M. Sean Willison, Patricia S. Holloway, Stephen S. SparrowUniversity of Alaska Fairbanks, School of Natural Resources and Agricultural Sciences, Fairbanks, AK

Germination characteristics of wetland sedges from Prudhoe Bay, Alaska

Introduction:With continuing development in the oilfields on the North Slope of Alaska, it is becoming increasingly important to develop successful rehabilitation practices for disturbed sites (e.g. Figure 1). Rehabilitation of disturbed lands in the Arctic is challenged by low temperatures, nutrient availability, and low soil moisture. Land rehabilitation methods include fertilizing adjacent tundra to encourage seed production, sowing of native-grass cultivars and indigenous seeds, and transplanting tundra plugs and sod (Figure 2).

Arctic vegetation is dominated by wetland plant communities. Two of the most common wetland species, Carex aquatilis (Figure 3) and Eriophorum angustifolium (Figure 4), were studied to determine germination characteristics when used in rehabilitation programs. These sedges are known to colonize disturbed sites (e.g. Phillips, 1954; Ebersole, 1985; Jorgenson and Joyce, 1994; Kidd et al., 2006) and, once established, spread via rhizomatous growth (Leck and Schütz, 2005). There are few studies that have provided quantitative results; but, seeds of these sedges have been used by rehabilitation ecologists for a number of years. To address the need for successful rehabilitation methods, this study investigated seed germination under different environmental conditions.

Figure 2. Tundra sod, an example of a land rehabilitation method.

Figure 1. Gravel pad with partial removal of the gravel; an example of a Prudhoe Bay disturbance site.

Figure 3. Mature Carex aquatilis. Figure 4. Mature Eriophorum angustifolium.

Methods:Carex aquatilis and Eriophorum angustifolium seeds were harvestedin 2008 within the Prudhoe Bay oilfield (Figure 5) from 30 individual sites per species (Figure 6). Seeds were harvested three times, at two week intervals, corresponding with maximum seed maturity. Dateranges and morphological characteristics of seed maturity were determined from preliminary investigations conducted during the previous year. Within one week of harvest, filled and empty seeds were mechanically separated (Figure 7) and filled seeds were randomly chosen for testing.

Treatments consisted of four replicate petri dishes, with 100 seeds on moistened filter paper per dish (Figure 8). Seeds were checked for germination for up to 60 days in germination chambers (Figure 9). At the end of each test, all ungerminated seeds were cut open to determine viability; only filled seeds were included in the final analysis.

Analysis of variance was used to test for significance differences for percent germination among different harvest locations (30 sites), different harvest dates (3 dates), constant (25°C) versus alternating (25/10°C, 18 and 6 hours, respectively) temperatures, seed storage methods (fresh, after-ripened, wet-cold stratified, and after-ripened plus cold-wet stratification), and light conditions (total light or total dark).

Figure 5. Location of the Prudhoe Bay Oilfield.

Figure 6. Sedge seeds were harvested and bulked from 30 stands per species.

Figure 7. Forced air was used to separate Eriophorum seeds from plant debris.

Figure 9. Treatments consisted of four replicates, with 100 seeds per replicate.

Figure 8. Seeds were checked for germination for up to 60 days.

Results and Discussion:Significantly more seeds of both sedge species germinated with increased light, fluctuating temperatures (Figure 10), and following cold-wet stratification. These results are in agreement with previous studies (e.g. Baskin and Baskin, 2001; Leck and Schütz, 2005) that indicated these sedge species displayed physiological dormancy controls. However, the percent germination of Carex seeds was considerably higher than Eriophorum seeds. Carex displayed a maximum germination of 75.2% under conditions of 6 month after-ripening at 4°C, followed by sixty days of cold-wet stratification at 4°C, and incubation at 25/10°C (Figure 11). Eriophorum displayed a maximum germination of 10.7% after sixty days of cold-wet stratification at 4°C and incubation at 25/10°C (Figure 11).

Germination of both species varied considerably by harvest location. After-ripened Carex seeds grown under standard light quality ranged from 32.5 to 87.9% germination and fresh Eriophorum seeds ranged between 0.0 and 7.6% germination. These results suggest that in order to avoid using low viability seeds for rehabilitation, these sedge seeds should be collected from multiple sources, bulked together and tested for viability prior to application. Carex germination percentage by collection date did not differ significantly, while collection date was associated with significant differences for Eriophorum (Figure 12), showing that Carex displayed a wider range of harvest dates for achieving maximum germination. In summary, these results suggest that seeding disturbed sites with Carex should be more useful than Eriophorum and may be beneficial for arctic rehabilitation programs.

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Seed collection date7.30.0 8.13.08 8.27.08 9.10.08 9.24.08

Figure 10. Germination percent by temperature treatment.

Figure 12. Germination percent by harvest date treatment.

Conclusion:Germination trials conducted over a range of environmental variables indicate that germination of Carex aquatilis and Eriophorum angustifolium seeds from the Alaskan arctic are subject to physiological dormancy controls. Germination success of both species varied significantly by harvest location, seed storage method, temperature regime, and light condition. Eriophorum germination was also significantly different by harvest date. Overall, germination of Carex seeds was much higher than Eriophorum seeds. These germination results suggest that Carex seeds, collected locally, could be successfully applied in arctic land rehabilitation programs. It is important to note, however, that germination under laboratory conditions would not necessarily mimic environmental conditions in the field. To better understand how Carex seed could be used in rehabilitation programs, future studies should quantify seedling establishment and survival under field conditions with differing substrata and moisture regimes, as well as measuring seedling growth rate over time. Determining whether stand seed quantity and viability differ over time would help land managers and rehabilitation ecologists to set appropriate seed harvest goals and produce a better result.

Figure 11. Germination percent by seed storage method.

Kidd, J.G., Streever, B., and Jorgenson, M.T. 2006. Site characteristics and plant community development following partial gravel removal in an arctic oilfield. Arctic, Antarctic, and Alpine Research. 38(3):384-393.

Leck, M.A., and Schütz, W. 2005. Regeneration of Cyperaceae, with particular reference to seed ecology and seed banks. Perspectives in Plant Ecology, Evolution, and Systematics. 7:95-133.

Phillips, M.E. 1954. Eriophorum angustifolium Roth. Journal of Ecology. 42(2):612:622.

Literature cited:

Baskin, C.C., and Baskin, J.M. 2001. Seeds: Ecology, biogeography, and evolution of dormancy and germination. San Diego, CA. Academic Press. 666 p.

Ebersole, J.J. 1985. Vegetation disturbance and recovery at the Oumalik Oil Well, Arctic Coastal Plain, Alaska. Ph.D. dissertation, University of Colorado, Boulder. 408 p.

Jorgenson, M.T., and Joyce, M.R. 1994. Six strategies for rehabilitating land disturbed by oil development in arctic Alaska. Arctic. 47(4):374-390.

Acknowledgements:

This poster is the result of research sponsored by Alaska Sea Grant with funds from the National Oceanic and Atmospheric Administration Office of Sea Grant, Department of Commerce, BP Exploration Alaska, Inc. and from the University of Alaska with funds appropriated by the state. We thank Bill Streever for initiating this research, Tim Cater for sharing his knowledge of Arctic ecosystems; Julie McIntyre for helping with the statistics; and Chris Zinszer and JoAnna LaBelle for their field and laboratory assistance.