University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln
The Prairie Naturalist Great Plains Natural Science Society
6-2012
Germination Response of Prairie Dropseed and Hairy Goldaster to Stratification and emperT ature
Aurora R. Roemmich
Jack L. Bulter
Gary E. Larson
E. Brent Turnipseed
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This Article is brought to you for free and open access by the Great Plains Natural Science Society at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in The Prairie Naturalist by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. The Prairie Naturalist 44(1):30–38; 2012
Germination Response of Prairie Dropseed and Hairy Goldaster to Stratification and Temperature
1 2 AURORA R. ROEMMICH , JACK L. BUTLER , GARY E. LARSON, AND E. BRENT TURNIPSEED
Department of Natural Resource Management, South Dakota State University, Brookings, SD 57007, USA (ARR, GEL) United States Forest Service, Rocky Mountain Research Station, Forest and Grassland Research Laboratory, 8221 S. Highway 16, Rapid City, SD 57702, USA (JLB) Seed Testing Laboratory, South Dakota State University, Bookings, SD 57007, USA (EBT)
ABSTRACT The unique vegetation assemblage of the Black Hills in conjunction with the frequent occurrence of natural and anthropogenic disturbances emphasizes the need to use locally adapted native species in a wide variety of restoration efforts. However, a general lack of information regarding germination and propagation requirements for most native plant species has restricted their usage. A better understanding of dormancy and germination patterns for native species will increase their availability and affordability. We selected two common native species, hairy goldaster (Heterotheca villosa) and prairie dropseed (Sporobolus heterolepis), to determine their optimum germination conditions. We hand harvested seeds during 2007–2009 for use in germination trials following two pre-treatment conditions (2-week stratification at 5° C and no stratification), under seven temperature treatments in 2009. We used tetrazolium (2, 3, 5-triphenyl-2H-tetrazolium chloride) to determine germination potential of ungerminated seeds. Recognizing significant treatment interactions for both species, percent germination of hairy goldaster seeds was greatest under cooler constant temperatures (15° C or 20° C) with no stratification. Germination of prairie dropseed seeds was significantly influenced by the year in which seeds were collected, which also determined how the seeds responded to stratification. For both species, stratification significantly increased germination of at least one extreme of the temperature gradient (15° C or 30° C). Patterns of germination observed for both are consistent for species inhabiting grasslands and meadows with a fluctuating environment and subjected to moderate seasonal disturbances.
KEY WORDS Black Hills, germination, Hairy goldaster, Prairie dropseed, stratification treatment, temperature treatment
The Black Hills of South Dakota is an intensively native, perennial grass that is widely distributed throughout managed area and has been for more than a century (Ball the United States and Canada, especially in the Great Plains and Schaefer 2000). Most management activities in the where it is considered characteristic of a variety of tall- and Black Hills National Forest are primarily concerned with mixed-grass plant communities (NatureServe 2011). In the timber production (Ball and Schaefer 2000); however, Black Hills, it is an indicator species for the high elevation, management plans also include consideration for wildlife endemic montane grasslands that are currently listed as habitat, rangeland improvement, fire fuels reduction, globally- and state-imperiled (G1S1) by the Natural recreation activities, and control of pests, disease, and Heritage Network and The Nature Conservancy (Marriott et invasive species (Shepperd and Battaglia 2002). Such al. 1999, NatureServe 2011). The seeds of prairie dropseed management activities can profoundly impact plant are relatively large; however, we found no published communities in the Black Hills. In a recent vegetation documentation of seed herbivory. This species also was survey, Marriott et al. (1999) found that 28 of 68 classified used in landscaping as a native ornamental (Springer 2001). plant communities in the Black Hills were considered Hairy goldaster is a perennial forb of the Asteraceae that globally