林分类型和氮添加对亚热带森林土壤氧化亚氮排放的影响OACSCDCSTPCD

To reveal the response of soil N2O emissions to forest types and nitrogen addition in subtropical forests,soil samples were collected from Castanopsis carlesii secondary forests,Cunninghamia lanceolata plantation and Pinus massoniana plantation located in Sanming City,Fujian Province.A microcosm was carried out and the soils were amended with NH4 NO3 at four levels:no nitrogen addition(N0 mg/kg),low nitrogen addition(N10 mg/kg),medium nitrogen addition(N25 mg/kg)and high nitrogen addition(N50 mg/kg)to determine N2O flux.The results showed that nitrogen addition generally decreased soil p H,while increased soil NH4+-N and NO3--N contents.The cumulative N2O emissions in C.lanceolata and P.Massoniana plantations with no nitrogen addition were 9.67 and 9.62 mg/kg,respectively,and were significantly higher than 6.81mg/kg in C.carlesii secondary forest.Similar trend was found in soils with low nitrogen addition.However,in the medium and high nitrogen addition treatments,there were no significant differences in cumulative N2O emissions among the three forest stand types.Nitrogen addition increased soil N2O emission in all the three forest types,with the effect size of low nitrogen addition on N2O emissions in secondary forest soil being 0.01,significantly lower than the effect size of 0.45 in C.lanceolata and P.massoniana plantation soils.Conversely,the effect sizes of medium and high nitrogen additions on N2O emission were significantly higher in secondary forests than plantations.These results indicated that N2O emissions in secondary forests was more likely to be stimulated by medium or high nitrogen addition.Cumulative N2O emissions were positively associated with soil NH4+-N and NO3--N contents(p<0.01),rather than soil p H,indicating that available nitrogen was the main factor controlling soil N2O emissions in forest soils under nitrogen additions.Taken together,N2O emissions were higher in plantation soils than in secondary forest soil,but N2O emissions in secondary forests soil were more sensitive to medium and high nitrogen additions.