三峡库区林地土壤有机碳含量特征及效应

对三峡库区典型林分林地土壤有机碳（SOC）含量特征及对土壤物理性质、土壤结构和土壤养分效应进行研究，以期为三峡库区生态环境建设提供依据。结果表明：SOC含量表现为表层（A层）土壤（12.06～45.18 g/kg）明显大于下层土壤，大一个数量级。从土壤表层到底层，SOC含量呈明显下降趋势。由相同立地条件的灌木林改造而来的农地土壤（改造年限8 a）各层土壤SOC含量都有所降低，土壤表层SOC含量降低了10%，土壤平均有机碳含量降到为灌木林地的66%。三峡库区SOC含量与土壤物理性质直接相关，SOC含量与土壤容重和土壤毛管孔隙度存在最为明显的线性关系〖WTBX〗（R2=0.83，0.83，n=19，p<0.01）。土壤有机碳直接参与了土团聚体的形成，SOC含量与土壤团聚度和土壤团聚状况均有较好的相关关系（R2=0.62,0.76，n=19，p<0.01）。各林地土壤中氮元素含量最高，速效氮含量约为速效磷的6倍，为速效钾的2.5倍。SOC与土壤主要营养元素（N，P，K）关系中，对N元素作用最明显，特别是速效氮〖WTBX〗（R2=0.66,n=19，p<0.01），对磷的矿化起主要作用，与钾元素关系不明显。土壤有机碳是决定N和P矿化的主导因子，从土壤表层到底层C/N比值呈下降趋势，C/P值约为C/N值的6倍。阳离子交换量（CEC）与土壤团聚度之间有明显的相关关系〖WTBX〗(R2=0.49,n=19，p<0.01〖WTBZ〗)。SOC对CEC的作用主要通过改变土壤结构而实现。

CONTENT OF SOIL ORGANIC CARBON IN FOREST SOIL AND ITSEFFECTS IN THE THREE GORGES RESERVOIR AREA

In the Three Gorges Reservoir areas,the typical forest types were selected to study the soil organic carbon (SOC) and its effects on soil physical properties, soil structure,and soil nutrients,which will benefit the eco environment protection.The forest soil samples were collected according to soil genetic horizons.The content of SOC in A horizon(12.06～45.18 g/kg) was obviously larger than that in the lower horizons,over one quantitative grade.The content of SOC from top soil layer to bottom layer descended quickly.The arable land was reconstructed from shrub forest.Though the arable land has the same site with shrub forest,the content of SOC was less than that in shrub forest land after eight years cropping management.The content of SOC in A horizon in arable land decreased 10% compared to shrub forest soil,and the average content of SOC only accounted for 66% of shrub forest soil.The content of SOC had the direct effects on soil physical properties. There were obvious positive linear correlation between content of SOC and soil density and soil capillary porosity〖WTBX〗(R2=0.83,0.83,n=19，p<0.01)〖WTBZ〗.SOC also promote the soil aggregation.The content of SOC positively related to soil aggregation degree and aggregation 〖WTBX〗(R2=0.62,0.76，n=19，p<0.01)〖WTBZ〗.The content of N element was the highest in forest soil in the study area.The content of effective N was six times as large as content of effective P,and 2.5 times of effective K.In soil nutrient elements of N,P,K,the content of SOC had significant relationship with content of N,especially with effective N〖WTBX〗(R2=0.66,n=19，p<0.01)〖WTBZ〗,but not obvious with contents of P and K.The SOC played the dominant role in the N and P mineralization.From top layer to bottom layer,the C/N also descended.The C/P was about six times as great as C/N.Cation exchange capacity (CEC) was closely related to soil aggregation degree(〖WTBX〗R2=0.49,n=19，p<0.01〖WTBZ〗),which means the effect of SOC on CED was practiced by improving soil structure.