rare (G1–G3). The unique vegetation assemblage is distributed throughout the United States from Michigan to in conjunction with the frequent occurrence of natural and the West Coast and from North Dakota to Texas (United anthropogenic disturbances in the Black Hills emphasizes States Department of Agriculture 2009). Although it is the need for locally adapted species that can be used in a predominantly found in the western United States, its native wide variety of restoration efforts. However, a general lack range also includes portions of Canada. It is widely used as of information regarding germination and propagation an ornamental and has been listed as a forage species for requirements for most native plant species has inhibited bighorn sheep in Nebraska (Vardiman 2010). their availability and usage. Guidelines governing the germination requirements of We selected prairie dropseed (Sporobolus heterolepis) prairie dropseed and hairy goldaster have yet to be and hairy goldaster (Heterotheca villosa) for this study established. For many plant species, especially native because of their widespread distribution throughout a wide species, cold-moist stratification and alternating temperature variety of plant communities in the Black Hills (Larson and regimes often enhance seed germination. Temperature Johnson 1999). Prairie dropseed is a warm-season, tufted, requirements for dormancy-breaking and germination
1 Present Address: Wayne National Forest, Ironton Ranger District, 6518 State Route 93, Pedro, OH 45659, USA 2 Corresponding author email address: [email protected] 31 The Prairie Naturalist · 44(1): June 2012
initiation can provide an indication of the intrinsic species selected for this study were reported among several environmental conditions from which a seed was derived, of the 68 plant associations described by Marriot et al. yet identifying and satisfying those conditions has proven (1999). Four of the 28 globally rare plant associations challenging for many seed researchers. Our objectives were found in the Black Hills contained at least one of the to use hand-collected seeds from diverse, wild populations species. Prairie dropseed was recorded among seven total in the Black Hills to 1) evaluate germination under different plant associations, three of which were considered rare. temperature regimes, 2) examine the effects of cold-moist Hairy goldaster was found among 11 total plant stratification on the response of seed germination to associations, three of them rare. temperature, and 3) evaluate the year to year variation in germination. Such information is important in identifying METHODS the optimal environmental conditions to overcome dormancy and induce germination with the ultimate goal of We hand-collected seeds for this study from 7 sites increasing the availability, usability, and affordability of located within the central to west-central portions of the these species for restoration projects and promoting the use Black Hills during the summers of 2007–2009 from mid- of locally adapted native species in landscaping. August through mid-September when the seed units were mature and ready to be shed. For hairy goldaster, we STUDY AREA collected seeds when the pappus on the achenes was evident, while prairie dropseed seeds were collected when The Black Hills comprised an unglaciated, mountainous the florets began disarticulating from the spikelets. The uplift that spanned approximately 200 km north to south and distance between collection sites ranged from 5 km to 39 100 km east to west, covering an area of about 15,540 km2 km (average distance = 21 km, SD = 9.2) based on 21 (Froiland 1990). Elevation ranged from 914 m in low-lying straight-line measurements between sites. Each collection areas to 2,208 m at the highest point (Harney Peak). The year represented a ‘seed lot’ (i.e. 2007 seed lot, 2008 seed climate of the Black Hills and surrounding Northern Great lot, and 2009 seed lot). Cleaned seeds were stored dry at – Plains was representative of the temperate steppe, which 12° C to maintain viability (Walters et al. 2005). In January was characterized by cold winters and hot summers (Bailey 2009, we randomly selected filled seeds for evaluating et al. 1994). Average annual precipitation in the Black Hills initial viability prior to the germination trials. from 1971–2000 ranged from 51 cm in the southern region We tested the initial viability of collected seeds using to 76 cm in the