PARENT SESSION
Oral Session #76: Plant Ecology: Nutrient Uptake, Movement, Use. Presiding: J. Schade.
Friday, August 10, 2001. 8:00 AM to 11:45 AM. Hall of Ideas G.

Free amino acids as a source of plant nitrogen nutrition in sub-arctic salt-marsh coastal sites.

HENRY, HUGH¹, JEFFERIES, ROBERT¹, ¹

ABSTRACT- The role of free soil amino acids in plant nitrogen nutrition was investigated in a coastal sub-arctic salt-marsh. In order to test the hypothesis that free amino acids are an important contributor to plant growth in these systems, we quantified the concentrations of free amino acids and inorganic nitrogen present in the soil on a seasonal basis from an analysis of soil water extracts. We also determined the uptake rates of ¹⁵N-labelled amino acids and inorganic nitrogen by roots excised from tillers of Puccinellia phryganodes grown in hydroponic culture. Free amino acid concentrations relative to soluble ammonium were high throughout the growing season, especially in the intertidal zone, where the median ratio of amino acids to ammonium ions was 0.36 and amino acid concentrations in soil water exceeded those of ammonium ions for 24% of all samples. The maximum uptake rate of ammonium (73 micromoles/g/h) exceeded that of the amino acid glycine (15 micromoles/g/h). However, the affinity of roots for ammonium (Km = 57 micromoles) was lower than that of glycine (Km = 41). At high salinity (150 mM NaCl), rates of ammonium and glycine uptake were reduced by 22% and 14% respectively. By modeling plant nitrogen uptake based on soil solution concentrations and root uptake rates, it was estimated that free amino acids contribute substantially to the annual nitrogen uptake of sub-arctic salt-marsh graminoids.

KEY WORDS: free amino acids, root uptake, arctic, nitrogen