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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 77 (1988), S. 506-514 
    ISSN: 1432-1939
    Keywords: Carbohydrate ; Growth form ; Nitrogen ; Phosphorus ; Tundra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In a survey of 28 plant species of 6 major growth forms from Alaskan tundra, we found no consistent difference among growth forms in the chemical nature of stored reserves except for lichens and mosses (which stored C primarily as polysaccharides) and shrubs (which tended to store C more as sugars than as polysaccharides). Forbs and graminoids showed particularly great diversity in the chemical nature of stored reserves. In contrast, C, N, and P chemistry of leaves was strikingly similar among all species and growth forms. Concentrations of stored reserves of C, N, and P were highest and showed greatest seasonal fluctuations in forbs and graminoids but were relatively constant in evergreen shrubs. From this information, we draw three general conclusions: (1) the photosynthetic function of leaves strongly constrains leaf chemistry so that similar chemical composition is found in all species and growth forms: (2) the chemical nature of storage reserves is highly variable, both within and among growth forms; (3) the concentration and seasonal pattern of storage reserves are closely linked to growth-form and reflect growth-form differences in woodiness, phenology, and relative dependence upon concurrent uptake vs. storage in support of growth.
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  • 2
    ISSN: 1432-1939
    Keywords: Mosses ; Mycorrhizae ; Phosphorus cycling ; Picea mariana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mosses account for 75% of the annual phosphorus accumulation in aboveground parts of an Alaskan black spruce forest, although they comprise only 17% of the phosphorus pool in aboveground vegetation. Sphagnum subsecundum and feathermosses (Hylocomium splendens and Pleurozium schreberi) have a higher capacity to absorb phosphate than do the fine roots of black spruce (Picea mariana) that are situated beneath the moss layer. In three of the four moss species studied, phosphate absorption capacity increases with increasing age of green tissue and decreases with increasing age of brown tissue. In the two feathermosses, which acquire moisture primarily from the air, and in Sphagnum, phosphate absorption is more rapid in green than in brown tissue. In contrast, the endohydric moss Polytrichum commune, which transports water through stem tissue from soil, absorbs phosphate most rapidly from stems in mineral soil. Two treatments designed to reduce activity of mycorrhizae (cutting of roots extending beneath the moss carpet or application to the moss surface of a fungicide that kills mycorrhizal hyphae) tended to increase phosphate retention by mosses and reduce phosphate transfer out of the experimental plots. This suggests that mycorrhizae are an important avenue of phosphorus movement out of the moss carpet and a means by which the black spruce competes with the overlying mosses for nutrients.
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  • 3
    ISSN: 1432-1939
    Keywords: Eriophorum vaginatum ; E. scheuchzeri ; Growth ; Flowering ; Phenology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The evergreen tussock-forming Eriophorum vaginatum revealed consistently earlier (c. 1 moth) phenology and greater biomass per tiller than the summergreen rhizomatous E. scheuchzeri in all four components measured (vegetative and reproductive shoots and stems) under the same climatic regime in central Alaska over one growing season. Greatest allocation to vegetative shoot growth occurred in mid-summer in both species. The tussock growth form of E. vaginatum raised shoot meristems 25–30 cm above the soil surface, where temperatures were warmer, permitting shoot growth to begin earlier in spring and continue longer in autumn than in E. scheuchzeri. Consequently, E. vaginatum was able to allocate reserves to reproductive tillers primarily in autumn and early spring, times when minimal reserves were required for vegetative growth. By contrast, the rhizomatous E. scheuchzeri had a more constrained growing season, and allocation to reproduction coincided with allocation to vegetative growth. For this reason, reserves were drawn down more fully in mid-summer in E. scheuchzeri than in E. vaginatum. The more conservative use of nutrient stores in E. vaginatum may relate to its great longevity, reduced allocation to reproduction (including low seedling recruitment), and relatively stable habitats. The mid-seasonal pulse of allocation to reproduction in E. scheuchzeri appears viable only in relatively fertile disturbed sites, where the soil nutrient supply is sufficient to support simultaneous allocation to vegetative growth and reproduction.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 79 (1989), S. 412-416 
    ISSN: 1432-1939
    Keywords: Alder ; Competition ; Growth ; Regular spacing ; Tundra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Alders (Alnus crispa) in shrub tundra in northern Alaska showed significant regularity of spacing. Removal of neighboring alder shrubs stimulated nutrient accumulation and growth of remaining alders but did not stimulate nutrient accumulation or growth of any other shrub species. This demonstrates that neighboring alders competed with one another and that, when alders were removed, the resources made available were used preferentially by remaining alders rather than by the community in general. Neither patterns of seedling establishment nor patterns of frostrelated features could explain the regular distribution of alder. We suggest that regular patterns of plant distribution are restricted to sites of low-resource availability, because in these habitats (1) there is strong competition for a scarce resource, and (2) there are only one or a few dominant species to compete for these resources in a given canopy height or rooting depth.