northern region. The temperature standardized tetralozium (TZ) tests (Peters 2000). Two minimum/maximum in the northern Black Hills (Lead, SD) hundred randomly selected seeds of each species were first averaged –10° C/0° C in January and 13° C/25° C in July; imbibed with distilled water and soaked for 4 hours (hairy while the minimum/maximum in the southern region goldaster) or 12 hours (prairie dropseed) in a 1.0% (Custer, SD) averaged –11° C/2° C in January and 11° concentration of 2, 3, 5-triphenyl-2H-tetrazolium chloride C/27° C in July (South Dakota Office of Climatology 2010). solution. Hydrogen ions, produced by cellular respiration of Length of the growing season varied by elevation and living tissue, combined with Tetrazolium to form an latitude but typically comprised 100–154 days between May insoluble red formazan dye (Cottrell 1947, Lambou 1953, and September (Heyward 1928, Shepperd and Battaglia Baskin and Baskin 1998). The result was a red stain of 2002). living tissue that indicated viability in both dormant and Vegetation of the Black Hills was a culmination of non-dormant seeds (Baskin and Baskin 1998). species overlap from Cordilleran Forest, Grassland, Eastern After the initial viability was determined, we conducted Deciduous Forest and Northern Coniferous Forest biomes germination trials for each seed lot under two pre-treatment (Marriott et al. 1999). Vegetation classifications of the conditions (stratified and non-stratified) and seven Black Hills tended to center around Ponderosa pine (Pinus temperature treatments. We applied the stratification ponderosa) because of its role as a dominant species that treatment for two weeks on three layers of moistened blotter was only absent from areas that were characteristically paper at 5° C. Baskin and Baskin (1998) point out that there treeless (Hoffman and Alexander 1987). Hoffman and are few studies that investigate the optimal cold Alexander’s (1987) habitat type classification recognized stratification interval for temperate grassland species; eight habitat types for ponderosa pine and included however, of the available studies, the requisite period additional habitat classifications for areas dominated by bur appeared to be brief. Additionally, Totterdell and Roberts oak (Quercus macrocarpa), quaking aspen (Populus (1979) and Bouwmeester and Karssen (1992) found that tremuloides), and Black Hills spruce (Picea glauca). Plant dormancy can be re-induced through extended stratification community classification by Marriott et al. (1999) followed periods. the U.S. National Vegetation Classification System which We placed 50 randomly selected filled seeds from each resulted in 68 plant associations for the Black Hills area; collection year in 12-cm 12-cm plastic germination boxes fifteen of the 68 were dominated by ponderosa pine. Both on double-layer blotter paper. We randomly assigned each
Roemmich et al. · Germination of Two Black Hills, SD Species 32
germination box (our experimental unit) to a stratification For hairy goldaster, the most dramatic response to and temperature treatment combination and each treatment temperature occurred at the highest constant temperature combination (seed lot, stratification, and temperature) was treatment (30º C; Fig. 1a). Excluding the constant 30º C replicated 8 times. We transferred the germination boxes to temperature treatment, germination under the remaining one of the seven temperature treatments that consisted of temperature treatments ranged from 71% to 89% for the three alternating temperature settings (15/25° C, 15/30° C, 2007 seed lot ( = 83%), 71% to 82% for the 2008 seed lot and 20/30° C) and four constant temperatures (15° C, 20° C, ( = 80%), and 85% to 95% for the 2009 seed lot ( = 25° C, and 30° C) controlled within ± 1° C. During one 24- 89%). The effect of stratification on germination depended hour period, each of the temperature treatments was upon seed lot and temperature (Fig. 1b). Excluding the provided 8 hrs of light and 16 hrs of darkness. The constant 30º C temperature treatment, germination of alternating temperature cycles incorporated the light period stratified seeds was either a) similar to their non-stratified during the highest temperature interval. We conducted counterparts (P > 0.05), b) slightly but significantly higher germination counts at 28 days, at which time we terminated (15/30º C temperature for the 2008 seed lot, (t1,294 = 4.98, P the germination experiment. We