To summarize, the results of this experiment indicated that the water extract of 

 green needles, roots, duff, and bark of ponderosa pine might contain growth inhibitors. 

 Closer observation, however, indicates that the inhibition of radicle growth by the 

 green needle extracts may have been the combined effects of inhibitor, osmotic poten- 

 tial, and fungal activity. The reduced germination caused by the green needles was most 

 likely the work of the inhibitor alone. Throughfall, which is a natural leachate of 

 pine needles, had no effect on the germination or radicle growth of the pine seeds. 

 Therefore these results do not support the presence of a strong inhibitor, but they do 

 not completely eliminate the presence of a weak toxin that may occur in low concentra- 

 tions in the leachate and accumulates on or in the soil. The water extract of roots 

 reduced germination only slightly, but consistently reduced radicle growth rates. Al- 

 though the root extracts were inhibitory, they did not severely damage the growing 

 ability of the pine radicles. The duff extracts were marginally toxic because the 5 

 and 10 percent solutions were inhibitory to germination in experiment B; also the 10 

 percent solution reduced radicle growth in experiment B. Germination reduction by 

 bark and stemflow was minimal. 



It can be concluded from this experiment that the green needles and roots of 

 ponderosa pine are the most likely tissues containing phytotoxins that interfere with 

 the germination and growth of ponderosa pine seedlings. Bark and duff may contain a 

 weak toxin, but it is probably not significant unless it accumulates in the soil. 



Toxicity of Plant Leachates on Soils 



Materials and Methods 



This experiment was conducted twice, experiment A in the summer of 1974 and experi- 

 ment B in the summer of 1975. There were some technical differences in the setup of 

 each, so the two experimental designs will be discussed separately. 



In experiment A, large samples of green needles, bark, litter, and decomposing 

 duff were collected at the field site and returned to the laboratory. Each plant mate- 

 rial was separately placed on a plastic- lined trough and sprayed with a fine mist of 

 distilled water on a ratio of 1 part plant material to 4 parts of water. The leachate 

 was collected and filtered through paper, approximately one-third was stored in a cold 

 room at 1° to 4°C, and the remaining two-thirds was frozen until needed. 



Soil was collected in large openings away from pine tree influence at the game 

 range. These soils were passed through a 2.0 mm sieve, mixed thoroughly, and then 

 placed into 4-inch plastic pots. Ten replicates were set up for each leachate and a 

 distilled water control. Fifteen stratified and sterilized ponderosa pine seeds were 

 added to each pot. The ten treatment replicates were each watered with 75 ml of their 

 corresponding leachate or distilled water in the case of the control. The treatments 

 were then randomly placed in the greenhouse. The pots were watered when needed with 

 25 ml of the corresponding solution. Germination was checked every day for 15 days, 

 then all seedlings were allowed to grow an additional 10 days at which time all but the 

 largest three seedlings were removed. The remaining three seedlings were allowed an 

 additional 1 month growing period at which time the seedlings were harvested, ovendried 

 at 70°C for 48 hours, and weighed. 



In experiment B the same four plant materials were collected and prepared as in 

 experiment A. In addition to the distilled water control, a Hoagland's solution was 

 included in the list of test solutions. This treatment was added as a nutrient-enriched 

 control for comparison with pine leachates that might have contained higher quantities 

 of nutrients than the distilled water. 



It had been observed in experiment A that the roots of the 2-month-old seedlings 

 were coiled around the bottom of the 4-inch pots. In order to eliminate physical 



10 



