soil 

 could have reduced the germination. 



Another explanation is an interaction or the combined effects of moisture tension 

 and a weak phytotoxin working synergistically to reduce germination in the canopy soils. 

 The two factors working simultaneously may be more inhibitory than either factor 

 separately. 



The factors influencing germination apparently had no effect on the growth and 

 development of young pine seedlings, since there was no significant difference in total 

 seedling weights, shoot weights, or root weights between treatments in either experiment 

 A or B. There were greater concentrations of nutrients measured in the canopy soils, 

 but the differences were apparently not great enough to affect seedling growth. 



Seedbed Effect on Germination 



Materials and Methods 



The possibility that the germination and growth of ponderosa pine seeds and seed- 

 lings are influenced by the seedbed in which the seeds overwintered was investigated 

 by a field and a laboratory experiment. 



In the field seedbed experiment, seven different seedbeds were prepared at the 

 edge of a small opening at the game range field site on November 20, 1974. Six of the 

 seedbeds were set up in the opening and one under the canopy of several trees bordering 

 the opening. The seedbed beneath the canopy was prepared by scraping away the litter 

 and duff to expose the surface soil. This treatment shall be referred to as the canopy 

 topsoil (canopy). The vegetation and litter were scraped away from six small areas in 

 the opening, and each was covered with one of the following materials: topsoil collected 

 from under a ponderosa pine canopy, referred to as canopy topsoil (opening) ; topsoil 

 from a large opening; subsoil from a large opening; litter; decomposing duff; and de- 

 composing duff with litter on top. A large number of unstratified ponderosa pine seeds 

 were then placed on each of the seven seedbeds. The seeds on the soil seedbeds were 

 not treated further, while those in plant materials were covered with the corresponding 

 plant material. In the duff and litter combined treatment, the pine seeds were placed 

 on top of decomposing duff, and the litter was then placed over the top of the seeds. 

 Small hardware cloth exclosures were placed over each seedbed to ban rodents. 



On May 9, 1975, the seeds were collected and taken to the laboratory where the 

 germination tests were conducted. Sterilized cellulose sponges were soaked in dis- 

 tilled water, drained, and placed in the bottom of 9 cm plastic petri dishes. Each 

 sponge was covered with a wet 7 . cm piece of filter paper. Twenty seeds from each 

 treatment were placed in respective petri dishes. Four replications were set up for 

 each treatment. The petri dishes were covered and randomly placed in a growth chamber 

 set at 25° to 27°C. The germination was checked daily for 1 week. 



For the laboratory experiment, litter, duff, and topsoil from under a ponderosa 

 pine canopy were collected along with topsoil from a nearby opening on November 20, 

 1974. These materials were returned to the laboratory to be used as overwintering 

 seedbeds for ponderosa pine seeds. The litter and duff samples were soaked separately 

 for two hours in distilled water and then transferred to 100 by 80 mm petri dishes. A 

 third seedbed was set up using a combination of duff covered with litter. The opening 

 and canopy soils were placed into petri dishes and brought to saturation with distilled 

 water. The control was silica (sand) brought to saturation. Eight replications were 



15 