evaluated prairie dropseed < 0.001), c) or significantly lower (P < 0.001), especially for germination based on the presence of an elongated seeds collected in 2007. Germination of stratified seeds coleoptile with enclosed leaves, an attached endosperm, and exposed to the 30º C temperature treatment was 150% an elongated primary root. Seed germination for hairy (2007), 184% (2008), and 46% (2009) greater than non- goldaster was based on the presence of an elongated primary stratified seeds collected the same year and under the same root and secondary root structures, an elongated hypocotyl, temperature treatment. Final germination following and photosynthetically active cotyledons. All of these stratification was similar (P > 0.05) among seed lots and seedling characteristics indicate the ability to produce and temperature treatments, including the 30º C temperature sustain a functional plant (Association of Official Seed (Fig. 1b). Analysts 2007). At the conclusion of the germination trials, Germination of prairie dropseed seeds was largely we tested the viability of ungerminated seeds using influenced by seed lot (Table 1, Fig. 2). Germination of standardized tetralozium (TZ) tests as described above. non-stratified seeds (Fig. 2a) collected in 2007 and 2008 We calculated dormancy by dividing the number of was, with the exception of the 15º C temperature (t1,294 = ungerminated viable seeds, detected using the TZ test, after 6.60, P < 0.001), similar (P > 0.05) among the temperature 28 days by the total number of ungerminated seeds. treatments and ranged from 21% to 42% (average = 28%), Because of the non-random nature of the dormancy data, while percent germination of seeds collected in 2009 ranged only descriptive statistics (mean ± 95% confidence from 39% to 81% (average = 61%). Germination of non- intervals) were calculated. We analyzed the effects of stratified seeds collected in 2009 averaged 154% and 97% temperature, stratification, and seed lot (2007, 2008, and higher than seeds collected in 2007 and 2008, respectively. 2009), and their interactions on final germination counts (28 The effect of temperature on germination was observed days) using a fixed-effects, generalized linear model for mainly in the 2009 seed lot. binomially distributed data with the logit link function (SAS Collection year had a major effect on how prairie Version 9.2; SAS Institute 2008). We separated means dropseed seeds responded to the stratification treatment using the LS means procedure with a Tukey adjustment to (Fig. 2b). Mean germination of stratified seeds collected in control the experimentwise error rate. For ease of 2007 was similar (P > 0.05) to non-stratified seeds across presentation, we separated means among temperature the majority of the temperature treatments, with the 15/25º treatments within each stratification treatment (stratified and C temperature treatment serving as the exception (t1,294 = non-stratified), then across stratification (stratified vs. non- 4.14, P = 0.03). In contrast, mean germination of stratified stratified) within individual temperature treatments. seeds collected in 2008 was 40% to 100% higher (P < 0.05) than their non-stratified counterparts. While germination of RESULTS non-stratified seeds was similar (P > 0.05) between the 2007 and 2008 seed lots, stratification increased germination of Initial seed viability tests on hairy goldaster seeds that the 2008 seed lot compared to the 2007 seed lot at all but the were soaked for 4 hours in TZ solution indicated viability 15º C temperature. There was no effect (P > 0.05) of levels (e.g., potential germinability) of 79%, 91%, and 65% temperature on germination of stratified seeds collected in for the 2007, 2008, and 2009 seed lots, respectively. Initial 2009, again with the exception of the 15º C temperature, TZ tests of the 2007, 2008, and 2009 seed lots for prairie however, stratification increased germination at all but the dropseed seeds revealed viability levels of 74%, 99%, and 15º and 20º C temperatures. Average germination of 93%, respectively. stratified seeds collected in 2009 was 175% and 100% Germination at the end of the experiment was greater than stratified seeds collected in 2007, and 2008, significantly influenced by the interaction of temperature, respectively, similar to the trend observed in comparison of stratification, and collection year for both species (Table 1). non-stratified seeds among seed lots.
