| Forest soils were collected from transects of different latitudes from north to south in China, followed by sealed, waterlogged and anaerobic culture with acetylene inhibition method after addition of KNO3 in a constant temperature of 25℃. Denitrification potential and production of gaseous products N2O, NO and N2 of forest soil were measured then, thus regional regulation on denitrification potential and gaseous products'composition of forest soil and its impact mechanism were discussed.The results showed that the samples had a pH range of 4.64-7.06. With the exception of forest soil from Shandong Boshan which had a pH of 7.06, all the other samples were acidic. The samples'organic carbon content varied from 23.40 to 115.53 g kg-1, the highest organic carbon content (115.53 g kg-1) appeared in forest soil sample from Mohe in Heilongjiang Province and the lowest (23.40 g kg-1) in Hainan Province. The total nitrogen content of samples were between 1.68 and 6.56 g kg-1 with the maxium in Mohe Heilongjiang and the minimum in Taishan Shandong.Soil denitrification differed greatly from each other in forest soil, and regional regularity was not obviously, neither the weaker denitrification in tropical and subtropical forest soil. Correlation analysis suggested soil denitrification potential had a obviously negative relationship with soil ratio of C/N, and negative with initial Eh (p<0.05). After carrying on stepwise regression analysis of forest soil denitrification and physical and chemical properties, a good correlation between soil denitrification and initial soil Eh,ΔNH4+-N, content of NO3-N was discovered. The regression equation was:denitrification=-0.004×initial Eh+0.006×ANH4+-N+2.385 (N=30, p=0.01,R2=0.56).In all the tested forest samples, ratio of N2O emission to total gaseous products varied a lot, between 39.7% and 98.7%. The proportion of N2O changed with latitude like a parabola, that meant it was highest in mid-latitude and from the mid to higher and lower it both descended. Correlation analysis indicated that N2O proportion has a markedly negative relationship with both soil pH(p<0.05)and SOC/OXC(p<0.05). Stepwise regression analysis demonstrated N2O ratio to the total gaseous products was well related with soil pH, SOC and soil denitrification. The regression equation was: N2Oratio=-13.725×pH-2.99×SOC+160.067 (N=30, p=0.004, R2=0.56).NO was a small fraction in denitrification products'composition, and distributed like logarithm with latitude, as the latitudes got lower and the proportions got higher. The proportions of NO in denitrification products in tropical and subtropical forest were distinctly higher than those of temperate. Correlation analysis implied the proportion was negatively related with soil SOC(p<0.01), but well positively related with soil OXC, TN and SOC/OXC(p<0.01), Stepwise regression analysis revealed N2O ratio to the total gaseous products was well related with soil SOC (p=0.004, R2=0.257), thus SOC is one of the important factors affecting NO proportion.In this study, the emission rate of NO+N2O varied a little, suggesting the rate tended to a constant. Correlation analysis showed the emission rate of denitrification product NO+N2O had a obviously negative ralationship with soil pH (p<0.01), implying the less emission of nitrogen oxide gases inhibition in soils of high pH. A relatively high emission of green house gases NO+N2O generated through the process of denitrification in tropical and subtropical zones, and denitrification could not effectively transfer reactive N to inert N (N2). The ecological and environmental significance of soil denitrification in such forest ecosystems should be re-assessed.
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