Monday, 10 July 2006

Properties of Typical Forest Soils of China in Different Climatic Zones Affecting Methane and Ethylene Consumption and Nitrous Oxide Production.

Xingkai Xu, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Soil properties along with atmospheric temperature can contribute to the site-specific variations of methane and ethylene consumption and nitrous oxide production of forest soils. Two- to three-year in situ measures was done to monitor methane consumption and nitrous oxide emission in one typical tropical seasonal rainforest (10116'E, 2156'N), sub-tropical mixed broadleaf forest (11232'E, 2310'N) and temperate broadleaf Korean pine forest (12828'E, 4224'N) with different natural atmospheric N depositions. The results obtained show that all forest soils consume atmospheric methane and emit nitrous oxide to the atmosphere, and that their yearly site-specific variations mostly result from the differences of soil properties and yearly rainfall. The presence of extrinsic ethylene can affect the consumption of atmospheric methane by surface forest soils. In selected temperate forests, it was observed that maximal consumption of methane and ethylene occur in the 2.5-7.5cm soil layer, but their consumption is maximal in the 0-2.5cm soil layer from both tropical seasonal rainforest and sub-tropical forests. Step-wise regression and factor analysis show that the differences of methane and ethylene consumption in the soils at depths mostly result from depths of forest floors and soil properties such as soil pH, nitrogen status, microbial biomass C and N, soluble organic C, microbial metabolic quotient and heavy metal oxides. The differences of soil properties in different land uses (e.g. rainforest, secondary forest and tea garden) and due to forest succession account for the variations of methane and ethylene consumption by soils at depths. According to the ethylene formation in the soil slurry (soil/water, 1/2.5) and ethylene consumption by soils at depths, the cycling of ethylene beneath forest floors may affect the consumption of atmospheric methane by forest soils. The availability of N in the uppermost mineral forest soils is one of main parameters influencing nitrous oxide. Maximal nitrous oxide formation was observed in the 0-2.5cm soil layer from all selected forest stands across China, and was associated with soil properties. Combining both in situ measures and laboratory-based studies indicates that autotrophic and heterotrophic nitrification mainly contributes to total nitrous oxide emission from forest soils, especially to that from the 0-2.5cm soil layer. The contribution of heterotrophic nitrification to the total nitrous oxide emission was variable with forest stands and with seasons. It was of important to discuss the relation between partition of nitrous oxide formation and soil properties under tropic different land uses and during forest succession. Acknowledgements: This research was funded by the National Natural Sciences Foundation of China (agreement no. 20477044) and by the Hundred Talents Project from the Chinese Academy of Sciences. Special thanks are due to support from Prof. Yuesi Wang, Mrs. Bin Yuan and Wenpeng Yu, and Ms. Jin Wei from the Institute of Atmospheric Physics, Chinese Academy of Sciences.

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