33 The Prairie Naturalist · 44(1): June 2012
Because of the high germination percentages of hairy day germination trial and most were concentrated at the goldaster seeds, especially at the lower temperatures, there lower temperatures (Fig. 3b). A similar but more were few ungerminated seeds after 28 days available to pronounced pattern was observed for the 2008 and 2009 evaluate dormancy. Although variable, about 20% of the seed lots. Approximately 50% of the ungerminated seeds ungerminated seeds were recorded as dormant, and nearly from the 2008 seed lot under the 15º C temperature were all of those were observed at the higher temperatures (Fig. viable, while 75% to 90% of 2009 seed lot under the same 3a). In contrast, overall germination of prairie dropseed temperature were viable, regardless of stratification seeds was low compared to hairy goldaster seeds. There treatment. were few viable seeds in the 2007 seed lot following the 28-
Table 1. Results of the generalized linear model evaluating the effects of temperature (Temp), stratification (Strat), and year of collection (Seed Lot), and their interactions on mean germination percentages for hairy goldaster and prairie dropseed (denominator df = 294) in the Black Hills, South Dakota, during 2007–2009.
Hairy goldaster Prairie dropseed
Effect df F-value P > F F-value P > F
Temp 6 209.0 < 0.001 46.1 < 0.001
Strat 1 9.1 0.003 234.5 < 0.001
Temp*Strat 6 54.7 < 0.001 3.4 0.003
Seed Lot 2 127.3 < 0.001 1,067.5 < 0.001
Temp*Seed Lot 12 9.1 < 0.001 22.9 < 0.001
Strat*Seed Lot 2 87.9 < 0.001 95.5 < 0.001
Temp*Strat*Seed Lot 12 17.2 < 0.001 5.8 < 0.001
DISCUSSION very least, to the appropriate season (Washitani and Masuda 1990). Often, lower temperature limitations are a reflection Our findings establish baseline patterns of seed of ecological adaption (ecotype) while upper temperature germination for prairie dropseed and hairy goldaster in a limits may result from physiological constraints determined laboratory setting where environmental factors were strictly by the environment experienced by the parent during seed controlled. While dormancy-breaking requirements often maturation (Brändel 2006). are variable and difficult to identify, germination While determining germination responses to temperature requirements for most seeds typically include adequate was complicated by treatment interactions, the overall effect moisture levels, suitable temperatures, and proper lighting of temperature on germination for hairy goldaster seeds was (Bewley 1997, Finch-Savage and Luebner-Metzger 2006). strongest at a constant temperature of 30º C. This In addition, interactions among these factors are not well temperature may define the upper metabolic limits for this known or understood and may be the result of physiological, species with respect to temperature, which appears to be nutritional, metabolic, or mechanical properties (Totterdell ameliorated by stratification. Stratification has been proven and Roberts 1979, Bewley and Black 1982). Nonetheless, to expedite the dormancy breaking process (Davis 1930, temperature is often regarded as the single most important Toole et al. 1955, Baskin and Baskin 1998) and increase the environmental factor because of its role in breaking range of temperatures at which seeds can germinate (Baskin dormancy (Bouwmeester and Karssen 1992, Vleeshouwers and Baskin 1988). In temperate regions of North America, et al. 1995) and determining germination success (Baskin spring and early summer provide environmental conditions and Baskin 1988). While germination was not studied in that are most conducive to seed germination of most the field, it is likely that the most productive temperature species; therefore, it is reasonable to expect that cold-moist treatments for both species would correspond to soil stratification would increase seed germination because it is a temperatures at the time of seedling emergence or, at the simulation of winter conditions. Milberg and Andersson
Roemmich et al. · Germination of Two Black Hills, SD Species 34
(1998) suggested that variation in germination within a seeds exposed to 30º C, which showed higher (P < 0.001) single seed collection event can be moderated by germination percentages following stratification for all seed stratification treatment. This may be the case for stratified lots.
120 a. 2007 2008 2009 a ab a abc 100 ab bc ab ab ab ab b bc bc bc bc 80 c c bc
60 f 40 d d Germination (%) Germination 20 1200 b. wx w wx 100 w w wx wx *w wx x wx xywx x *xy *xy 80 *y *y *yz *z 60 *yz
Germination (%) Germination 40
20
0 15 20 15/25 15/30 20/30 25 30 Temperature (Cº)
Figure 1. Mean percent germination (± SD) of non-stratified (a) and stratified (b) hairy goldaster (Heterotheca villosa) seeds after 28 days in response to temperature treatments. Bars within each graph followed by different letters indicate significant differences (P < 0.05) in mean germination (a-f for non-stratified seeds and w-z for stratified seeds). * in lower graph (b) indicates significant differences (P < 0.05) in germination percentages between stratified and non-stratified seeds within each temperature treatment.
