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Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia

Livesley, Stephen, Grover, Samantha. P., Hutley, Lindsay B., Jamali, Hizbullah, Butterbach-Bahl, Klaus, Fest, Benedict, Beringer, Jason and Arndt, Stefan (2011). Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia. Agricultural and Forest Meteorology,151:1440-1452.

Document type: Journal Article

IRMA ID 82057923xPUB54
Title Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia
Author Livesley, Stephen
Grover, Samantha. P.
Hutley, Lindsay B.
Jamali, Hizbullah
Butterbach-Bahl, Klaus
Fest, Benedict
Beringer, Jason
Arndt, Stefan
Journal Name Agricultural and Forest Meteorology
Publication Date 2011
Volume Number 151
ISSN 0168-1923   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-80052280937
Start Page 1440
End Page 1452
Total Pages 12
Place of Publication Netherlands
Publisher Elsevier BV
HERDC Category C1 - Journal Article (DIISR)
Abstract Tropical savanna ecosystems are a major contributor to global CO 2, CH 4 and N 2O greenhouse gas exchange. Savanna fire events represent large, discrete C emissions but the importance of ongoing soil-atmosphere gas exchange is less well understood. Seasonal rainfall and fire events are likely to impact upon savanna soil microbial processes involved in N 2O and CH 4 exchange. We measured soil CO 2, CH 4 and N 2O fluxes in savanna woodland (Eucalyptus tetrodonta/Eucalyptus miniata trees above sorghum grass) at Howard Springs, Australia over a 16 month period from October 2007 to January 2009 using manual chambers and a field-based gas chromatograph connected to automated chambers. The effect of fire on soil gas exchange was investigated through two controlled burns and protected unburnt areas. Fire is a frequent natural and management action in these savanna (every 1-2 years). There was no seasonal change and no fire effect upon soil N 2O exchange. Soil N 2O fluxes were very low, generally between -1.0 and 1.0μg Nm -2h -1, and often below the minimum detection limit. There was an increase in soil NH 4 + in the months after the 2008 fire event, but no change in soil NO 3 -. There was considerable nitrification in the early wet season but minimal nitrification at all other times. Savanna soil was generally a net CH 4 sink that equated to between -2.0 and -1.6kg CH 4ha -1y -1 with no clear seasonal pattern in response to changing soil moisture conditions. Irrigation in the dry season significantly reduced soil gas diffusion and as a consequence soil CH 4 uptake. There were short periods of soil CH 4 emission, up to 20μg Cm -2h -1, likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO 2 fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH 4 fluxes, but a much stronger relationship with soil CO 2 fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N 2O source, and possibly even a sink. Annual soil CH 4 flux measurements suggest that the 1.9million km 2 of Australian savanna soils may provide a C sink of between -7.7 and -9.4 Tg CO 2-e per year. This sink estimate would offset potentially 10% of Australian transport related CO 2-e emissions. This CH 4 sink estimate does not include concurrent CH 4 emissions from termite mounds or ephemeral wetlands in Australian savannas.
Keywords Carbon dioxide
Nitrous oxide
Savanna woodland
Soil gas diffusion
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