Abstract
Strong
seasonal variability of hygric and thermal soil conditions are a
defining environmental feature in northern Australia. However, how such
changes affect the soil–atmosphere exchange of nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2)
is still not well explored. By incubating intact soil cores from four
sites (three savanna, one pasture) under controlled soil temperatures
(ST) and soil moisture (SM) we investigated the release of the trace gas
fluxes of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to denitrification was measured using the helium gas flow soil core technique. Under dry pre-incubation conditions NO and N2O emissions were very low (<7.0 ± 5.0 μg NO-N m−2 h−1; <0.0 ± 1.4 μg N2O-N m−2 h−1) or in the case of N2O, even a net soil uptake was observed. Substantial NO (max: 306.5 μg N m−2 h−1) and relatively small N2O pulse emissions (max: 5.8 ± 5.0 μg N m−2 h−1)
were recorded following soil wetting, but these pulses were short
lived, lasting only up to 3 days. The total atmospheric loss of nitrogen
was generally dominated by N2 emissions (82.4–99.3% of total
N lost), although NO emissions contributed almost 43.2% to the total
atmospheric nitrogen loss at 50% SM and 30 °C ST incubation settings
(the contribution of N2 at these soil conditions was only 53.2%). N2O
emissions were systematically higher for 3 of 12 sample locations,
which indicates substantial spatial variability at site level, but on
average soils acted as weak N2O sources or even sinks. By
using a conservative upscale approach we estimate total annual emissions
from savanna soils to average 0.12 kg N ha−1 yr−1 (N2O), 0.68 kg N ha−1 yr−1 (NO) and 6.65 kg N ha−1 yr−1 (N2). The analysis of long-term SM and ST records makes it clear that extreme soil saturation that can lead to high N2O and N2
emissions only occurs a few days per year and thus has little impact on
the annual total. The potential contribution of nitrogen released due
to pulse events compared to the total annual emissions was found to be
of importance for NO emissions (contribution to total: 5–22%), but not
for N2O emissions. Our results indicate that the total
gaseous release of nitrogen from these soils is low and clearly
dominated by loss in the form of inert nitrogen. Effects of seasonally
varying soil temperature and moisture were detected, but were found to
be low due to the small amounts of available nitrogen in the soils
(total nitrogen <0.1%).
Original language | English |
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Pages (from-to) | 6047-6065 |
Number of pages | 19 |
Journal | Biogeosciences |
Volume | 11 |
Issue number | 21 |
DOIs | |
Publication status | Published - 2014 |