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Environmental Controls Over Carbon, Nitrogen and Phosphorus Fractions in Eriophorum Vaginatum in Alaskan Tussock Tundra

F. S. Chapin III, G. R. Shaver and R. A. Kedrowski
Journal of Ecology
Vol. 74, No. 1 (Mar., 1986), pp. 167-195
DOI: 10.2307/2260357
Stable URL: http://www.jstor.org/stable/2260357
Page Count: 29
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Environmental Controls Over Carbon, Nitrogen and Phosphorus Fractions in Eriophorum Vaginatum in Alaskan Tussock Tundra
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Abstract

(1) In Alaskan tussock tundra the seasonal pattern of most carbon-, nitrogen- and phosphorus-containing chemical fractions was followed for 3 years in Eriophorum vaginatum and the response of these fractions to manipulation of light intensity, air temperature, nutrient availability and repeated clipping was examined. (2) In control plants, total-carbohydrate concentration was high (30-35% in stems) and fluctuated less than 10% throughout the growing season, indicating that current photosynthate was adequate to meet concurrent growth demands. Normal yearly variations in growing conditions caused greater change in carbohydrate concentrations than did any manipulation (including 50% reduction in irradiance) except repeated clipping. Carbohydrate reserves returned to control levels following 1 year of recovery from clipping. (3) Lipid was low in concentration and present mainly as phospholipids and waxes rather than as storage triglycerol. Lipid, soluble phenolic and tannin concentrations were not strongly affected by any manipulation, even those that strongly reduced carbohydrate reserves, indicating that these carbon fractions were not tightly tied to the plant carbon-nutrient balance. (4) Nitrogen was stored during winter mainly as arginine in stems--glutamine, asparagine, proteins and nucleic acids also increased to a lesser extent. The 400% seasonal fluctuation in amino-acid N reserves of stems (vs. 10% in carbohydrates) indicates that N reserves were depleted much more strongly than carbohydrate reserves to support spring growth. In leaf blades, N was present mainly in protein and to a lesser extent in fractions such as nucleic acids that are associated with protein synthesis. Nitrate was undetectable in all tissues, and ammonium N was always less than 2% of total N. (5) Phosphorus was stored during winter as a stable, soluble, organic-P compound. Phytic acid was absent from all tissues, and inorganic P was involved in short-term storage at times of temporary-P excess during the growing season rather than in winter storage. Lipid P increased in autumn, reflecting its role in cold hardiness. (6) Changes in N- and P-containing fractions in response to manipulation of light, temperature, nutrients and clipping generally reflected changes in plant nutrient status rather than specific responses to each manipulation. Thus, improved nutrient status generally caused an increase in all N- and P-containing fractions, particularly amino-acid N and soluble-organic P of stems and inorganic P of leaf blades. (7) In leaf blades, all organic N and P fractions (except amino-acid N, the form in which N is translocated) decreased to a similar extent during senescence, suggesting that retranslocation from leaves is unaffected by the hydrolysability of different N and P fractions. (8) The growth rate of E. vaginatum in Alaskan tundra is probably controlled mainly by the availability of internal nutrient reserves rather than by any effect of temperature upon synthesis or transport of organic-carbon compounds required for growth. In spring, internal nutrient reserves from stems support a near-maximal growth rate. In late summer, growth slows because nutrient accumulation in stems takes precedence over its incorporation in growth. If nutrient availability increases in late summer, continued growth is possible, because the nutrient demands of both storage and growth can be met.

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