| Methane is an important greenhouse gas and has a relative global warming potential 25 times that of CO2 over a 100-year time level, and is estimated to contribute 20% to the radioactive force driving global climate change. The atmospheric concentration of CH4 has increased by 150% since the industrial revolution, and achieved to 1774 ppb in 2005. Human disturbances, especially land-use change have great influence on methane cycle in terrestrial ecosystems. A large biological sink is the oxidation of CH4 by microorganisms in aerobic soils, and strength of this sink is similar to annual amount of CH4 increase (30Tg·a-1), so alterations of this sink is important for the change of atmospheric CH4 concentrations. However, little is known about the upland soil CH4 sink, which is unfavorable to formulate greenhouse gas emissions list.We selected an land use sequence of natural evergreen broad-leaved forest, secondary evergreen broad-leaved forest, Chinese fir plantations and orchard with similar site conditions in jianou, Fujian. The effect of land-use change on soil CH4 oxidation was studied with the method of'space-for-time'substitution. The result will provide basic data to formulate greenhouse emissions list and technical supports to develop technology of carbon sink in the mountainous area, and provide the scientific basis for adjustment to land-use and recovery measures of soil CH4 sink.Base on one year in situ observation, some results were as follows:the seasonal variation of soil CH4 oxidation rate was consistent with temperature change. The average CH4 oxidation rate of upland soil ranged from 22.65 to 29.25μg·m-2·h-1, which was higher than that in tropical forests and lower than in temperate forests. The CH4 oxidation rates of natural evergreen broad-leaved forest, secondary forest, plantations and orchards were 257.67,207.04,242.90 and 161.89 mg·m-2·a-1, respectively. The rate of CH4 oxidation decreased by 2-40% resulting from land-use change, with the largest declines in the orchard. Following the conversion of natural evergreen broad-leaved forest to secondary (plantation) forest and the farming land, the CH4 oxidation rate reduced by 7.13%-40%, which were lower than average value in global level. The capacity of CH4 oxidation was different in land use types. The rate of CH4 oxidation was significant positively correlated to soil temperature. The temperature sensitivity of CH4 oxidation was decreased from 2.24 in the natural evergreen broad-leaved forest to 1.11 in the orchard, and the average decreased by 8.92%. Compared with the natural evergreen broad-leaved forest, the CH4 oxidation rates of secondary forest, plantation and orchard were decrease by 15.18%,1.69% and 22.57%, respectively. On certain temperature and humidity conditions, all kinds of the soils had the capacity of CH4 oxidation, with the rate from 0.02μg·g-1·d-1 to 0.15μg·g-1·d-1.The highest soil CH4 oxidation rates in evergreen broad-leaved forest, secondary forest and plantations were found at 5-10 cm depth, whereas oxidation rate at 0-5cm horizon was highest in the orchard. The CH4 oxidation rate was positively correlated to soil organic matter and nitrogen contents, negatively to soil bulk density. There was no clear relationship between CH4 oxidation rate and soil water content. |
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