Constraints to Nitrogen Fixation by Cryptogamic Crusts in a Polar Desert Ecosystem, Devon Island, N.W.T., Canada

2000 ◽  
Vol 32 (1) ◽  
pp. 40 ◽  
Author(s):  
Leal G. Dickson
Keyword(s):  
Nitrogen Fixation ◽  
Desert Ecosystem ◽  
Polar Desert ◽  
Devon Island ◽  
Cryptogamic Crusts

Vascular plant reproduction, establishment, and growth and the effects of cryptogamic crusts within a polar desert ecosystem, Devon Island, N.W.T., Canada

1999 ◽  
Vol 77 (5) ◽  
pp. 623-636 ◽  
Author(s):  
L C Bliss ◽  
W G Gold
Keyword(s):  
Plant Reproduction ◽  
High Arctic ◽  
Degree Days ◽  
Polar Desert ◽  
Devon Island ◽  
Warm Summer ◽  
Viable Seeds ◽  
Desert Landscape ◽  
Cryptogamic Crusts ◽  
Cryptogamic Crust

Most of the ice-free lands within the Canadian High Arctic are classified as polar desert (44%) or semidesert (49%). Much of this desert landscape supports no more than 6-10 vascular species that provide 1-3% cover and cryptogamic organisms that occupy 0-5% cover on the soil surface. The barrenness of these lands results from a short growing season and low summer temperatures that limit plant growth and the production of viable seeds. Limited areas have a 50-80% cover of cryptogamic crust and an 8-12% cover of vascular plants. These are areas in which surfaces remain moist for considerable periods in summer from snowflush waters. Where such cryptogamic soil crusts develop, they play a central role in soil development and nitrogen fixation. The two major components of this study were (i) an examination of fundamental reproductive, establishment, and growth characteristics of polar desert plants in the field and (ii) the relationship of these characteristics to environmental conditions in areas with and without cryptogamic crusts. Summer conditions during the study ranged from unusually warm (1991; 252 degree-days) to unusually cool (1992; 123 degree-days) with two average years (1994 and 1995; 172 and 166 degree-days, respectively). Differences in reproduction and establishment among these summers included (i) higher germination ability of seeds produced in the warm summer (1991) compared with more average summers (1994 and 1995) and (ii) significant seedling occurrence only in the average summers of 1994 and 1995. Seedling densities were much higher at crusted (206 seedlings/m2) than noncrusted sites (26 seedlings/m2). In both sites, root elongation of seedlings and older plants were significantly greater than shoot elongation, yet in established plants, shoot biomass was much greater than root biomass (root/shoot ratios from 0.1 to 0.3). Reproductive attributes varied among the species examined. Saxifraga caespitosa L. produced much smaller seeds then Draba corymbosa R. Br. ex DC. and Papaver radicatum Rottb., but the largest seeds of S. caespitosa (produced in the warm summer of 1991) had much higher germination rates than any seeds of the other species. Based on an analysis of population age structures, seedling survivorship was low for all species but was especially low for S. caespitosa, despite its higher germination rates. All species were slow to germinate, with isolated seeds under ideal controlled conditions requiring a minimum of 20-30 days at a 20°C day and 15°C night. Seed germination in excised soil blocks under comparable conditions averaged 36-48 days. We believe these polar desert plant species lack special attributes to uniquely exploit the environment of these very stressful locations. Rather, they are simply adept at surviving the rigors experienced there. The same species grow much larger, flower and fruit more abundantly, and produce more viable seeds in high arctic environments more favorable than polar deserts, such as lowland polar oases (e.g., Truelove Lowland, Devon Island, Canada). Within the harsh polar desert landscape of the High Arctic, the presence of a cryptogamic crust that retains surface moisture, prevents soil churning, and includes nitrogen-fixing organisms provides a more favorable habitat for plant reproduction, establishment, and growth.Key words: High Arctic, plant reproduction, plant establishment, plant growth, cryptogamic crust, polar desert, Devon Island.

Nitrogen fixation and photosynthesis in high arctic forms of Nostoc commune

1994 ◽  
Vol 72 (7) ◽  
pp. 940-945 ◽  
Author(s):  
R. Lennihan ◽  
D. M. Chapin ◽  
L. G. Dickson
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Terrestrial Ecosystems ◽  
Growing Season ◽  
High Arctic ◽  
Colony Morphology ◽  
Nostoc Commune ◽  
Devon Island ◽  
Low Levels ◽  
Temperature Optima

Nostoc commune, a colonial cyanobacterium, has been suggested as an important contributor of nitrogen to terrestrial ecosystems in the Canadian High Arctic, yet little is known about the ecophysiology of this organism in arctic environments. This study focused on the physiological performance of macroscopic colonies of N. commune found on Devon Island, N.W.T. The objectives were to examine the influence of temperature, colony morphology, and seasonal phenology on nitrogen fixation rates and the effects of light and temperature on photosynthesis. Maximum rates of acetylene reduction in N. commune (2119 nmol C2H4∙g−1∙h−1) were higher than those previously recorded for arctic N. commune but lower than values reported for temperate poulations. Depending on the time of the growing season, the temperature optimum for acetylene reduction varied from 15 °C to greater than 20 °C. Photosynthetic temperature optima did not occur below 20–25 °C (the highest temperatures measured). Light saturation of photosynthesis was reached at low levels of irradiance (100–150 μmol∙m−2∙s−1 PPFD). Acetylene reduction rates varied strongly with colony morphology. Thin, fragile, flattened colonies had higher rates than thicker, more resilient, flattened colonies or spherical colonies. Cold post-thaw temperatures appeared to delay the recovery of maximum nitrogen fixation rates for 2–3 weeks following the onset of the growing season. Compared with two other species of cyanobacteria present on Truelove Lowland (Gloeocapsa alpina and Gleotrichia sp.), N. commune had higher rates of nitrogen fixation. Key words: Nostoc commune, cyanobacteria, High Arctic, nitrogen fixation, photosynthesis.

Thawing permafrost alters nematode populations and soil habitat characteristics in an Antarctic polar desert ecosystem

Pedobiologia ◽  
2012 ◽  
Vol 55 (2) ◽  
pp. 75-81 ◽  
Author(s):  
T.E. Smith ◽  
D.H. Wall ◽  
I.D. Hogg ◽  
B.J. Adams ◽  
U.N. Nielsen ◽  
...  
Keyword(s):  
Habitat Characteristics ◽  
Desert Ecosystem ◽  
Polar Desert ◽  
Thawing Permafrost ◽  
Soil Habitat

scholarly journals Microbiology and Vegetation of Micro-oases and Polar Desert, Haughton Impact Crater, Devon Island, Nunavut, Canada

2001 ◽  
Vol 33 (3) ◽  
pp. 306-318 ◽  
Author(s):  
Charles S. Cockell ◽  
Pascal Lee ◽  
Andrew C. Schuerger ◽  
Loretta Hidalgo ◽  
Jeff A. Jones ◽  
...  
Keyword(s):  
Impact Crater ◽  
Polar Desert ◽  
Devon Island
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