转变土地利用方式对桂西喀斯特地区土壤氧化CH4的影响

Effect of Land-use Changes on the Methane Oxidation in Karst Soils of West Guangxi

选取桂西喀斯特地区分布最广的石灰土和黄壤,通过野外通量观测和实验室CH4氧化动力学试验,研究弃耕或退耕还林对土壤CH4通量的影响。结果表明,对于石灰土,CH4年均通量为弃耕地LS-3[-64.30μg/,(m^2·h)]>灌草地LS-1[-48.96μg/(m^2·h)]>旱地LS-2[29.61μg/(m^2·h)];对于黄壤,退耕林地YS-2[-36.95μg/(m^2·h)]>旱地YS-1[-29.44μg/(m^2·h)]。各点土壤CH4氧化速率动力学遵循米氏方程,最大cH4氧化速率(Vmax)介于400~4347pmol/(g·h)之间,半饱和常数值介于72-878.3μL/L之间,石灰土土壤Vmax值是黄壤的两倍以上,具有更高的氧化潜力。土壤CH4通量的季节变化不明显,释放峰或吸收峰出现在秋冬季节。温度有利于促进土壤对大气CH4的吸收。土壤水分对土壤氧化CH4的抑制作用在受人为干扰少的LS-1和LS-3表现显著,而对于旱地LS-2,YS-1及林地YS-2,NH^+4-N含量成为土壤氧化CH4的主要限制因素。总之,土壤恢复有利于土壤氧化大气CH4,这不仅取决于土壤理化性质、甲烷微生物群落的变化,还受到区域气候因素的影响。

The two most widely distributed soils (lime soil and yellow soil)in the karst area of southwest Guangxi were selected as research objects in this study.The effects of the land use change,from abandonment to reforestation,on CH4oxidation were studied on the basis of field inspection and laboratory soil CH4 oxidation kinetics test.The resuhs revealed that the land use change affects the CH4 flux variously for different soils,e.g.CH4 fluxes in lime soils decreased following the order of abandoned land LS-3[-64.30μg/(m^2·h)]>natural bushes LS-1[-48.96μg/(m^2·h)]>cultivated land LS-2[29.61μg/(m^2·h)],while in yellow soils,the order was reforest YS-2[-36.95μg/(m^2·h ]>cultivated land YS-1[-29.44μg/(m^2·h)].The CH4 oxidation in soils followed the standard Michaelis-Menten kinetics,with CH4 Vmax values of 400to 4347pmo1/(g,h)and Km values of 72-878.3μL/L.The Vmax value measured in lime soils was more than twice of that in yellow soils,indicating the higher oxidation potential of lime soils.The tend- ency of seasonal CH4 flux changes was indistinct,however the release and absorption peaks were usually found in autumn or winter. Generally,the soil temperature had a positive effect on CH4 uptake.The soil moisture had a remarkable negative effect on CH4 fluxes in soils,LS-1and LS-3,which experienced slight human disturbance,while the soil ammonium nitrogen content was the dominated fac- tor for CH4 oxidation in soils,i.e.dry lands LS-2 and YS-1 and forest land YS-2.Our results suggested that the soil restoration has a positive effect on CH4 consumption,but its degree depends on not only the change of soil physical and chemical properties and methane microbial community but also regional climate factors.