Regulation of amino acid biodegradation in soil as affected by depth |
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Authors: | Sarah J Kemmitt David Wright Daniel V Murphy David L Jones |
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Institution: | (1) School of the Environment & Natural Resources, University of Wales, Bangor, Gwynedd, LL57 2UW, UK;(2) School of Earth and Geographical Sciences, The University of Western Australia (MO87), Crawley, WA, 6009, Australia |
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Abstract: | Dissolved organic nitrogen (DON) and in particular free amino acids represent a key pool in the terrestrial soil C and N cycle.
The factors controlling the rate of turnover of this pool in soil, however, remain poorly understood. We investigated the
factors regulating the rate of amino acid turnover at different depths (up to 1.2 m) in five low-input, acid soil profiles.
Within the root zone (0–60 cm), amino acids constituted 8% of the DON and represented only a small fraction of plant available
N. In all the soil profiles, the rate of amino acid mineralisation decreased progressively with depth. The average half-life
of the exogenously added amino acids in the soil was 5.8 h in topsoils (0–10 cm), falling to 20 h at a depth of 50 cm and
to 33 h at 100 cm. Generally, the rate of amino acid mineralisation correlated positively with total soil C and N, soil microbial
activity (basal soil respiration rate) and soil content. The relatively rapid rates of microbial amino acid assimilation in subsoils below the root zone (>60 cm) indicate
that long-term transport of amino acids (e.g. from soil to freshwaters) will be low. Based upon the C-to-N ratio of the amino
acid substrate and the microbial C assimilation efficiency, we estimate that approximately 40–60% of the amino acid-N will
be excreted as . In conclusion, the rapid rate of free amino acid turnover and their low concentration in soil solution indicate that the
formation of inorganic N ( and ) in soil is limited primarily by the rate of free amino acid appearance in soil and not by the rate of amino acid mineralisation. |
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Keywords: | Ammonium Dissolved organic carbon DOC DON Immobilisation Mineralisation Nitrate Soil solution Vadose zone |
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