Access

You are not currently logged in.

Access JSTOR through your library or other institution:

login

Log in through your institution.

Amino Acid Absorption by Arctic Plants: Implications for Plant Nutrition and Nitrogen Cycling

Knut Kielland
Ecology
Vol. 75, No. 8 (Dec., 1994), pp. 2373-2383
Published by: Wiley
DOI: 10.2307/1940891
Stable URL: http://www.jstor.org/stable/1940891
Page Count: 11
  • Download ($42.00)
  • Subscribe ($19.50)
  • Cite this Item
Amino Acid Absorption by Arctic Plants: Implications for Plant Nutrition and Nitrogen Cycling
Preview not available

Abstract

Recent studies of nitrogen (N) cycling in arctic tundra have indicated that inorganic N supplied to plants by mineralization is not sufficient to meet the annual requirement of N by many tundra species. Whereas N mineralization is slow in tundra soils and concentrations of inorganic N are low, these soils have large stocks of both structural and soluble organic N. In light of these observations, kinetics of absorption of three amino acids (glycine, aspartic acid, and glutamic acid) were measured in dominant vascular plant species of the four major ecosystems types in arctic Alaska and compared with concentrations of free amino acids in soils. Absorption rates were measured on roots using ^1^4C-labeled substrates. Concentrations of free amino acids in soil were measured on water-extracted samples by high pressure liquid chromatography. All species had higher capacity (V"m"a"x) for ammonium uptake (measured using methylamine as an ammonium analogue) than for any amino acid. However, at concentrations observed in the field, uptake rates estimated for amino acids were similar to (glycine) or less than (aspartic and glutamic acids) that for ammonium. On the basis of these comparisons, uptake rates of the three amino acids together may account for between 10 and 82% of the total N uptake in the field, depending on species and community. Deciduous shrubs had higher uptake rates than the more slowly growing evergreen shrubs, suggesting that new growth created a sink that strongly influenced capacity for amino acid uptake. In general, ectomycorrhizal species had higher amino acid uptake than did non-mycorrhizal species. In species that were sampled from more than one community, amino acid uptake rates were highest in the community where a given amino acid was most abundant in the soil. The results indicate that, in arctic tundra, plants short-circuit the mineralization step of decomposition by directly absorbing amino acids. This implies that in the organic soils of these tundra systems (1) inorganic nitrogen is an inadequate measure of plant-available soil nitrogen, (2) mineralization rates underestimate nitrogen supply rates to plants, (3) the large differences among species in capacities to absorb different forms of N provide ample basis for niche differentiation of what was previously considered a single resource, and (4) by short-circuiting N mineralization, plants accelerate N turnover and effectively exert greater control over N cycling than has been previously recognized.

Page Thumbnails

  • Thumbnail: Page 
2373
    2373
  • Thumbnail: Page 
2374
    2374
  • Thumbnail: Page 
2375
    2375
  • Thumbnail: Page 
2376
    2376
  • Thumbnail: Page 
2377
    2377
  • Thumbnail: Page 
2378
    2378
  • Thumbnail: Page 
2379
    2379
  • Thumbnail: Page 
2380
    2380
  • Thumbnail: Page 
2381
    2381
  • Thumbnail: Page 
2382
    2382
  • Thumbnail: Page 
2383
    2383