Information on the contribution of amino acids to dissolved organic nitrogen and carbon
exported from grassland soil is scarce. Evidence from the literature for other
environments, suggests that determination of amino acid patterns of distribution may be a
useful method for improved understanding of the interaction of microbial synthesis and
degradation of organic N in conjunction with soil physical states.
A sample pre-concentration technique and an HPLC methodology were developed that
enabled the determination of dissolved free (DFAA) and combined (DCAA) amino acids in
natural waters at picomolar concentration. These methods were used to examine the
content of amino acids and their distribution patterns in waters from 3 different settings.
Firstly, field-sized lysimeters (1 ha) were used to examine dissolved free and combined
amino acids in surface runoff and drainage waters from a grassland soil over 3 winter
drainage periods. The waters were collected from soils beneath drained and undrained
permanent ryegrass swards, receiving 280 kg N haˉ¹yrˉ¹
, permanent ryegrass receiving
no mineral N input, and grass/white clover (no mineral N). Total DFAA concentration
ranged between 1.9 nM - 6.1 µM and total DCAA concentration ranged between 1.3 - 87
µM. A large library of amino acid distributions was assembled and multivariate pattern
analysis techniques were used to determine whether there were distinctive amino acid
signatures that could be used as a diagnostics for soil management and condition.
Although addition of mineral N fertilizer increased amino acid concentration in waters,
there was no detectable effect of fertilizer addition on DFAA distribution patterns. In
contrast, both DFAA and DCAA patterns were strongly influenced by soil hydrology alone.
However, in the case of DCAA patterns, there was evidence of an interaction between
hydrology and fertilizer addition.
Secondly, monolith lysimeters were used to determine the DFAA in drainage waters from
4 different grassland soil types, in order to find whether there was evidence of pattern
difference with soil texture. Results showed that distribution patterns vary between soil
types, and contrary to what might be expected, that clay soils do not necessarily retain
basic amino acids.
Thirdly, the concentration and patterns of DFAA were determined hourly over a 24 hour
period, for a river that received exported soil waters from the field lysimeters mentioned
above. Total DFAA concentration correlated with water temperature and NH4+ Compared
with exported soil waters, the concentrations of DFAA in river water were several orders of
magnitude smaller, although GLY, SER, LYS and MET were in greater relative
proportions.
Results of the studies show that amino acids have the potential to be used as diagnostics
of source, soil condition and management.BBSRC Institute of Grassland and Environmental Researc