Effects of stratification and temperature on germination minor effect, which suggested more than one optimal responses of hairy goldaster seeds also were influenced by temperature similar to results reported by Larson (2002). the year in which seeds were collected. For example, while With one exception (15º C), germination of non-stratified stratification treatment increased germination of hairy seeds in the 2009 seed lot was greater (P <0.001) compared goldaster seeds under high temperature treatments, to the 2007 and 2008 seed lots. The observed differences in stratification had a variable effect on other temperature germination related to collection year may simply be a treatments and among seed collection years. For the 2007 consequence of the additional time in cold storage for the seed lot, stratification appeared to increase dormancy in 2007 and 2008 seed lots, although we found no weakly dormant seeds under several temperature treatments documentation regarding the longevity of prairie dropseed (Milberg and Andersson 1998). However, significant seeds in cold storage. However, Walters et al. (2005) variation in germination has been shown to exist between reported that following 41.8 years of cold storage at –18º C individual plants within a population and between seed the initial germination of alkali sacaton (Sporobolus collection years that cannot be fully explained by airoides) was only reduced 13% (96% to 84%). environmental conditions (Andersson and Milberg 1998). Alternatively, in our study differences in germination Collection year had a pronounced effect on germination responses among years also could be the result of of prairie dropseed seeds while temperature had a relatively environmental conditions experienced by the parent plant
35 The Prairie Naturalist · 44(1): June 2012
during seed development that influenced the adaptive life Conversely, exposure to low temperatures typically results histories of the offspring, including patterns of germination in a prolonged developmental period that allows the seed (Donohue 2009). Temperature, nutrient, moisture and light coat to further develop, which leads to greater seed availability, light quality, and position held by the seed dormancy (Allen and Meyer 2002, Lacey 1996, Lacey et al. within the inflorescence or the age of the maternal plant at 1997). Seeds for the two species used in our study were the time of embryogenesis have been shown to impact seed collected from a variety of populations. Consequently, the dormancy and germination (Gutterman 1992). Extreme influence of environmental variation on maternal effects environmental conditions experienced at the time of seed was difficult to assess because of the high geographic development, such as high temperatures and water-stress, variation in the Black Hills that influenced temperature and often result in low seed dormancy and, subsequently, high precipitation. germination (Allen and Meyer 2002, Figueroa et al. 2010).
120 a. 2007 2008 2009 100 a a 80 b b b 60 d d d cd cd c c 40 c c c c c c c c
Germination (%) Germination 20 e 1200 b. z* z z 100 z* z* z* 80 x 60 x* x* x* x* x* xy* y y* y y y y 40 y* y
Germination (%) Germination 20 0 15 20 15/25 15/30 20/30 25 30 Temperature (Cº) Figure 2. Mean percent germination (± SD) of non-stratified (a) and stratified (b) prairie dropseed (Sporobolus heterolepis) seeds after 28 days in response to temperature treatments. Bars within each graph followed by different letters indicate significant differences (P < 0.05) in mean germination (a-f for non-stratified seeds and x-z for stratified seeds). * in lower graph (b) indicates significant differences (P < 0.05) in germination percentages between stratified and non-stratified seeds within each temperature treatment.
