Soil Methane Uptake Rates And Factors In Various Regeneration Of Forests In Mid-subtropical China

Forest soil is an important CH4 sink or source through the activity of methanotrophic arid methanogenes bacteria.The change of land use could affect the rates of soil uptake CH4 seriously.In this research,we investigated in situ soil CH4 uptake rates in various types of forest regeneration,including a natural forest,a natural regeneration forest,an artificial regeneration forest,a Castanopsis carlesii artificial forest,a masson pine forest and a cunninghamia lanceolata forest in mid-subtropical China,by using a static chamber and gas chromatography technique.Additionally,we studied soil net N mineralization and nitrification rates in 0?10 cm and 10?20 cm layers for forests.We also attempted to study the community structure of methanotrophs.Our ruselts were shown as follows.All the soils of the forest stands were a sink of atmosphere CH4,with the averaged CH4 uptake rates of-60.46 ?g·m-2·h-1,-38.39 ?g·m-2·h-1,-35.65 ?g·m-2·h-1,-37.34?g·m-2·h-1,-40.60 ?g·m-2·h-1,-38.90 for the natural forest?the natural regeneration forest,the artificial regeneration forest,the Castanopsis carlesii artificial forest,the masson pine forest and the cunninghamia lanceolata forest,respectively.And the CH4 uptake rates of the natural forest were significantly greater than in other forests(P<0.05).But there was no significant difference between other five forests(P>0.05).Soil CH4 uptake rates of the forests were significantly correlated to soil moisture(P<0.05),but not to soil temperature(P>0.05).The N net nitrification rates in 0-10 cm for the six forests were 0.917 mg·kg-1·d-1,0.197 mg-kg-1·d-1,0.060 mg·kg-1·d-1,0.729 mg-kg-1·d-1,0.601 mg·kg-1·d-1,0.049 mg·kg-1·d-1,respectively;and the N net nitrification rates in 10?20 cm for the six forests were 0.249 mg·kg-1·d-1,0.053 mg·kg-1·d-1,0.015mg·kg-1·d-1,0.378 mg·kg-1.d-1,0.105 mg·kg-1·d-1,0.006 mg·kg-1·d-1,respectively.The CH4 fluxes of the six forests both in 0?10 cm,10?20 cm,were significantly correlated with the NO3-contents(P<0.05).We determined the activity of the soil methanotrophs under the six forests at three levels of initial CH4 concentration(20,200 and 2000 ppm)thus distinguishing the activities of low-and high-affinity methanotrophs.we found that the CH4 uptake rate of artificial regeneration forest in 0?10 cm was the lowest under 20 ppm,and significantly lower than the nature forest(P<0.05),but the CH4 uptake ratesof it was the highest in 2000 ppm,and significantly higher than the nature forest(P<0.05);and there were no significant differences in CH4 uptake rates in 10?20 cm between the six forests under 20 and 200 ppm,but the CH4 uptake rates of artificial regeneration forest was the highest in 2000 ppm.