| Forest soil,the largest carbon and nitrogen pools,plays an important role in studying the climatic change and globe warming issues.Much more studies focus on the research with soil carbon and nitrogen due to global warming.Moreover,soil organic carbon(SOC)and total nitrogen(TN),which influences soil fertility and plant growth,are the most important parts of soil nutrient.The research were collected 200 samples with topsoil(0-20 cm),228 samples with soil profile in different climatic zones including Jiagedaqi in Heilongjiang province,Qinyuan in Shanxi province,Shennongjia in Hubei province,Jinzhai in Anhui province and Dehua in Fujian province.The research were analyzed the effect of impact factors(mean annual temperature,mean annual precipitation,elevation,topography,slope position,forest type,soil layer and soil type)on SOC concent and TN concent,and analyzed the interaction between SOC concents and-TN concents with topsoil and soil profile and impact factors by the path analysis model of structural equation model;meanwhile,the research were investigated the distribution of SOC and TN in northern subtropical forest on different slope positions and forest types.Study results showed:SOC concent and TN concent order with topsoil:the upper slope<the mid slope<the lower slope,deciduous broadleaved forest>coniferous forest and mixed conifer and deciduous broadleaved forest;there was a highly significant(P<0.01)correlation between C/N ratio and slope,and C/N ratio increased in the order:the upper slope<the mid slope and the lower slope;there were a significant(P<0.05)correlation between SOC concent,TN concent,mean annual temperature,slope position,forest type,bulk density and soil type,and a significant(P<0.05)correlation between SOC content and mean annual precipitation,meanwhile it was highly significant(P<0.01)correlation between SOC,TN and C/N ratio.R2 of the path analysis model was 0.967,and the influence weight of each factor on SOC concent in topsoil decreased in the order:TN concent>mean annual precipitation>slope position>mean annual temperature>C/N ratio>soil type>forest type>bulk density.SOC concent and TN concent with soil profile decreased in the order:A layer>B layer>C layer,the mid slope and the lower slope>the upper slope;SOC and TN had a significance(P<0.05)correlation with mean annual temperature,slope,soil layer,bulk density and soil type separately;there was a significance(P<0.05)correlation between TN concent and mean annual precipitation.It was a significance(P<0.05)correlation between C/N ratio with soil profile and mean annual temperature,slope position,soil layer and bulk density.R2 of the path analysis model was 0.980,and the influence weight of each factor on SOC concent of soil profile decreased in the order:TN concent(0.878)>soil layer(-0.728)>slope position(0.333)>C/N ratio(0.274)>mean annual temperature(-0.122)>soil type(0.037);besides,the influence weight of the first three(TN concent,soil layer,slope position)were respective 37%,31%and 14%.In the studying area of Mt.Shennongjia,SOC and TN had a significance(P<0.05)correlation with forest type and slope separately,SOC and TN concent and storage order with the same forest type:the upper slop<the mid slope<the lower slope,under the same slope:mixed conifer and deciduous broadleaved forest<deciduous broadleaved forest<coniferous forest.The soil C/N ratios of deciduous broadleaved forest,mixed conifer and deciduous broadleaved forest and tussock showed that the lower slope were higher than the upper slope,and the mid slope lined between them,while the soil C/N ratio of coniferous forest decreased in the order the mid slope>the upper slop>the lower slope;in deciduous broadleaved forest,the soil C/N ratio of the lower slope(18.03)was 1.35 times of that in the upper slope(13.36)and was 1.41 times of that in the mid slope(12.72).In the upper slope and mid slope,the soil C/N ratios of coniferous forest were the highest,followed by deciduous broadleaved forest and mixed conifer and deciduous broadleaved forest,and soil C/N ratios of tussock were the lowest;in the lower slope,the soil C/N ratio decreased in the order deciduous broadleaved forest>coniferous forest = mixed conifer and deciduous broadleaved forest>tussock>larix kaempferi artificial forest.In the same forest type or slope position,the soil C/N ratio was larger in the surface layer than that in the deep layer,the soil C/N ratios in A layer and B layer were 1.07 to 2.12 and 1.02 to 1.81 times that of those in C layer.The research could see that SOC concent and TN concent had a highly correlation.There were different weights between SOC and TN with impact factors in topsoil and soil profile.It could not be ignored that effect of forest type and slope position to the distribution of SOC and TN in northern subtropical forest.Results shall provide scientific data to spatial pattern of SOC and TN in forest ecosystem in future. |
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