Interacting effects of temperature, stratification, and seed spring and early summer, while soil temperatures stabilize lot may be further complicated by constant or alternating as summer progresses. Likewise, seeds at varying soil temperatures, although we did not statistically evaluate the depths gauge burial depth by the amplitude of temperature differences in germination among constant and alternating fluctuations, which is less at greater soil depths and more temperatures. We included temperature fluctuations in the pronounced at the surface. The presence and extent of experiment because they often signify environmental openings in vegetative cover also are conveyed through changes that are essential for seed germination, such as soil temperature fluctuations because vegetation acts as an depth, seasonality, and niche availability (Grime 1979, insulator that stabilizes ground surface temperatures Baskin and Baskin 1988, Van Assche and Vanlerberghe (Pearson et al. 2002). Overall, we did not observe any 1989). More extreme differences (greater amplitude) in detectable germination responses to alternating temperatures temperature fluctuations naturally signify the arrival of for either species. However, determining effects of
Roemmich et al. · Germination of Two Black Hills, SD Species 36
alternating temperatures often are complicated by at least prior to germination trials. Notable exceptions were the nine related factors that include amplitude, number of stratified and non-stratified seeds exposed to the 30º C cycles, warming rate, cooling rate, higher temperature value, temperature treatments that were collected in 2007 and lower temperature value, length of interval at the higher 2008. In contrast, the percent of dormant seeds at the end of temperature, length of interval at the lower temperature, and the experiment for prairie dropseed appeared to be the timing of cycle(s) after imbibition (Totterdell and influenced by seed lot and temperature, suggesting Roberts 1980). considerable loss of seed viability at the higher Dormancy of all ungerminated seeds was evaluated at the temperatures, there was no obvious effect of stratification. end of the experiment (Fig. 3). The few ungerminated hairy Thus, total live seeds for prairie dropseed were substantially goldaster seeds determined to be dormant were typically less than the initial viability values for the majority of the those seeds under the higher temperatures with no apparent treatment combinations. In this case, the exceptions were trend with respect to stratification or seed lot. In general, seeds collected in 2009 exposed to the lower temperatures the percent of total live seed (germinated plus dormant) was (<15/30º C). equal to or greater than the percent of viable seeds evaluated
100 a. 15 20 15/25 15/30 20/30 25 30 80
60
40
Dormancy (%) Dormancy 20
0 No Strat Strat No Strat Strat No Strat Strat
2007 2008 2009
100 15 20 15/25 15/30 20/30 25 30 b. 80
60
40 Dormancy (%) Dormancy 20
0 No Strat Strat No Strat Strat No Strat Strat
2007 2008 2009
Figure 3. Mean percent dormancy (± 95% confidence limits) of hairy goldaster seeds (Heterotheca villosa; a) and prairie dropseed seeds (Sporobolus heterolepis; b) by year in response to temperature and stratification temperatures. Values were calculated based on the number of ungerminated seeds that tested positive (tetralozium test) relative to the total number of ungerminated seeds.
37 The Prairie Naturalist · 44(1): June 2012
MANAGEMENT IMPLICATIONS Baskin, C. C., and J. M. Baskin. 1998. Seeds: ecology, biogeography, and evolution of dormancy and Results from our study indicate that hairy goldaster seeds germination. Academic Press, San Diego, readily germinate under a variety of temperatures less than California, USA. 30° C. When the species is used for restoration, the most Bewley, J. D. 1997. Seed germination and dormancy. The suitable establishment method may be to cast seed in early Plant Cell 9:1055–1066. spring. We found that prairie dropseed has more than one Bewley, J. D. and M. Black. 1982. Physiology and optimal germination temperature, and that responses to both biochemistry of seeds in relation to germination. 2. temperature and stratification are strongly influenced by Viability, dormancy and environmental control. seed collection year. Collection year variability emphasizes Springer-Verlag, Berlin, Germany. the need to evaluate germinability of different seed lots. Bouwmeester, H. J., and C. M. Karssen. 