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  • 5
    ISSN: 1432-1939
    Keywords: Snowshoe hare ; Birch ; Alder ; Chemical defense ; Plant carbon/nutrient balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plant carbon/nutrient balance has been implicated as an important factor in plant defensive chemistry and palatability to herbivores. We tested this hypothesis by fertilizing juvenile growth form Alaska paper birch and green alder with N, P and N-plus-P in a balanced 2x2 factorial experiment. Additionally, we shaded unfertilized plants of both species. Fertilization with N and N-plus-P increased growth of Alaska paper birch, reduced the concentration of papyriferic acid in internodes and increased the palatability of birch twigs to snowshoe hares. Shading decreased birch growth, decreased the concentration of papyriferic acid in internodes and increased twig palatability. These results indicate that the defensive chemistry and palatability of winter-dormant juvenile Alaska paper birch are sensitive to soil fertility and shade. Conversely the defensive chemistry and palatability of green alder twigs to snowshoe hares were not significantly affected by soil fertility or shade. The greater sensitivity of Alaska paper birch defensive chemistry and palatability to snowshoe hares in comparison to green alder is in agreement with the hypothesis that early successional woody plants that are adapted to high resource availability are more plastic in their chemical responses to the physical environment than are species from less favorable environments.
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  • 6
    ISSN: 1432-1939
    Keywords: Defoliation ; Compensatory growth ; Serengeti ; Phosphate uptake ; Nutrient deficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two shortgrass species (Sporobolus ioclados and Eustachys paspaloides) and two midgrass species (E. paspaloides and Pennisetum mezianum) from the Serengeti grasslands of Tanzania were grown under conditions of extreme phosphorus (P) deficiency. Production of each of these species is maintained or enhanced by defoliation under adequate nutrient supply (McNaughton et al. 1983). However, under the P-deficient conditions of our experiment, defoliation caused a reduction in biomass of all plant parts of each species. Green leaf biomass was reduced most strongly by defoliation, and crowns were least affected. Yield of biomass and nutrients to grazers (green leaves+clipped material) was enhanced by weekly defoliation in the shortgrass grazing-adapted species, whereas yield to producers (live biomass and nutrients retained by the plant) and yield to decomposers (litter) were strongly reduced by defoliation in all species. Phosphate absorption capacity (V max) measured on excised roots was enhanced by defoliation in the grazing-adapted Sporobolus, but, due to low affinity (high K m) of roots of defoliated plants for phosphate, absorption rate was not greatly altered at low solution concentrations. Phosphate absorption capacity was reduced or unaffected by defoliation in other species. We conclude that under conditions of P deficiency, plants are unable to acquire the nutrients necessary to replenish large nutrient losses to grazers. In low-nutrient environments, compensatory growth (stimulation of production by grazing) is not a viable strategy. Therefore, in these environments plants respond evolutionarily to herbivores by developing chemical or morphological defenses.
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  • 7
    ISSN: 1432-1939
    Keywords: Allocation ; Growth ; Phosphorus ; Photosynthesis ; Seed size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Under favorable nutrition, accessions of the weedy barleygrass (Hordeum leporinum and H. glaucum) had a higher relative growth rate (RGR) than did accessions of cultivated barley (H. vulgare) or its wild progenitor (H. spontaneum). RGR was not positively correlated with the presumed level of soil fertility at the collection site of an accession either within or among species. RGR was reduced more strongly by low-P supply in the progenitor than in the crop or weed, indicating that selection of cultivars to grow in fertile soils had not reduced their potential to grow effectively under low-P conditions. Seed and embryo masses were more important than RGR in determining plant size. Relative differences among assessions in plant size declined with time, because (1) accessions with small seeds had a higher RGR, and (2) RGR of large-seeded accessions declined with time. Absolute growth rate correlated positively with leaf area and negatively with photosynthetic rate per unit leaf area. Under favorable nutrition, maximum photosynthetic rate correlated negatively with leaf length and therefore was higher in the weeds than in the crop or progenitor accessions. P absorption potential did not differ consistently among species but generally increased in response to P stress. Cultivars produced a few tall tillers, whereas weeds and progenitors produced many small tillers. The cultivar had a larger proportion of reproductive tillers, allocated a larger proportion of biomass to grain, and produced larger grains than did the weedy accession. By contrast, the weed began maturing seeds sooner, produced more reproductive tillers, and produced more grains per car and per plant than did the cultivar. The study suggests two major conclusions: (1) A low RGR is not an adaptation to low P supply in annual Hordeum species. (2) Seed size is the major determinant of early plant size between accessions in these Hordeum species under favorable nutrition. However, large seed size indirectly results in a low RGR because of the inverse relationship between plant size and RGR and results in a low photosynthetic rate because of the inverse relationship between leaf size and photosynthesis.
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  • 8
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
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