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| Spatial heterogeneity of soil nitrogen in six natural secondary forests in mountainous region of Northern China |
| Yang Xiuqing,Han Youzhi |
| College of Forestry,Shanxi Agricultural University,030801,Taigu,Shanxi,China |
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Abstract Understanding distribution of soil nitrogen at the natural secondary forest stands is important for studying the ecological processes of forest and forest ecosystem function.In order to study the spatial variation of soil nitrogen in natural secondary forest in mountainous region of Northern China,six sample plots(50m×50m) of different forests types were selected,and geostatistic semivariogram analysis method was used to quantified the spatial distribution of soil nitrogen in these sample plots.Results showed that: 1)the amount of total nitrogen in the secondary broad-leaved stands was higher(3100-4500mg/kg),but that in the conifer stands was relatively lower(900-1300mg/kg);all types of forest soils with a much lower NO-3-N amount were typically dominated by NH+4-N;2) the spatial heterogeneity characteristics of soil nitrogen were significantly different in forest types.Total nitrogen had large intensity of variance and weak spatial auto-correlativity(the variance caused by random factors to total variance ratio was 42.7%) in broad-leaved and coniferous mixed forest,but relatively smaller intensity and strongly auto-correlated variance(accounted for 72.2%-81.0% of total variance) in conifer stands,total nitrogen amount appeared as a patch distribution in conifer stands;3) the heterogeneity characteristics of available nitrogen forms mainly appeared as follows: NH+4-N was strongly auto-correlated but NO-3-N was of a weak variance degree in the broad-leaved stands.However,there was a relatively apparent spatial variance about NO-3-N in the conifer stands;4) there was an effect of forest types on spatial heterogeneity characteristics of total and available nitrogen;5) the difference of vegetation kinds,composition,diversity and spatial distribution patterns of tree species caused by them as shown above have been the important causes of affecting total nitrogen amount,nitrogen mineralization and further leading to variance of nitrogen forms among stands or different spatial sampling site inner every stand.
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Received: 26 September 2010
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