NITROGEN UPTAKE BY ARCTIC SOIL MICROBES AND PLANTS IN RELATION TO SOIL NITROGEN SUPPLY

In Alaska, evergreen and deciduous shrubs dominate the vegetation of moist acidic arctic tundra (soil pH 5.5). In this study we compare soil concentrations and microbial and plant uptake of amino acids, ammonium (NH4+), and nitrate (NO3−) in acidic and nonacidic tundra. The objective was to determine any differences between the tundra sites that may relate to the differences in vegetation. We sampled the water-extractable soil N pool over one growing season and found that it at all times was higher at the nonacidic than at the acidic site, while at both sites it was dominated by NH4+ followed in order by amino acid N and NO3−. In addition, we designed an experiment in which a mixture of aspartic acid, glycine, NH4+, and NO3− were injected into the soil in the middle of the growth period. In the mixture, one N form at a time was labeled with 15N and in the case of amino acids also with 13C. Soi...