土地利用和环境因子对表层土壤有机碳影响的尺度效应分析：以陕北黄土丘陵沟壑区为例

Abstract

土壤表层有机碳对土地利用和环境因子的变化非常敏感，并具有尺度变异特征。研究不同尺度上表层土壤有机碳的空间分布及其与土地利用与环境因子的关系对于评价黄土丘陵沟壑区表层土壤有机碳状况具有重要意义。选择黄土丘陵沟壑区安塞集水区和集水区内典型小流域——沐浴小流域作为研究区，探讨两个尺度上，表层土壤有机碳的分布特征及其与土地利用、环境因子的关系。结果表明：（1）土地利用方式对有机碳的影响在不同尺度上差异明显，对于不同利用方式下的有机碳含量，沐浴小流域从高到低依次是荒草地 >林地 >灌木林地 >耕地，安塞集水区则依次为林地 >灌木林地 >耕地 >荒草地；（2）对于不同利用方式下的土壤有机碳密度，沐浴小流域从高到低依次是荒草地 >林地 >耕地 >灌木林地，安塞集水区则是林地>耕地>荒草地>灌木林地；（3）在沐浴小流域和安塞集水区两个尺度上，坡向、坡度和植被盖度均与有机碳含量和有机碳密度正相关，而相对海拔、土地利用与有机碳密度负相关；（4）在小流域尺度上，海拔高度、坡位、土地利用与有机碳含量负相关，坡位与有机碳密度负相关，但是在集水区尺度上，相关性则与此相反。;Land use and environmental factors are considered significant in regulating the spatial distribution of surface soil organic carbon (SOC), but are not equally important at different scales. Accurate knowledge of SOC stocks and the effects of environmental factors on SOC are crucial, both from the perspective of regional carbon budgets and appropriate landscape management of SOC. The Muyu small watershed and the Ansai catchment in loess hilly-gully area were taken as study area in the paper. On the basis of soil sampling in the field, 35 and 79 samples were taken separately in Muyu small watershed and Ansai catchment. Classical statistics and RDA were applied to study on the relationship of the distribution of SOC, soil organic carbon density (SOCD) with land use and environmental factors at two different scales. The research results were as follows. The effects of land use type on SOC and SOCD had significant difference at two scales. SOC varied with land use in the order: grass land > woodland > shrubland > farmland at the Muyu small watershed. And the order was woodland > shrubland > farmland > grassland at the Ansai catchment. Meanwhile, the SOCD was highest in the grassland and declined as follows: grassland > woodland > farmland > shrubland at the Muyu small watershed, and it was highest in the woodland and declined as: woodland > farmland > grassland > shrubland at the Ansai catchment. SOC and SOCD showed scale effects under different influence of land use. The main land use at the Muyu watershed was grassland. The soil physical and chemical properties were good enough to protect the soil and water. Thus the SOC and SOCD were both higher than other land use, which was different from that at the Ansai catchment. There were a lot of woodland and shrubland at the Ansai catchment. Since woodland was the optimal land use type to keep soil and water, and the SOC and SOCD were much higher in woodland at the catchment. Also since changes in land use had influences on physical, chemical and biological soil attributes, they changed SOC and SOCD by disturbing the equilibrium between the formation and mineralization of soil organic matter. The land use change played different roles in affecting SOC and SOCD at different scales.<br>Then we chose slope, slope position, slope aspect, altitude, vegetational cover and land use as environmental factors. Among them, aspect, slope and vegetational cover were positively related to the SOC and SOCD at both the Muyu watershed and the Ansai catchment. Altitude, slope position and land use were negatively related to SOC at the Muyu watershed while they were positively related to SOC at the Ansai catchment. Altitude and land use were negatively related to SOCD at two scales. Slope position was negatively related to SOCD at the Muyu watershed, and positively at the Ansai catchment. The influences of environmental factors were varies: slope aspect, slope and slope position decided the migration direction and speed of material, altitude affected the vertical distribution of the hydrothermal conditions, and vegetational coverage, with land use, reflected the input and output of soil organic carbon. But since different geographical conditions, the influences of those environmental factors were complex.