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P.J. Chapmanet al.
Dissolved Organic Nitrogen in a PeatyPodzol
4.3
Dissolved Organic Nitrogen
in a Peaty Podzol: Influence
of Temperature and Vegetation
Cover
P.J. C
HAPMAN
1,2
, B.L. W
ILLIAMS
1
AND
A. H
AWKINS
1
1
Macaulay Land Use Research Institute,Craigiebuckler, Aberdeen
AB15 8QH;
2
Present address: School of Geography, University of
Leeds, Leeds LS2 9JT, UK
Introduction
In most soils, > 90% of the nitrogen is present in organic forms, and recent
studies have shown that dissolved organic nitrogen (DON) compounds are
often the predominant form of N in soil solutions and leachates (e.g. Qualls
and Haines, 1991). Relatively little information, however, is available on
either the origin or processes controlling DON in soil water. One hypothe-
sis is that DON serves as an intermediate N pool between inorganic N and
'insoluble' organic N fractions of the soil during mineralization of organic
matter and immobilization of inorganic N, respectively. However, as
observed for dissolved organic carbon (DOC), the availability and mobility
of DON within the soil are likely to be controlled by sorption processes. A
major source of dissolved organic matter (DOM) to the soil is the decom-
position of plant material and the release of soluble organic compounds,
such as DON. Another source of DON is direct release from plant roots
into the rhizosphere. The detection of free amino acids in root exudates was
reported many years ago (Smith, 1969), but the dynamics of this N were
not followed mainly because of problems associated with extraction and
analysis.
The objective of this study was to determine the influence of tempera-
ture and vegetation cover on DON in a peaty podzol. Firstly, we followed
the temporal changes in extractable DON and mineral N in soil cores
incubated at 5, 10 and 15
C, to determine whether DON was depleted
when net mineralization of N occurred. Secondly, intact cores of the same
soil, with and without vegetation, were leached with artificial rain for
°
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