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91.
Mosses dominate many northern ecosystems and their presence is integral to soil thermal and hydrological regimes which, in
turn, dictate important ecological processes. Drivers, such as climate change and increasing herbivore pressure, affect the
moss layer thus, assessment of the functional role of mosses in determining soil characteristics is essential. Field manipulations
conducted in high arctic Spitsbergen (78° N), creating shallow (3 cm), intermediate (6 cm) and deep (12 cm) moss layers over
the soil surface, had an immediate impact on soil temperature in terms of both average temperatures and amplitude of fluctuations.
In soil under deep moss, temperature was substantially lower and organic layer thaw occurred 4 weeks later than in other treatment
plots; the growing season for vascular plants was thereby reduced by 40%. Soil moisture was also reduced under deep moss,
reflecting the influence of local heterogeneity in moss depth, over and above the landscape-scale topographic control of soil
moisture. Data from field and laboratory experiments show that moss-mediated effects on the soil environment influenced microbial
biomass and activity, resulting in warmer and wetter soil under thinner moss layers containing more plant-available nitrogen.
In arctic ecosystems, which are limited by soil temperature, growing season length and nutrient availability, spatial and
temporal variation in the depth of the moss layer has significant repercussions for ecosystem function. Evidence from our
mesic tundra site shows that any disturbance causing reduction in the depth of the moss layer will alleviate temperature and
moisture constraints and therefore profoundly influence a wide range of ecosystem processes, including nutrient cycling and
energy transfer. 相似文献
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Respiratory and cardiac activity of killer whales 总被引:2,自引:0,他引:2
95.
Menna E. Jones Peter J. Jarman Caroline M. Lees Heather Hesterman Rodrigo K. Hamede Nick J. Mooney Dydee Mann Chrissy E. Pukk Jemma Bergfeld Hamish McCallum 《EcoHealth》2007,4(3):326-337
An emerging infectious facial cancer threatens Tasmanian devils with extinction. The disease is likely to occur across the
range of the devil within 5 years. This urgent time frame requires management options that can be implemented immediately:
the establishment of insurance populations, in captivity, wild-living on islands, and aiming for eradication in areas that
can be isolated. The long-term options of the spontaneous or assisted evolution of resistance or development of a field-deliverable
vaccine are unlikely to be available in time. The disease’s characteristic allograft transmission through intimate contact
simplifies isolation of insurance populations and breaking transmission in suppression trials. Better knowledge of contact
matrices in wild devils will help focus timing and demographic targets of removals. A metapopulation approach is needed that
integrates captive and wild-living island and peninsula (disease suppression) populations to minimize the loss of genetic
diversity over 50 years until either extinction and reintroduction can occur, resistance evolves or a field-deliverable vaccine
is developed. Given the importance of the insurance populations and the low genetic diversity of devils, a conservative target
for retention of 95% genetic diversity is recommended. Encouraging preliminary results of the first disease-suppression trial
on a large peninsula show fewer late stage tumors and no apparent population decline. Limiting geographic spread or suppressing
the disease on a broadscale are both unlikely to be feasible. Since the synergy of devil decline and impending fox establishment
could have devastating consequences for Tasmanian wildlife, it is crucial to manage the dynamics of new and old predator species
together. 相似文献
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Alterations in lipid composition of plasma lipoproteins during deposition of egg yolk 总被引:2,自引:0,他引:2
The profiles of total lipids and of the molecular species of individual lipid classes were compared among corresponding lipoproteins of plasma and yolk of the laying hen. A close qualitative correspondence was found in the makeup of the molecular species of glycerophospholipids and triglycerides of the very low density lipoproteins and the high density lipoproteins of plasma and yolk. There was a lower proportion of the trienoic triglycerides and of the dienoic glycerophospholipids in the egg yolk than in the plasma lipoproteins, and the greatest differences (20-30%) were noted between the high density lipoproteins. It was also observed that the plasma high density lipoproteins lost their cholesteryl esters upon entering the yolk. On the basis of these and comparable analyses of the plasma lipoproteins of the nonlaying hen, it is concluded that the laying hen synthesizes specific lipoproteins for deposition in the yolk, and these are carried in plasma and selectively transferred to the developing ovum without significant equilibration with the other plasma lipoproteins. 相似文献
100.
Balancing positive and negative plant interactions: how mosses structure vascular plant communities 总被引:1,自引:0,他引:1
Our understanding of positive and negative plant interactions is primarily based on vascular plants, as is the prediction
that facilitative effects dominate in harsh environments. It remains unclear whether this understanding is also applicable
to moss–vascular plant interactions, which are likely to be influential in low-temperature environments with extensive moss
ground cover such as boreal forest and arctic tundra. In a field experiment in high-arctic tundra, we investigated positive
and negative impacts of the moss layer on vascular plants. Ramets of the shrub Salix polaris, herb Bistorta vivipara, grass Alopecurus borealis and rush Luzula confusa were transplanted into plots manipulated to contain bare soil, shallow moss (3 cm) and deep moss (6 cm) and harvested after
three growing seasons. The moss layer had both positive and negative impacts upon vascular plant growth, the relative extent
of which varied among vascular plant species. Deep moss cover reduced soil temperature and nitrogen availability, and this
was reflected in reduced graminoid productivity. Shrub and herb biomass were greatest in shallow moss, where soil moisture
also appeared to be highest. The relative importance of the mechanisms by which moss may influence vascular plants, through
effects on soil temperature, moisture and nitrogen availability, was investigated in a phytotron growth experiment. Soil temperature,
and not nutrient availability, determined Alopecurus growth, whereas Salix only responded to increased temperature if soil nitrogen was also increased. We propose a conceptual model showing the relative
importance of positive and negative influences of the moss mat on vascular plants along a gradient of moss depth and illustrate
species-specific outcomes. Our findings suggest that, through their strong influence on the soil environment, mat-forming
mosses structure the composition of vascular plant communities. Thus, for plant interaction theory to be widely applicable
to extreme environments such as the Arctic, growth forms other than vascular plants should be considered. 相似文献