Exchange of Atmospheric Methane with Soils of Forests and Pastures in Brazil

关于大气甲烷与热带土壤交换的为数不多的数据是模棱两可的。旱地温带土壤被认为是CH4的汇，场地干扰通常会降低土壤吸收CH4的速度，但这些概括在热带地区还没有得到广泛的检验。事实上，初步证据表明，亚马逊东部质地良好的土壤中的高呼吸速率和低气体扩散系数可以导致热带森林土壤产生甲烷。此外，关于土地利用变化对热带地区CH4通量的影响的知识充其量也是最基本的。这项研究的第一个目标是评估由土地利用、昼夜循环、季节循环、站点内异质性以及亚马逊东部原始林、次生林、不同年龄的活跃牧场和废弃牧场事件引起的CH4通量的变化。第二个目标是检验两个机械假说：土壤中气体的扩散率控制着CH4的排放；NH4+有效性的提高可以抑制CH4的消耗。根据222Rn分布和CClF3示踪剂实验估算的扩散系数预计将是影响甲烷生产和消费的主要因素。表征这一活跃伐木和牧场地区土地利用的影响，并从机械上描述这些影响，将有助于我们更好地理解人类活动如何影响大气甲烷。

The few data that exist on exchange of atmospheric methane with tropical soils are equivocal. Upland temperate soils are thought to be sinks of CH4, and site disturbance usually decreases rates of CH4 uptake by soils, but these generalizations have not been tested widely in the tropics. Indeed, preliminary evidence suggests that high rates of soil respiration and low gas diffusivities in fine textured soils of the eastern Amazon can result in CH4 production in tropical forest soils. Moreover, knowledge of the effects of changing land uses on CH4 fluxes in the tropics is rudimentary at best. The first objective of this research is to assess variation in CH4 fluxes caused by land uses, diurnal cycles, seasonal cycles, within-site heterogeneity, and events in primary forests, secondary forests, active pastures of varying age, and abandoned pastures in eastern Amazon. The second objective is to test two mechanistic hypotheses: that gas diffusivity in soils controls CH4 fluxes; and that enhanced NH4+ availability can inhibit CH4 consumption. It is expected that diffusivity, estimated from profiles of 222Rn and from CClF3 tracer experiments, will be the dominant factor affecting production and consumption of CH4. Characterizing the effects of land use in this area of active logging and ranching, and describing these effects mechanistically will improve our understanding of how human activities impact atmospheric methane.