亚热带丘陵小流域土壤碳氮磷生态计量特征的空间分异性

SPATIAL VARIATION OF ECOLOGICAL STOICHIOMETRY OF SOIL C,N AND P IN A SMALL HILLY WATERSHED IN SUBTROPICS OF CHINA

了解土壤碳氮磷生态化学计量特征的空间变异有助于土壤养分管理。以湖南省长沙县金井镇脱甲河小流域（52km2）为研究区，系统分析了亚热带丘陵小流域表层（0～20em）土壤碳氮磷的生态化学计量特征及其空间变异性。该流域土壤有机碳（SOC）、全氮（TN）和全磷（TP）平均含量分别为13．09、1．50和0．51gkg-1，C：N、C：P和N：P平均值分别为10．42、72．71和7．19，均具有高等变异水平和中等程度的空间自相关性。土壤C：N、C：P、N：P高值区域主要分布在海拔高、人为干扰少和肥料使用少的林地区，而低值区主要分布在海拔较低、人类活动频繁以及化肥施用量大的农田区。菜地、茶园、林地和稻田等不同土地利用方式下，土壤C：N：P差异显著；在高海拔和陡坡地区，土壤C：N：P均明显偏高。这表明研究区域表层土壤碳氮磷比率的空间分异与土地管理措施和地形有着密切的关系。

The study on ecological stoichiometric characteristics of elements in soils is important to revealing mechanisms of the circulation and balance of soil carbon, nitrogen, phosphorus and other elements, and the knowledge of spatial variance of the ecological stoichiometric characteristcs of soil carbon, nitrogen and phosphorus is conducive to soil nutrient management. Spatial distributions of soil organic carbon （ SOC ） , total nitrogen （ TN ） , total phosphorus （ TP ） and stoichiometric characteristcs of soil C, N and P in the topsoil （ 0 - 20 cm ） were systematically analyzed of a representative small hilly watershed in the subtropical region of China. The watershed studied is the Tuojiahe watershed located in Jinjing Town, Changsha County, Hunan Province. A total of 529 valid soil samples of the watershed were collected by type of land use and of landform, including 21 from vegetable fields, 64 from tea gardens, 262 from rice fields and 182 from woodlands, and averaging about 10 points km-2 in density. The samples were analyzed in lab for total nitrogen, total phosphorus and organic carbon and further for ecological stoichiometric characteristcs and spatial variability of the three indices in the topsoil layer of the watershed with the aid of the GS＋Version9 and ArcGIS9.3 softwares. Results show that the mean content of soil organic carbon, total nitrogen and total phosphorus was 13.09 g kg-1, 1.50 g kg-1 and 0.51 g kg-1, with coefficients of variation being 42.4%, 38.5% and 40.8%, and variation range being 2 430m, 5 670m and 570m; respectively; and the mean ratio of C ： N, C ： P and N ： P was 10.42, 72.71 and 7.19, respectively, with coefficients of variation being 35.6%, 46.0% and 37.0%, and variation range being 3, 720m, 398m and 450m, respectively. To sum up, the soil C, N and P and their stoichiometrie ratios in the watershed are very high in spatial variation and moderate in spatial autocorrelation （C0/ （CO ＋ C） 〈~50%） . The soils high in soil C ： N, C ： P and N ： P ratio were mainly distributed in areas of woodlands high in altitude, less in human interference and low in fertilization rate, while the soils low in the ratio were mainly in the areas of farmlands, low in elevation, frequent in human activity and high in fertilization rate, which poses a marked contrast to the spatial distribution characteristics of total phosphorus. Soil C ： N ： P ratio varies sharply with the type of land use （vegetable field, paddy field, tea garden and woodlot） . In terms of soil C ： N ratio, the four types follow an order of vegetable field 〉 woodland, tea garden 〉 paddy field, in terms of C ： P ratio an order of woodland （91.37） 〉 paddy field （66.41） 〉 tea garden （53.74） 〉 vegetable field （48.79） , and in terms of N： P ratio, an order of woodland （8.79） 〉 paddy field （6.83） 〉 tea garden （5.25） 〉 vegetable field （4.10） . In addition, relationships of the ecological stoichiometric C ： N ： P ratios of the surface soils with topographic factors were analyzed. Results show that they vary with elevation, Soil C ： N ratio is 10.32, 9.84 and 12.54, C ： P ratio 66.69, 74.21 and 107.43, and N ： P ratio 6.80, 7.61 and 8.57 in soils 〈 100m, 100m - 150m and 〉 100m in elevation, respectively. Soil C ： N is significantly higher in areas high in elevation than in areas low in elevation, and similar trends are found of soil C ： P and N ： P. In the areas high in elevation and steep in slope, soil C ： N ： P ratios tend to be significantly high, which indicates that the spatial variation of soil C ： N ： P in the topsoil layer of the study area is closely related to environmental factors, such as land management practices and topography. The findings of the sudy may provide some important information and data basis for scientific management of soil nutrients in small hilly watersheds in the subtropics of China.