Role of free amino acids in the nitrogen economy of arctic cryptogams

Absorption kinetic experiments with two arctic cryptogams (Sphagnum rubellum and Cetraria richardsonii) coupled with data on soil nitrogen, strongly suggest that organic nitrogen is a major component of the nitrogen budget of these species. Both species had substantially higher absorption capacities for the amino acid glycine than for methylamine, an ammonium analogue. Absorption experiments with aspartate and glutamate, demonstrate that higher-molecular weight amino acids also can be absorbed at substantial rates compared to inorganic nitrogen. Nitrogen isotope values (delta(15)N) in the present species are significantly lower than in graminoids, but similar to deciduous shrubs that also show high capacity for amino acid absorption. Notwithstanding considerable interspecific variation in the capacity to absorb amino acids among tundra species, the manifestation of this physiological characteristic across five major growth forms in the Arctic, suggests that the uptake of organic nitrogen is a general adaptive syndrome of arctic plants.