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Knowledge of post-dispersal seed fates and other regeneration characteristics is crucial for predicting abundances and distributions of populations and, ultimately, community species composition and diversity. Seed fate studies, however, are rare primarily due to the difficulty of determining seed fates and causes of mortality. This thesis investigated post-dispersal seed fates for four species common to western Oregon native prairies: Bromus carinatus Hook and Am. var. carinatus, Cynosurus echinatus L., Daucus carota L., and Prunella vulgaris var. lanceolata (Barton) Fern. The general approach was to sow seeds of these species into experimentally manipulated field plots for each of two years, and to recover these seeds from the soil one year later to determine their fates (persistence, death, or establishment as seedlings). The effect of mowing on seedling establishment was also addressed. Additional studies focused on the effects of a single mortality factor, fungal disease, on seed and seedling deaths. The fate of most seeds was death (44%-80%). Few seeds established as seedlings (4%-17%), and mowing did not significantly increase seedling establishment. Only Daucus carota formed a persistent seed bank. Fungal disease generally caused less than 10% mortality. Pot studies corroborated these field results. Other investigators have suggested higher levels of disease in natural vegetation. Vertebrate predation significantly reduced seed numbers for only Bromus carinatus (21%). The largest cause of death for all species for both years was the combined group of other mortality causes (invertebrate predation, interference, and abiotic factors) (52%-73%). The components of this combined group, however, differed among species. The most likely components for Bromus carinatus and Cynosurus echinatus were interference (competition plus allelopathy) and abiotic factors, although invertebrate predation cannot be ruled out for Bromus carinatus. Seedling death due to abiotic factors was most likely the largest component for Daucus carota. The most probable components for Prunella vulgaris were invertebrate predation and abiotic factors. Implications of these findings for population patterns and for restoration of native prairies are discussed. / Graduation date: 1996

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Germination and establishment was evaluated in Arizona cottontop (Digitaria californica (Benth.) Chase), bush muhly (Muhlenbergia porteri Scribn.) and plains lovegrass (Eragrostis intermedia Hitchc.) from southern Arizona. Germination was determined in different aged seed harvested from native and irrigated plots of various populations. Results indicated variability in germination characteristics of study species that appeared unrelated to afterripening or dormancy. Germination ranged from 62 to 96% for Arizona cottontop, 34 to 99% for plains lovegrass, and 75 to 99% for bush muhly. Bush muhly had highest average velocity of germination (58.0 ± 4.1), followed by plains lovegrass (35.9 ± 1.91), and Arizona cottontop (31.4 ± 1.13). Effects of 3 surface treatments (furrows, gravel, litter) and 2 cultivation treatments on establishment of study species and yellow bluestem (Bothriochloa ischaemum (L.) Keng var. ischaemum) was investigated in the field. Bush muhly did not emerge and plains lovegrass had minimal emergence. Arizona cottontop had similar emergence in cultivated and uncultivated plots whereas yellow bluestem had greater emergence in cultivated plots. Litter promoted greater survival of Arizona cottontop. Lower survival in furrows may have resulted from fewer days with available soil moisture and interference from greater density of non-seeded species. Soil covers appear to positively influence survival rather than emergence. Effect of rainfall distribution on germination was investigated using 2 seed retrieval methods. Arizona cottontop and bush muhly germinated after at least 3 days of available soil moisture. Plains lovegrass seeds did not germinate in the field but retrieved seeds had 83% germination, possibly due to light exposure under laboratory conditions. Another study determined whether species have different density and cover under overstory species compared to open areas. Arizona cottontop had either greater, less, or no differences in density under canopied versus open areas. Cover of Arizona cottontop was greater or similar among canopied and open areas. Plains lovegrass had lower or similar density and cover under canopies than in open areas. Bush muhly had greater density and cover under canopies. Overall, studies suggested that species are easily germinated, but accept relatively narrow ranges of environmental conditions for establishment. Establishment may be enhanced by sowing species when rainfall is consistent, extending available moisture through use of soil covers, or mimicking microsites where a species occurs naturally.