1992. The dual The best approach for restoration may be to transplant role of temperature in the regulation of the seasonal mature individuals into established vegetation (Howell and changes in dormancy and germination of seeds of Kline 1992, Fedewa and Stewart 2009). Polygonum persicaria L. Oecologia 90:88–94. Brändel, M. 2006. Effects of temperatures on dormancy ACKNOWLEDGMENTS and germination in three species in the Lamiaceae occurring in northern wetlands. Wetlands Ecology We thank D. Hardesty, S. Harrelson, E. Helms, H. and Management 14:11–28. McGranahan, C. Mayer, K. Owens, C. Vetter, and H. Cottrell, H. J. 1947. Tetrazolium salt as a seed germination Wisner for assistance in seed collecting, cleaning, and indicator. Nature 159:748. sorting. Thanks also are given to D. Ruhlman and R. Davis , W. E. 1930. Primary dormancy, after-ripening, and Parmely for their guidance on germination testing. the development of secondary dormancy in Appreciation is extended to S. Baggett for statistical embryos of Ambrosia trifida. American Journal of assistance and M. Haar for reviewing an early draft of the Botany 17:58–76. manuscript. Our manuscript benefited from the comments Donohue, K. 2009. Completing the cycle: maternal effects and suggestions made by two anonymous reviewers. This as the missing link in plant life histories. research was supported in part by funds provided by the Philosophical Transactions of the Royal Society B- Rocky Mountain Research Station, United States Forest Biological Sciences 364:1059–1074. Service, and the United States Department of Agriculture. Fedewa, C. A., and J. R. Stewart. 2009. Seed germination characteristics of prairie dropseed (Sporobolus LITERATURE CITED heterolepis). Natural Areas Journal 29:188–192. Figueroa, R., D. A. Herms, J. Cardina, and D. Doohan. Allen, P. S., and S. E. Meyer. 2002. Ecology and 2010. Maternal environment effects on common ecological genetics of seed dormancy in downy groundsel (Senicio vulgaris) seed dormancy. Weed brome. Weed Science 50:241–247. Science 58:160–166. Andersson, L., and P. Milberg. 1998. Variation in seed Finch-Savage, W. E. and G. Leubner-Metzger. 2006. Seed dormancy among mother plants, populations and dormancy and the control of germination. New years of seed collection. Seed Science Research Phytologist 171:501–523. 8:29–38. Froiland, S. G. 1990. Natural history of the Black Hills and Association of Official Seed Analysts. 2007. Seedling Badlands. The Center for Western Studies, Sioux evaluation handbook. Contribution no. 35 to the Falls, South Dakota, USA. handbook on seed testing. Association of Official Grime, J. P. 1979. Plant strategies and vegetation Seed Analysts, Las Cruces, New Mexico, USA. processes. John Wiley and Sons Ltd, London, UK. Ball J. J., and P. R. Schaefer. 2000. Case no. 1: one Gutterman, Y. 1992. Maternal effects on seeds during hundred years of forest management. Journal of development. Pages 27–59 in M. Fenner, editor. Forestry 98:4–10. Seeds: The ecology of regeneration in plant Bailey, R. G., P. E. Avers, T. King, and W. H. McNab. communities. CAB International, Wallingford, 1994. Ecoregions and subregions of the United UK. States (map). United States Department of Heyward, H.E. 1928. Studies of plants in the Black Hills of Agriculture, Forest Service, Washington, D.C., South Dakota. Botanical Gazette 85:353–412. USA. Hoffman, G. R., and R. R. Alexander. 1987. Forest Baskin, C. C., and J. M. Baskin. 1988. Germination vegetation of the Black Hills National Forest of ecophysiology of herbaceous plant species in a South Dakota and Wyoming: a habitat type temperate region. American Journal of Botany classification. United States Department of 75:286–305. Agriculture, Forest Service, Rocky Mountain
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Forest and Range Experiment Station Resource ponderosa pine. U.S. Department of Agriculture, Publication RM-276, Fort Collins, Colorado, USA. Forest Service, Rocky Mountain Forest and Range Howell, E. A., and V. M. Kline. 1992. The role of Experiment Station General Technical Report competition in the successful establishment of RMRS-GTR-97, Fort Collins, Colorado, USA. selected prairie species. Pages 193–197 in South Dakota Office of Climatology. South Dakota State Proceedings of the Thirteenth North American University, Brookings, South Dakota, USA. Prairie Conference. Ontario, Canada.