Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia
Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia
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DOI：
10.1016/j.agrformet.2011.02.001
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发表时间：
2011-11
影响因子：
6.2
通讯作者：
S. Livesley;S. Grover;L. Hutley;H. Jamali;K. Butterbach‐Bahl;B. Fest;J. Beringer;S. Arndt
中科院分区：
文献类型：
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作者：
S. Livesley;S. Grover;L. Hutley;H. Jamali;K. Butterbach‐Bahl;B. Fest;J. Beringer;S. Arndt
热带稀树草原生态系统是全球CO2、ch4和N2O温室气体交换的主要贡献者。稀树草原火灾事件代表了大量离散的碳排放，但人们对持续的土壤-大气气体交换的重要性知之甚少。季节性降雨和火灾事件可能影响稀树草原土壤微生物过程参与N2O和ch4交换。在2007年10月至2009年1月的16个月期间，我们测量了澳大利亚Howard Springs热带草原林地（高梁草上的河鼠桉树/小桉树）土壤CO2、ch4和N2O的通量，使用手动室和连接到自动化室的现场气相色谱仪。通过两个控制燃烧区和保护未燃烧区研究了火灾对土壤气体交换的影响。在这些稀树草原上，火灾是一种频繁的自然和管理行为（每1-2年）。土壤N2O交换不受季节变化和火的影响。土壤N2O通量很低，一般在- 1.0 ~ 1.0μg Nm - 2h - 1之间，往往低于最低检测限。2008年火灾发生后，土壤NH4+有所增加，NO3−没有变化。在雨季早期有相当大的硝化作用，但在所有其他时间硝化作用最小。稀树草原土壤总体上是ch4的净汇，相当于- 2.0 ~ - 1.6kg CH4ha - 1y - 1，对土壤水分条件变化的响应没有明显的季节规律。旱季灌溉显著减少了土壤气体扩散，从而减少了土壤ch4的吸收。土壤ch4排放时间短，可达20μg Cm−2h−1，可能是由自动化室内或下方的白蚁活动引起的。土壤co2通量表现出强烈的双峰型季节性模式，从旱季到雨季增加了5倍。土壤湿度与土壤ch4通量的关系较弱，但与土壤co2通量的关系要强得多，这可以解释未燃烧处理中高达70%的变化。澳大利亚热带稀树草原土壤是一个小的N2O来源，甚至可能是一个汇。年土壤ch4通量测量表明，澳大利亚190万km2的热带草原土壤每年可提供−7.7 ~−9.4 Tg CO2-e的碳汇。这一碳汇估计将抵消澳大利亚与交通相关的10%的二氧化碳排放。这一ch4汇估算不包括澳大利亚热带稀树草原白蚁丘或短暂湿地同时排放的ch4。
Tropical savanna ecosystems are a major contributor to global CO2, CH4and N2O 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 N2O and CH4exchange. We measured soil CO2, CH4and N2O 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 N2O exchange. Soil N2O 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 NH4+in the months after the 2008 fire event, but no change in soil NO3−. There was considerable nitrification in the early wet season but minimal nitrification at all other times. Savanna soil was generally a net CH4sink that equated to between −2.0 and −1.6kg CH4ha−1y−1with 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 CH4uptake. There were short periods of soil CH4emission, up to 20μg Cm−2h−1, likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO2fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH4fluxes, but a much stronger relationship with soil CO2fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N2O source, and possibly even a sink. Annual soil CH4flux measurements suggest that the 1.9million km2of Australian savanna soils may provide a C sink of between −7.7 and −9.4 Tg CO2-e per year. This sink estimate would offset potentially 10% of Australian transport related CO2-e emissions. This CH4sink estimate does not include concurrent CH4emissions from termite mounds or ephemeral wetlands in Australian savannas.