Land use change and the impact on greenhouse gas exchange in north Australian savanna soils
Land use change and the impact on greenhouse gas exchange in north Australian savanna soils
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DOI：
10.5194/bg-9-423-2012
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发表时间：
2012-01-01
期刊：
影响因子：
4.9
通讯作者：
Arndt, S. K.
中科院分区：
文献类型：
--
作者：
Grover, S. P. P.;Livesley, S. J.;Arndt, S. K.
随着人类对粮食和森林产品需求的增加，草原生态系统受到土地使用变化加速的影响。土地利用的变化已被证明既增加和减少热带稀树草原的温室气体通量和相当大的不确定性存在的非CO2通量从土壤。我们测量了甲烷（CH 4），一氧化二氮（N2 O）和二氧化碳（CO2）在一个完整的干湿季节性循环在三个重复的网站的每三个土地利用：稀树草原，年轻的牧场和老牧场（从稀树草原5-7和25-30年前，分别转换）在北方澳大利亚的道格拉斯戴利地区。通过两个灌溉试验研究了旱季结束时雨季中断的影响，从草原到牧场的土地利用变化增加了土壤的净温室气体通量。与稀树草原相比，牧场是CH 4的较弱汇，并且在潮湿条件下，旧牧场从汇变成了CH 4的重要来源。一氧化二氮的排放量一般很低，在0至5 μ g N2 O-N m（-2）h（-1）的范围内，在干燥条件下，土壤吸收N2 O是明显的。季节性降雨的中断产生了一个小的、短暂的N2 O脉冲，最高可达20 μ g N2 O-N m（-2）h（-1），在牧场土壤中最为明显。清除后土壤CO2年累积通量增加，稀树草原（14.6 tCO（2）-C ha（-1）yr（-1））的通量最低，而老牧场（18.5 tCO（2）-C ha（-1）yr（-1））和年轻牧场（20.0 tCO（2）-C ha（-1）yr（-1））。清除稀树草原使土壤温室气体排放量从53增加到约70 tCO（2）当量，增加了30%，主要是土壤CO2排放量增加和土壤CH 4汇向源的转移。季节变化明显是由土壤水分含量驱动的，支持了一种新的观点，即在热带生态系统中，土壤水分含量是土壤气体通量比土壤温度更重要的驱动因素，季节之间的温度变化不大。
Savanna ecosystems are subjected to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) over a complete wet-dry seasonal cycle at three replicate sites of each of three land uses: savanna, young pasture and old pasture (converted from savanna 5-7 and 25-30 yr ago, respectively) in the Douglas Daly region of Northern Australia. The effect of break of season rains at the end of the dry season was investigated with two irrigation experiments.Land use change from savanna to pasture increased net greenhouse gas fluxes from the soil. Pasture sites were a weaker sink for CH4 than savanna sites and, under wet conditions, old pastures turned from being sinks to a significant source of CH4. Nitrous oxide emissions were generally very low, in the range of 0 to 5 mu g N2O-N m(-2) h(-1), and under dry conditions soil uptake of N2O was apparent. Break of season rains produced a small, short lived pulse of N2O up to 20 mu g N2O-N m(-2) h(-1), most evident in pasture soil. Annual cumulative soil CO2 fluxes increased after clearing, with savanna (14.6 tCO(2)-C ha(-1) yr(-1)) having the lowest fluxes compared to old pasture (18.5 tCO(2)-C ha(-1) yr(-1)) and young pasture (20.0 tCO(2)-C ha(-1) yr(-1)). Clearing savanna increased soil-based greenhouse gas emissions from 53 to similar to 70 tCO(2)-equivalents, a 30% increase dominated by an increase in soil CO2 emissions and shift from soil CH4 sink to source. Seasonal variation was clearly driven by soil water content, supporting the emerging view that soil water content is a more important driver of soil gas fluxes than soil temperature in tropical ecosystems where temperature varies little among seasons.