In-situ root uptake and soil transformations of glycine, glutamine and ammonium in two temperate deciduous forests of contrasting N availability

摘要

Whereas it is recognized that most trees have the capacity to take up free amino acids, it is unclear how important amino acid uptake is in situ. In-situ root uptake of isotopically-labeled ammonium, glycine and glutamine were compared between low-nitrogen (N)-availability and high-N-availability temperate forests. Comparable immediate C-13- and N-15-enrichment of fine roots indicated that short-term uptake of amino-acids by tree roots was similar between the two sites. Over the remainder of the experiment, recovery of amino-acid N-15 in fine roots was greater, and recovery of C-13 lower, in the high-N-availability site. Together with greater rates of conversion of amino-acid-derived N-15 into inorganic forms, this indicates that a greater proportion of amino-acid-derived N was taken up after it was converted to inorganic forms by soil microorganisms in the high N availability site. Results from this study suggest that capacity for amino acid uptake by tree roots did not differ between high- and low-N availability sites, but differences in microbial mineralization drove strong differences in the availability of inorganic forms of N between sites