The Fate of Amino Acid in Soil Experiments: Bacteria, Roots and Fungi

Organic nitrogen (ON) is the most common form of nitrogen in the soil. If this form is the most abundant then many new questions must be addressed in order to fully understand the breakdown of ON such as what organisms are incorporating the nitrogen, the rate of uptake and the effect of concentration on uptake rate. Many measurements have been made regarding the uptake rate of amino acid in soil using radioactive isotopes, however many experiments use only one relatively large concentration. Concentration greatly affects the results and uptake rate by soil, microorganisms and plant roots, and organisms behave differently when different concentrations of free amino acids are present. In soil, bacteria are the most abundant at 0.7 x 10, and roots (largely with mycorrhizal fungal associations) comprise 1.2% of soil content. Five different concentrations (100nM, 1, 10, 100, 150 μM) of 14C labeled leucine were tested to determine the uptake rate in roots with and without mycorrhizae, and roots from cucumber plant grown in the lab in sterile medium (coarse sands) to prevent endomycorrhizal symbiosis. Roots with mycorrhizal associations are able to take up the greatest amount of amino acid and therefore have an advantage over roots without mycorrhizal associations. Roots without mycorrhizae and cucumber roots took up much less amino acid than the roots with mycorrhizae at all concentrations. In nature, it is likely that most free amino acids in soils are taken up by microorganisms (including fungi) or become hidden in soil micropores, leaving plants starved of free amino acid. Concentrations must be chosen with great concern when assessing uptake rate of amino acid in soil, roots and microorganisms because different results will form if different concentrations are used.