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Managing cattle to disseminate seeds of desirable plants, or alternatively, to restrict weed seed contamination on rangelands is of interest to managers. Four experiments were conducted to determine effects of ruminant digestion on germination of ingested seeds. A number of plant species representing a variety of seed size and seed coat hardness were subjected to in vitro digestion. Experiment one was conducted to determine effect of varying lengths of digestion time on seed germination. Seed germination varied by plant species in response to length of digestion. Germination of large soft-coated seeds, such as bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith Goldar) and basin wildrye (Elymus cinereus Scribn & Merril Magnar), was reduced to 0%. Smaller grass seeds, such as Sherman big bluegrass (Poa secunda Presl. Sherman), survived but germination declined following 24-hour, 48-hour, and 72-hour digestion. Experiment two examined effect of different stages of ruminant digestion on seed germination. The combination of Stage I (rumen-simulated digestion) and Stage II (abomasal-simulated digestion) resulted in greatest seed mortality. Two water treatments were included to evaluate the effects of high temperatures (39��C), moisture uptake, and lack of oxygen. Water + O��� and Water + CO��� reduced germination, however not as much as Stage I and Stage II treatments. The third experiment determined effects of diet quality on seed germination. Seeds digested in rumen fluid collected from steers fed a 72% corn concentrate diet resulted in 0% germination for all species. Grass seed germination was low for seeds digested in rumen fluid collected from steers fed a forage diet. Whitetop (Cardaria draba (L.) Hand.) germination was 24% and 28% for 35-hour and 59-hour roughage treatment, respectively, and germination was 0% for 35-hour and 59-hour concentrate treatments. Germination of water-only treatments for most species was reduced in comparison to the control treatment, but was greater than remaining treatments. Experiment four evaluated germination of seeds exposed to in situ versus in vitro digestion. In situ digestion resulted in lower seed germination than in vitro digestion for all species examined. Large, soft grass seeds may not be suitable candidates for reseeding rangelands. However, it is important for managers to recognize that cattle may distribute viable weed seeds in feces. Confining cattle or supplementing with high concentrate diets may help prevent spread of weedy species. / Graduation date: 1997

Seeds of wild rice (Zizania palustris var. interior) have been reported to show highest survival when dehydrated at 25 QC. It has also been reported that axis cells sustained least damage at this drying temperature. In the present study, a linear relationship between drying rate and dehydration temperature was established. Whereas highest positive tetrazolium staining and lowest leakage were recorded for seeds that were dehydrated at 25 QC, maximum germination was recorded for seeds dried at 20 QC. A proportion of seeds showed the presence of glasses, irrespective of the dehydration temperatures used. Parameters of the glass to liquid transition, however, correlated with neither water content nor sugar profiles. The ratio of raffinose to sucrose was similar among all the treatments. A hydroperoxide test revealed a linear relationship between peroxide levels and temperature of drying although the levels of fatty acids were not correlated with hydroperoxide levels. Butanal levels and total aldehydes evolved, on the other hand, showed a high negative correlation with peroxide levels. Electron microscopy showed that the variability and relative abundance of peripheral membrane complexes (PMCs) was the highest for cells of embryonic axes dehydrated at 25 QC and the lowest for embryonic axes of seeds dried at 10 QC. Furthermore, intramembrane particles (IMPs) were evenly distributed in cells of axes dried at 25 or 37 QC. In contrast, membranes of cells of axes dehydrated at 10 QC showed large IMP-free areas. The relative abundance of IMPs was the highest for cells of embryonic axes dried at 25 QC, and the lowest for cells of axes dehydrated at 10 QC. From these observations, it is suggested that membrane phase transition, with the concomitant elimination of proteins, accompanies dehydration of Z. paluslris seeds at 10 QC, whereas at 37 QC peroxidation may predominate. / Thesis (M.Sc.)-University of Natal, Durban, 1996.