华北山地6种天然次生林土壤氮素的空间异质性特征

 利用地统计学理论和方法研究华北山地次生林区6种天然次生林土壤氮素的空间异质性特征。结果表明:1)次生阔叶林土壤总氮质量分数相对较高（3 1004 500 mg/kg）,而针叶林相对较低（9001 300 mg/kg）,各森林类型土壤中有效NH4+-N质量分数均高于有效NO3--N,形成以NH4+-N占优势的氮营养生境;2)针阔混交林中,土壤全氮的变异强度最大,变异的空间相关性较差（随机性变异占总变异的42.7%）,针叶林中,全氮空间变异强度相对较弱,但以自相关变异为主（结构方差比为72.2%81.0%）,呈现弱的斑块分布特征;3)阔叶林中,NH4+-N具有很强的空间自相关变异,NO3--N异质性程度相对较弱,针叶林中,NH4+-N变异强度较小,而NO3--N空间变异却相对明显;4)不同森林类型对土壤全氮及各有效氮形态的空间异质性特征有影响;5)植被种类、植被组成、植被多样性等因素的差异及由此导致的树种空间分布格局是影响总氮量及氮矿化,进而导致氮素不同形态在林分间甚至林分内不同空间样点间异质性形成的重要原因。

Spatial heterogeneity of soil nitrogen in six natural secondary forests in mountainous region of Northern China

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.