Nitrogen mineralization and gaseous nitrogen losses from waterlogged and drained organic soils in a black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forest
Black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forests on peat soils have been reported to be hotspots for high nitrous oxide (N<sub>2</sub>O) losses. High emissions may be attributed to alternating water tables of peatlands and to the incorporation of high amounts of easi...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-06-01
|
| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/2961/2014/bg-11-2961-2014.pdf |
| Summary: | Black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forests on peat soils
have been reported to be hotspots for high nitrous oxide (N<sub>2</sub>O) losses.
High emissions may be attributed to alternating water tables of peatlands and
to the incorporation of high amounts of easily decomposable nitrogen (N) into
the ecosystem by symbiotic dinitrogen (N<sub>2</sub>)-fixation of alder trees. Our
study addressed the question to what extent drainage enhances the emissions
of N<sub>2</sub>O from black alder forests and how N turnover processes and
physical factors influence the production of N<sub>2</sub>O and total
denitrification. The study was conducted in a drained black alder forest with
variable groundwater tables at a southern German fen peatland. Fluxes of
N<sub>2</sub>O were measured using the closed chamber method at two drained sites
(D-1 and D-2) and one undrained site (U). Inorganic N contents and net N
mineralization rates (NNM) were determined. Additionally a laboratory
incubation experiment was carried out to investigate greenhouse gas and
N<sub>2</sub> fluxes at different temperature and soil moisture conditions.
Significantly different inorganic N contents and NNM rates were observed,
which however did not result in significantly different N<sub>2</sub>O fluxes in the
field but did in the laboratory experiment. N<sub>2</sub>O fluxes measured were low
for all sites, with total annual emissions of 0.51 ± 0.07 (U),
0.97 ± 0.13 (D-1) and
0.93 ± 0.08 kg N<sub>2</sub>O–N ha<sup>−1</sup> yr<sup>−1</sup> (D-2). Only 37%
of the spatiotemporal variation in field N<sub>2</sub>O fluxes could be explained
by peat temperature and groundwater level, demonstrating the complex
interlinking of the controlling factors for N<sub>2</sub>O emissions. However,
temperature was one of the key variables of N<sub>2</sub>O fluxes in the incubation
experiment conducted. Increasing soil moisture content was found to enhance
total denitrification losses during the incubation experiment, whereas
N<sub>2</sub>O fluxes remained constant. At the undrained site, permanently high
groundwater level was found to prevent net nitrification, resulting in a
limitation of available nitrate (NO<sub>3</sub><sup>−</sup>) and negligible gaseous N
losses. N<sub>2</sub>O flux rates that were up to four times higher were measured
in the incubation experiment. They reveal the potential of high N<sub>2</sub>O
losses under changing soil physical conditions at the drained alder sites.
The high net nitrification rates observed and high NO<sub>3</sub><sup>−</sup> contents bear
the risk of considerable NO<sub>3</sub><sup>−</sup> leaching at the drained sites. |
|---|---|
| ISSN: | 1726-4170 1726-4189 |