The objective of this study was to investigate relationships between seed size, time of germination, and seedling growth in winterfat (Cerutoides lanata (Pursh) J. T. Howell) and silver sagebrush (Artenzisia cuna Pursh). Individual seeds of winterfat were placed into 6 weight classes ranging from 1.5-2.0 to Z-4.0 mg seed-l while silver sagebrush seeds were separated into 7 classes ranging from 0.53 to 0.83 mg seed-l. Seeds were incubated at U°C, seedlings with radicles < 3.0 mm were removed at 1, 2,3, 4-5 and 6-12 day intervals, grown 5 days in darkness at 18oC, and axial length measured. Total germination of winterfat increased 5.5% mg-l increase in seed weight, but germination rate was similar among weight classes, averaging 53.1% day-l. Seed weight and time of germination interactively influenced growth of winterfat seedlings. Seedling length of winterfat was more than 2-fold greater in the > 4.0 than the 1.5-2.0 mg seed-l class while lengths of seedlings in the > 2.0-2.5 through > 3.5 to 4.0 mg seed-l weight classes were intermediate. Seedling length decreased 0.9 to 3.3 mm for each day that germination was delayed from 1 to 12 days with the least and greatest reductions occurring for lightest and medium weight seeds, respectively. Total germination for silver sagebrush initially increased with seed Fight, but declined at weights greater than about 0.57 mg seed-; germination rate was similar (57.1% day-l) among weight classes. Seedling length of silver sagebrush increased 0.3 mm mg-l increase in seed weight whereas length decreased curvilinearly as time to germination was delayed. When winterfat is used for restoration, relatively heavy seeds should be used because they have the greatest germination and produce large seedlings. Because seedling length of silver sagebrush increased with increasing seed weight it is also desirable to select heavier seeds; however, reduced germination in heavier seeds may necessitate increasing seeding rates.
Tolerance to freezing temperatures may be an important factor in the regeneration ecology of winterfat (Ceratoides hata (Pursh) J.T. Howell). Therefore, growth and freezing tolerance of winterfat seedlings were determined after being grown under different controlled temperatures for 7, 14,21, or 28 days. Growth of seedlings was greater under day temperatures of 15 and 20°C relative to 5 and 10°C. Freezing tolerance of seedlings was dependent on seedling age and growth conditions. Younger seedlings were more freezing tolerant than older ones grown under the same environmental conditions. Seedlings grown under lower temperatures were more freezing tolerant than those grown under higher temperatures. The lowest observed lethal temperature for 50% mortality (LT,,) was -ll.V'C for 7-day old seedlings grown under lO/OOC alternating temperatures, and the highest LT50 was about -S'C for seedlings 28 days of age when grown under 29/1"C. Based on seedbed temperatures in the field, the results suggest that freezing temperatures may indeed limit the establishment of winterfat seedlings on Northern Mixed Prairie. Seedbeds with litter accumulations or standing dead plant material may ameliorate low temperature extremes and reduce mortality of winterfat seedlings.
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(Munay et al. 1980). Whether dormant wild oat seeds will respond to the alkaline solutions is unknown, to the best of our knowledge.
Winterfat [Krascheninnikovia lanata (Gueldenstaedt) syn. Ceratoides lanata (Pursh) J.T. Howell, syn. Eurotia lanata (Pursh) Moq.] is a native shrub of mixed prairie of North America. A large portion of hydrated seeds and seedlings can be killed when exposed to seedbed desiccation. Winterfat seeds and young seedlings subjected to varying levels of desiccation were studied to measure the influence of this stress. Germination was unaffected (P>0.05) when seeds were exposed for 0 to 10 hydration-desiccation cycles (2 hours hydration and 22 hours desiccation cycle-1 at 20 to 30% relative humidity and 20°C). Linear increases in germination rate (0.6% day-1 hydration-desiccation cycle-1), seedling length (0.1 mm hydration-desiccation cycle-1), and seed decay (1.5% hydration-desiccation cycle-1) occurred with an increasing number of hydration-desiccation cycles. Seedling survival following desiccation decreased 10.4% mm-1 as seedling length increased from <2mm to 10-15 mm. Seedling survival was positively correlated with relative humidity and negatively correlated with duration of desiccation. The difference (P<0.05) in survival between 0 and 90% relative humidity was 62% for seedlings 4-6-mm in length and 70% for seedlings 9-11-mm in length. Seedlings from seeds that germinated rapidly were more tolerant of desiccation than those from seeds germinating slowly. After desiccation in 30% relative humidity, survival of seedlings from seeds germinating on the first day of incubation was 40% greater than those from seeds germinating on the third day of incubation. Electrolyte leakage indicated that desiccation damaged cells. Establishment of winterfat seedlings will be favored by seedbed conditions that protect seedlings from severe and prolonged desiccation and allow fast entry of the radicle into soil.
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